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Old 02-27-2012, 02:15 PM
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Cam to bearing tolerance issues.

I have a 1971 Pontiac 400 which I have replaced the cam and bearings in twice now. The first time for more power and the 2nd because a lifter mushroomed and took a lobe with it. I did notice that the original cam had a nearly flat exhaust lobe on one cylinder. The last cam died the same way but faster. Both times I used clevite bearings. The first time a street/strip (from what butler performance said) and the other bearings I got from Summit and were a stock replacement.

When I first replaced the cam and bearings I noticed that the stock bearing fit really snug on the cam's bearing surface whereas the new clevite bearings fit on really sloppy. I'd say that there is about 3 times the clearance. I know this is dropping oil psi. and causing my valvetrain problems but not sure how to solve it.

I have been told by a local well known engine builder that there may be 3 different cam bearing sizes for 400 ci. Pontiac engines. He wasn't sure which engines had what or what year etc. I have never heard of such a thing and have read everything Pontiac related that I could in the last 20+ years.

Has anyone ever heard of such a thing? One other thing I notice about the engine is when I replaced the timing chain (which is the only part of the engine that I could tell had been apart before I took it apart) the new one was just as sloppy as the old one. I have been told that some blocks are machined to closer tolerances than others explaining my slop in the chain.

So, I'm confused. The bearings seem to be consistently the same size and cams bearing diameter seem to be consistent.... even in comparison to the original cam which I still have. I'm about rob some bearings out of another engine I have sitting around. I'm kidding but I'm about that frustrated. Hate half assing things. Thanks, Nate.

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Old 02-27-2012, 05:40 PM
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Are you putting the bearings in the correct location? I assume there are different cam bearing bore diameters and corresponding bearing sizes to match, same as a SBC, but I doubt you could pound the large bearing into the small bores...just throwing that out there.
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Old 02-27-2012, 11:49 PM
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A couple possibilities...

Quote:
Originally Posted by ztwntyn8
I have a 1971 Pontiac 400 which I have replaced the cam and bearings in twice now. The first time for more power and the 2nd because a lifter mushroomed and took a lobe with it. I did notice that the original cam had a nearly flat exhaust lobe on one cylinder. The last cam died the same way but faster. Both times I used clevite bearings. The first time a street/strip (from what butler performance said) and the other bearings I got from Summit and were a stock replacement.

When I first replaced the cam and bearings I noticed that the stock bearing fit really snug on the cam's bearing surface whereas the new clevite bearings fit on really sloppy. I'd say that there is about 3 times the clearance. I know this is dropping oil psi. and causing my valvetrain problems but not sure how to solve it.

I have been told by a local well known engine builder that there may be 3 different cam bearing sizes for 400 ci. Pontiac engines. He wasn't sure which engines had what or what year etc. I have never heard of such a thing and have read everything Pontiac related that I could in the last 20+ years.

Has anyone ever heard of such a thing? One other thing I notice about the engine is when I replaced the timing chain (which is the only part of the engine that I could tell had been apart before I took it apart) the new one was just as sloppy as the old one. I have been told that some blocks are machined to closer tolerances than others explaining my slop in the chain.

So, I'm confused. The bearings seem to be consistently the same size and cams bearing diameter seem to be consistent.... even in comparison to the original cam which I still have. I'm about rob some bearings out of another engine I have sitting around. I'm kidding but I'm about that frustrated. Hate half assing things. Thanks, Nate.
Hi Nate, I seem to recall you've posted about this before... but in any event, the cam bearings themselves do not- generally speaking- cause cam lobe failures.

That said, if there is a problem w/the journal to bearing oil clearance, or the cam bearings are installed incorrectly, or the bearings themselves are incorrect, or the cam tunnel diameter is out of spec, or the tunnel not straight there can be problems.

Are you installing the bearings yourself? If so, do you have the correct tool that locates off the tunnel so the bearings are started straight? Installing the tapered edge (if present) inward? Holes aligned right?

Is the cam tunnel straight? Personally I've not had any that were out far enough to require honing, but I HAVE had to carefully clearance the installed bearings (only a couple times, but still... ) to get the cam to turn as freely as I wanted it to. Needing honing is certainly not unheard of, some blocks supposedly had the bearings honed to fit the cam, so installing replacement bearings could result in an out of spec tunnel.

To start with, I'd recommend you measure the cam, bearings and cam tunnel of the block to see exactly what you have going on. For instance, if the cam tunnel was line honed this can cause the bearings you have to be a loose fit.

Some dimensions you can use to check what you have (from the King bearing site):

Part Number CS 511BB STD
For 1963-79 Pontiac engines only.
Cross reference- ACL: 5C292 CLE: SH- 292S DUR: P-4 FMO: 1220M

Positions 1 through 5

cam journal diameter- 1.8992"/ 1.8997"

cam tunnel bore- 2.0297"/ 2.0317"

cam bearing length- 0.6800"

maximum wall thickness- 0.0644"

You can see from the specs above the cam bearings are basically identical, your buddy might be thinking of the SBC.

Are you sure the cam break in procedure is correct? If it isn't, no amount of working over the cam bearings will ever get the cam to break in right. More on cam break in HERE. If there was one thing that I could stress besides using break in oil/oil additives and cam break in lube on the lobes and lifter bottoms, it would be NO IDLING FOR THE FIRST 15-20 MINUTES! Next to that, you have to be sure the lifters rotate as soon as the engine fires. The lifter bores need to be cleaned of all varnish, this can take a shotgun brass bristle brush w/acetone as a solvent. Usually honing is not needed, and if the bores measure good, don't hone anyway. Do be sure there's no burrs at the top or bottom of the lifter bores or the oil gallery holes inside the bores.

Also be sure you don't have Chevy lifters. A Pontiac lifter will have the oil band beginning ~1.125" up from the foot. A Chevy lifter will be ~0.875".

The push rod length needs to be correct as well. If you are using the bottle neck studs and nuts torqued to 20 ft/lbs, this is especially important because if the p-rod length isn't correct you can't adjust the preload unless you have straight studs and polylocs or adjustable nuts on the bottle neck studs (something I personally never recommend).

If you're using 1.65 ratio rockers, the pushrod hole in the head likely needs to be opened up, otherwise the p-rod can bind.

The valve springs need to be correct for the cam, if the cam is radical enough to require double springs, removing the inner spring during break in is a good idea. HERE is a list of valve train points to check.

There is more but this ought to give you a start.

EDIT- If the crank saddles were line bored and honed, the distance between the c/l of the cam and crank can be closer than it was originally. This requires a different timing set to compensate if it's severe enough.

Last edited by cobalt327; 02-27-2012 at 11:58 PM.
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Old 03-01-2012, 07:55 PM
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Thanks for the good info. I am installing the bearings myself with a universal cam bearing instalation tool. I was very careful to mark the bearing so that the hole is lined up as close to perfect as possible. I am a professional mechanic however, I don't know everything but try to be as informed as possible.

Break-in:
-Cam has all of the lube they gave me in the kit on cam and lifter bottoms.
-As soon as it fired I made sure it stayed around 2k rpm... a little higher than the fastest fast idle setting.
-The engine stayed at that rpm fluctuating only slightly when I was checking timing and making sure all of the push rods were spinning.
-All push rods were spinning.
-Oil was not squirting on the wheel wells. Rather it was oozing out of the rocker arms. I am used to oil squirting all the way to the wheel wells from the rocker with valve covers off and that's at idle not 2K rpm.

As for the different cams:
-stock has the same size bearing diameter as the other summit cams.

Cam bearings:
- all that I have ordered (3 sets now) are the same diameter.
-the replacement bearings fit much much more sloppily compared to the ones I removed form the engine.
-the cam turned much much more freely whith the new cam bearings. Almost no effort at all in comparison to trying to turn the stock cam in the stock bearings.

Engine:
-started with me stock down to brake linings and original exhaust you could put you hand around, showing 43,800 mi. on the clock. No machine work ever. The cyl walls still had cross hatch patterns with no obvious wear.

Car:
- 1971 Formula 400.
-Ram Air heads and cam
-3.42 posi
-TH 400
-13.50@104... till cam later died.

I'm wondering what the clearance should be. The clearance is so much larger with the new compared to the stock bearings that I know it's bleeding allot of oil psi. The second cam died much quicker and I used Rhoads lifters that actually bleed off to help vacuum with larger cams (which both I have installed are within the accepted spectrum of the stock replacement springs.

Thank you for your interest and input.
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Old 03-01-2012, 08:50 PM
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To clarify, Ram Ari III #48 heads and summit blueprint HO, RA III, or 068 cam. It's good idle to 5K rpm. I usually shift around 5200 but it pulls to 6K rpm hard not dropping off if you aren't watching the tach.
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Old 03-02-2012, 08:34 AM
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All Pontiac V8s use the same cam bearings, '55-'81, and all are the same bearing, regardless of "position" (I never understood why more didn't use the same approach, "Lima" (385 Series) Ford being one that did). The "line" from '63-on involves the older "through the stud" oiling for rockers and the later "through the pushrods". Some of the brands eliminated the two "extrra" holes that would feed pressure to the heads. Oil "oozing" out of the rockers while running is correct. Oil "squirting" indicates either worn rockers or worn pushrods or both.

Seldom does the Pontiac have a "bad" cam bore. We see it with 455s more than others, due to the excessive stroke and high stress at lower speeds (tremendous low-end torque, "flimsy" block). I can't recall the last 400 I saw with cam bore issues.

Clevite and Sealed Power bearings are okay for moderate spring pressures. DuraBond are "the good stuff". P-4 is the "standard" bearing and PP-4, the one for higher spring loads (good to 300 lbs. seat pressure).

A "sloppy" timing chain is a problem. If you're certain the block's never been align-bored or honed, there's "something wrong with this picture". Pontiacs, like Olds, were machined to very "close" tolerances from the factory. We seldom see an issue with the main tunnel, squareness of decks, etc. The most common issue we see is another shop align-honed one "wrong", when it probably didn't need it in the first place. Installing studs will NOT distort the main bore like it may in other engine families, the main caps being "doweled" instead of "registered" is the reason. This is also why the Pontiac enjoys such a strong bottom-end when quality parts are used. At very high power levels, "cap walk" is a non-factor.

Make certain your valve springs are correct for the application. Make sure to follow the break-in proceedure as outlined by your cam grinder. If that includes removing the "inner" springs, REMOVE THE INNER SPRINGS!!! Pop always said: "When all else fails, follow instructions..." What is the seat pressure? Nose pressure? You didn't, by chance, change to 1.65:1 rocker arms?

48s are not "Ram Air" heads. That name is "reserved" for large-valve (2.11/1.77), "small chamber" (72, advertised) and ROUND exhaust ports. 48s are good heads, but have "d-port" exhaust. And yes, were installed on '69 "Ram Air" engines with 366 HP. They were also on "non-Ram Air" 350HO engines and 350HP 400s, as well as 375 and 390 HP 428s. Don't worry, this is a common area of misnomer. The same is true of the 1970 casting no. 12. '68 "Ram Air II" (casting #64), '69 (744) and '70 (614) Ram Air IV engines are the only ones equipped with "Ram Air" heads. '71 and '72 had "HO" heads (round port) and '73-'74 were "Super Duty". The 455 heads have HUGE combustion chambers (101-124, depending).

Using the '69 engine, if you haven't taken steps to lower the static compression to under 9.5:1, you ARE experiencing detonation if using 93 octane or lower. We "dish" the pistons to accomplish this. Once that's done, the 068 cam is going to be inadequate. It "likes" higher compression.

FWIW

Jim

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Old 03-02-2012, 02:39 PM
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I agree that I have"D" port heads although, a RAM AIR III engine is a "D" port engine so, not sure why you say they aren't RA III heads. Enough of the semantics.

The only evidence of the engine being apart before I took it apart was marks on the timing cover where the chain had been replaced.

I have stock rockers, push rods and valve springs. I used a summit blueprint HO or 068 cam the first time.

I just don't get why the all of the bearings that I have bought feel so much sloppier than the original bearings that I removed when I have them in my hands and place them on the cam which is also in my hand and that is the stock cam and the summit cam. So, the camshaft's bearing surface is the same diameter stock vs. summit. The bearing it's self has a much larger diameter in the replacement Clevite SH-292S vs. the original bearings that I removed when the engine was all stock.

Any oldschool hotrodder that I ask says they are surprised that I have any oil psi. I was reluctant to put the new bearings in long ago when I did the first cam swap.


Thanks, Nate

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Old 03-02-2012, 03:32 PM
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Quote:
Originally Posted by ztwntyn8
I have a 1971 Pontiac 400 which I have replaced the cam and bearings in twice now. The first time for more power and the 2nd because a lifter mushroomed and took a lobe with it. I did notice that the original cam had a nearly flat exhaust lobe on one cylinder. The last cam died the same way but faster. Both times I used clevite bearings. The first time a street/strip (from what butler performance said) and the other bearings I got from Summit and were a stock replacement.

When I first replaced the cam and bearings I noticed that the stock bearing fit really snug on the cam's bearing surface whereas the new clevite bearings fit on really sloppy. I'd say that there is about 3 times the clearance. I know this is dropping oil psi. and causing my valvetrain problems but not sure how to solve it.

I have been told by a local well known engine builder that there may be 3 different cam bearing sizes for 400 ci. Pontiac engines. He wasn't sure which engines had what or what year etc. I have never heard of such a thing and have read everything Pontiac related that I could in the last 20+ years.

Has anyone ever heard of such a thing? One other thing I notice about the engine is when I replaced the timing chain (which is the only part of the engine that I could tell had been apart before I took it apart) the new one was just as sloppy as the old one. I have been told that some blocks are machined to closer tolerances than others explaining my slop in the chain.

So, I'm confused. The bearings seem to be consistently the same size and cams bearing diameter seem to be consistent.... even in comparison to the original cam which I still have. I'm about rob some bearings out of another engine I have sitting around. I'm kidding but I'm about that frustrated. Hate half assing things. Thanks, Nate.
Are the cam bearings being installed with the correct orientation which is the oil hole in the bearing shell matches the oil hole in the block which would put the oil hole almost in the 6 O'clock position. If this is off, the cam bearing will starve for oil. Probably the reason Pontiacs and Oldsmobiles are know to spin these bearings on rebuilt motors.

If your concern that the clearance is too much you can use the same Moroso restrictors that were talked about here on an Oldsmobile thread a few weeks ago. But, be careful at the number 1 main that the restrictor goes into the cam bearing feed hole not the passage that feeds the opposite side's lifters. Also be careful that restrictors are well seated so they don't obstruct the transfer passage which would reduce oil flow to the mains.

It is not likely that oil flow to the cam bearings would affect lobe and lifter life. Unfortunately flat tappet cams are suffering these days with low quantities of ZDDP in the oil. This is a big disadvantage to engines running fast lift rate cams and high spring pressures or even incorrectly light pressures for the cam being used as this can cause the spring to loose control of the valve train resulting in the lifter slamming down on the lobe with considerable and unusually high force. Most cam lobe to lifter lubrication comes from crank throw-off. Therefore, one also needs to maintain an idle speed high enough to keep plenty of oil flying into the cam.

Bogie
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Old 03-02-2012, 04:50 PM
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Quote:
Originally Posted by ztwntyn8
I agree that I have"D" port heads although, a RAM AIR III engine is a "D" port engine so, not sure why you say they aren't RA III heads. Enough of the semantics.

The only evidence of the engine being apart before I took it apart was marks on the timing cover where the chain had been replaced.

I have stock rockers, push rods and valve springs. I used a summit blueprint HO or 068 cam the first time.

I just don't get why the all of the bearings that I have bought feel so much sloppier than the original bearings that I removed when I have them in my hands and place them on the cam which is also in my hand and that is the stock cam and the summit cam. So, the camshaft's bearing surface is the same diameter stock vs. summit. The bearing it's self has a much larger diameter in the replacement Clevite SH-292S vs. the original bearings that I removed when the engine was all stock.

Any oldschool hotrodder that I ask says they are surprised that I have any oil psi. I was reluctant to put the new bearings in long ago when I did the first cam swap.


Thanks, Nate
Measure the oil clearance of the cam journal to cam bearing by fitting the bearing onto the block, then measure the cam bearing ID then compare this to the cam journal OD. You want at least 0.002" to 0.003" (0.004" max, high performance use) clearance w/the cam turning easily.

Because aluminum alloy bearings are harder and less forgiving to can tunnel misalignment than babbitt overlay bearings, there is a possibility the aluminum alloy cam bearings are intentionally larger.
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Old 03-02-2012, 06:48 PM
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Because aluminum alloy bearings are harder and less forgiving to can tunnel misalignm

This sounds like my best bet so far. A sprint car guy said that maybe the bearings would change diameter as they were pressed into the block but another guy said if it shrunk that much it would prob need align-honed. I realy don't think I have any wierd block issues etc.

Some of these people think that larger than normal tolerances wouldn't hurt lifters or cam because it may not be directly feeding the lifters but any psi. drop is a a drop accross the board.

Thanks for turning me onto measuring a pressed in bearing. I will try that.
Nate~
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Old 03-14-2012, 10:04 PM
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Measure the oil clearance of the cam journal to cam bearing by fitting the bearing on

My friend who is a toolmaker is out of town and if the measurement needs to be that accurate, I want him to do it.

Tonight I pulled the cam out of my 73 455 TA (71 Formula is to other) which I have previously installed stock replacements from summit and same part # as the ones that I last installed in the formula's 400. When I got the cam out (only after break-in for 20 min. (and this was last year but not started since) and the cam bearings themselves were scored in from the 6 o'clock postion to the 12 o'clock. The one bearing that I didn't replace (that I couldn't unless I pulled the engine and it wasn't scratched by the cam comming out by the dist drive gear) looked realy evenly worn compaired to the new bearings. All new bearings were worn irradicaly. It was already digging into the bearing. I can't feel it but can def see it.

I also tried the cam in the front most bearing on the way out and I can feel the same slop that I can when I test an uninstalled bearing on the cam. I'm fairly certain that I have a tollerance issue.

I'm about to order bearings from another co. and see what I get. I guess they are cheep enough it's just spending the couple hrs. to get to them.
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Old 03-15-2012, 08:44 AM
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I just went through the "exercise" of measuring all these things.

Cam tunnel holes measure 2.298" (three different blocks, all within .0003" of each other). OD of uninstalled bearing is 2.030-2.031" (stock type, same with "performance"). Installed, ID is 1.900" "on the nose". Cam journals on two NEW cams are 1.898".

When the bearing is installed, the "crush" of .002" reduces the ID to the correct size. The "interference' fit is required to keep the bearings "in place". I have never seen a Pontiac "turn" a cam bearing. Olds and Buick? Yes. A 455 Buick will wipe the cam bearings out in a couple of minutes if not properly installed or the engine is overheated.

Minor scratches on cam bearings is not a big concern. From a strictly technical POV, they're not really "bearings" per se, but "bushings".

Restricting oil to the cam bearings is not a typical "modification" done to Pontiacs. SOME builders will "block" the passage when roller cam bearings are used (lubed by "splash").

Semantics are not the "issue" with the d-port heads. It is very misleading to call the d-ports "Ram Air" because it confuses them with "real" Ram Air heads. As a Pontiac guy, I want accurate info "out there". It's hard enough to get folks over the "rod issue", much less all the misnomers.

FWIW

Jim
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Old 04-06-2012, 04:48 PM
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Right on Jim. Now I have some measurements to compair to. I still need my buddy to stop by or get some good calipers or mics myself.

Yeah, I realize they could be 350 HO heads. I was just trying to discribe my combo. I guess the RA III is the only "Ram Air" engine that has D ports huh. That's kinda a trip. I guess that was more of a marketing strategy?

I'm gonna get after it this weekend. Have a good weekend.
Nate
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Old 04-20-2012, 06:46 PM
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I just went through the "exercise" of measuring all these things.

Ok, I had engine builder from the 60's and 70's came by my body shop yesterday. Today he showed up with inside and outside mics. It seems that my out of the box vs installed and then removed or "crush" is .006 OD. He was concerned and I asked shouldn't it be about half that. He said yes and was concerned. He went to the shop he used to work at and took my engine info with him. He says that my OD on the bearings is correct and measured my block's bore for the cam bearing and said that they were fine. The thing he didn't like is that the replacements were skinnier. As in they don't cover as much of the bearing surface. I think I remember the stock bearings being wider.

His concerns are all about my oil psi. Obviously if my crushed ID is too big it will bleed off psi. and kill everything. I can't believe we didn't measure the id. of the installed bearing or even the uninstalled bearing. I just forgot to mention it because I was trying to shut up, respect and learn from him.

This guy is in his mid 70s but he looked realy confident with measurements and took his time but it didn't take him long.

His measurement on the uninstalled OD was 2.035.5" He verbaly said 2" and 35 and a half thousandths and to put a decimal point there. I supose it was a significant digit sort of thing but that was his way.

The installed bearing OD was 2.029.5"

So, there is .006" difference in OD but not sure about ID.... dang it.

When he had the installed in his hand measuring he laughed as he remembered the cam journal size and said "I could probably put this in with my hand" and walked over and put it about 1/4" in by hand. Then thought about how much it is crushing and said that is way too much.

Then he wanted to see my instalation tool.... It's a universal with an expandable center made of 4 pieces and a rubber 1/8" rubber sleeve that contacts the ID of the bearing. He said that the ones he used were metal. I asked the obvious about the rubber giving and letting it crush too much. He nodded as in yes but not too quick to say that's the problem.

He asked me about the heads and springs. The blueprint 068 had that small barely over .400 lift and think that's why it lasted longer but the summit 2802 cam has .488 or so lift and he is concerned aobut coil bind. My cam card was blank where the recomended springs place is. I was told and accepted the idea that stock springs are good up to .500 lift. Since I had one lifter fail.. not all of them he said that he suspects coil bind on that spring or possibly valve touched a piston bottoming the lifter and destroying the cam. He was also realy concerned about breakin. Saying that if 1 lifter or lobe is scared it will fail. So, I have alot to think about. Also, he said that the tolerances aren't always that great and that if I had the original bearings they would have been marked as to how much larger or smaller they were to accomadate the cam journals. Keep in mind he was a builder of ford, chrysler, pontiac, chevy, honda. Which brings me to another tolerance learning experience. He said Honda auctualy measures to tenths of thousandths and can have several different sized main bearings according to the colored markings and if you were to install all the same sized replacement bearings the engine would run but wouldn't last nearly as long as if they were more precise.

He also told me that with the thousands or so engines he has built that ones like mine that were running well before a build typicaly had more problems than a worn out engine that auctualy has to be rebuilt. I see that now since now you have new machine work and you get bearings etc. that match the new cut. That makes alot of sence.

Told me one other thing I want to share. On a ford road race engine he was having problems with them lasting and a known ford guru built an engine with him. I think he said the rods had .004" clearance and mains .006"....... could be vice versa but much larger than what he is used to. He also said that you can block the bypass on the oil pump which they did. Had to use a special oil filter so it wouldn't blow off. The psi. was 200 lbs! and once the engine warmed up it ran at 35 psi. He said he couldn't believe it but it worked many years ago and is still capable of running but is sitting under a bench.

IDK, but I think he can get me straitened out. I may buy a pro cam bearing instalation tool but still want the factory replacement bearings and to instal correctly. I'm going to post pics of the 455 that didn't fail but was broken in for 20 min. @ 2000 and you won't believe the amount of wear on the cam bearings in that amount of time. It was (goiong clockwise) half of the bearing scored and worn from 6 o'clock to 12 o'clock pretty bad concidering the run time. He also said it should if anthing wear in the bottom half not one side. I'm still trying to process all of this and make scence of it. I think I'm going in the right direction though. Thanks for the help. I have been realy frustrated and have 2 cars down over this ****. Anyway, if you have any differences in opinion lmk. Thanks again, Nate.
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Old 04-20-2012, 09:37 PM
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As far as writing the measurements, you can leave off the second decimal point, it's not needed. The place of the number to the right of the first decimal point gives the value for that digits place, i.e. tenths, hundredths, thousandths, ten thousandths (sometimes called "tenths" when taking precision measurements, i.e. 0.0003 would be "three tenths" to machinists, etc. who understand that it doesn't mean 0.3).

It's common to call 0.0055 "five and one half thousandths" instead of "55 ten thousandths", or 0.0053 is "five point three thousandths" instead of "53 ten thousandths" though (even though either is correct, technically speaking), and maybe that's what he was trying to get across.

About the cam bearings, I have been told that Pontiac block cam tunnels were drilled first from one end, then from the other end, meeting somewhere in the middle. If that's really the case (I never saw a factory Pontiac block machining line or talked to anyone who worked on one to know for sure), there could easily be a mismatch. What I was led to believe is that the cam bearings themselves were align bored/honed after they were installed to get a straight cam tunnel. That would mean the original bearings could be thinner on one side than the other to compensate for any misalignment, if you follow me. And THAT would mean in cases where the misalignment was more than the oil clearance, there could be contact between the cam bearing journal and the cam bearings if the bearings were concentric (same thickness all the way around).

This could also account for the bearings being made "loose"; in order to compensate for the possibility there was a misalignment, extra ID was made into them rather than having the bearings "tight" and risk the cam bearings spinning or rapidly wearing in service.
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