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Old 01-24-2013, 04:42 PM
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SBC OEM Hyd Roller Thrust issues

Okay I'm stumped. This is what I have. I have a 350 block out of a 1991 pickup that was originally flat tappet. It has the provisions for the oem roller setup so I got a oem style roller cam from howards with the stepped nose. (180325-08). I currently do not have the rear cam plug in the block. The cam moves freely back and forth without the timing gear attached. This is the timing set im using Summit Racing® True Roller Timing Sets SUM-G6601 - SummitRacing.com. Its for an OEM roller setup for a NON vortec engine.

I know the last picture is a tad fuzzy but you can see the nose of the cam sticks out about an 1/8". The recess in the timing gear is about an 1/8th" as well.

Here is my problem.... It seems as though when I tighten down the timing gear it sandwiches the thrust plate between and draws the timing gear and cam together and eliminates any thrust clearance I have.


What am I doing wrong.... any ideas?

Thanks for your help everyone!

,Shane



Edit: Also this motor was run for about 50 miles with the clearance issues. Wear can be seen on the thrust plate and thrust surface on the timing gear.
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Old 01-24-2013, 04:52 PM
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Quote:
Originally Posted by zildjian4life218 View Post
Okay I'm stumped. This is what I have. I have a 350 block out of a 1991 pickup that was originally flat tappet. It has the provisions for the oem roller setup so I got a oem style roller cam from howards with the stepped nose. (180325-08). I currently do not have the rear cam plug in the block. The cam moves freely back and forth without the timing gear attached. This is the timing set im using Summit Racing® True Roller Timing Sets SUM-G6601 - SummitRacing.com. Its for an OEM roller setup for a NON vortec engine.

I know the last picture is a tad fuzzy but you can see the nose of the cam sticks out about an 1/8". The recess in the timing gear is about an 1/8th" as well.

Here is my problem.... It seems as though when I tighten down the timing gear it sandwiches the thrust plate between and draws the timing gear and cam together and eliminates any thrust clearance I have.


What am I doing wrong.... any ideas?

Thanks for your help everyone!

,Shane



Edit: Also this motor was run for about 50 miles with the clearance issues. Wear can be seen on the thrust plate and thrust surface on the timing gear.
What's it's doing in drawing the gear down to the thrust plate is correct, but the gear should bottom its hub (bolt circle) against the cam snout before it binds on the thrust plate. Some thin shim stock between the cam snout and the gear under the bolts should solve the problem by seating the gear before it clamps the thrust plate between it and the cam.

Bogie
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Old 01-24-2013, 05:14 PM
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Originally Posted by oldbogie View Post
What's it's doing in drawing the gear down to the thrust plate is correct, but the gear should bottom its hub (bolt circle) against the cam snout before it binds on the thrust plate. Some thin shim stock between the cam snout and the gear under the bolts should solve the problem by seating the gear before it clamps the thrust plate between it and the cam.

Bogie
Is it common to have to install shims to get the thrust clearance correct? would a different timing set maybe fix this? If im pointing blame at the $30 timing set or the $300 cam im leaning towards maybe trying a new timing set. Any ideas?
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Old 01-24-2013, 06:16 PM
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Is it common to have to install shims to get the thrust clearance correct? would a different timing set maybe fix this? If im pointing blame at the $30 timing set or the $300 cam im leaning towards maybe trying a new timing set. Any ideas?
I can't say this is common.

Looking at the pictures it appears that there is more wear on the top of the thrust plate than the bottom. This could be:
- The block is warped or miss machined across the face.
- The cam thrust face is angled slightly.
- The cam bore of the block slopes going rearward.
- The thrustplate is machined at an angle.
- The gear is machined with an angle.

Without a lot of dissassembly and measurement it's hard to say which of these are the cause. My quick and dirty method would simply measure for .005 inch clearance at the tightest spot, get some brass shim stock that provides that clearance and cut it out to the bolt circle and install it between the cam nose and inside of the gear hub.

I suggest brass as in the paper thin dimension you'll need as it's stiffer than aluminum foil and softer than steel so its strong enough to survive and not crush under the bolt load while soft enough to shape with hobby tools.

Bogie
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Old 01-24-2013, 06:47 PM
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thanks bogie, I have to go to my machinists tomorrow and I will see what he can do for me.
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Old 01-24-2013, 07:20 PM
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If it was mine, I would thin the thrust plate using a plate of glass, 600 grit sandpaper, and WD-40. But that's me.
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Old 01-25-2013, 03:51 AM
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Or lap the thrust face of the cam gear, but that's already been suggested.

If you decide to change the dimensions of anything, first use a straightedge to check the alignment of the cam gear to the crank gear. Then see if moving the gear forward (using shim stock) or moving it rearward (lapping the cam gear thrust face or lapping the retainer plate) brings the alignment of the two gears closer to perfect.

And yes, I know there's some alignment leeway in the width of the chain vs. the widths of the gears. But if you're going to do anything that will affect the alignment, do it to make it better not worse.
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Old 01-25-2013, 07:50 AM
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Or lap the thrust face of the cam gear, but that's already been suggested.

If you decide to change the dimensions of anything, first use a straightedge to check the alignment of the cam gear to the crank gear. Then see if moving the gear forward (using shim stock) or moving it rearward (lapping the cam gear thrust face or lapping the retainer plate) brings the alignment of the two gears closer to perfect.

And yes, I know there's some alignment leeway in the width of the chain vs. the widths of the gears. But if you're going to do anything that will affect the alignment, do it to make it better not worse.
I like that idea. I will first see where the timing gear is sitting with respect to the crank gear and decide from there.
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Old 01-25-2013, 09:07 AM
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If I were you, I'd remove the retainer plate and inspect the other side where the cam nose contacts, and smooth the surface if its galled. It should show similar evidence of contact if the retainer is acting like the meat in a sandwich. If not, it would suggest that the cam was being pulled rearward by distributor, or pushed from front(wouldn't think so if there is enough timing cover clearance)?
You may want to remove the cam, and install the retainer between the gear and the cam for testing to see if there is adequate clearance. It may not be easy to turn the cam in the block and be certain that any resistance is from the retainer/gear/cam interference alone. Just a thought.
FWIW,
ssmonty
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Old 01-25-2013, 10:22 AM
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Originally Posted by ssmonty View Post
If I were you, I'd remove the retainer plate and inspect the other side where the cam nose contacts, and smooth the surface if its galled. It should show similar evidence of contact if the retainer is acting like the meat in a sandwich. If not, it would suggest that the cam was being pulled rearward by distributor, or pushed from front(wouldn't think so if there is enough timing cover clearance)?
You may want to remove the cam, and install the retainer between the gear and the cam for testing to see if there is adequate clearance. It may not be easy to turn the cam in the block and be certain that any resistance is from the retainer/gear/cam interference alone. Just a thought.
FWIW,
ssmonty
that makes sense. I will pull it apart this weekend and get you some pics of both sides and the cam face and do some measurements and assembly and see what im working with.
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Old 01-25-2013, 07:57 PM
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I had thought that with your gear bolted on, there was no clearance between the retainer plate and the back (thrust surface) of the cam gear. That would mean there was no "outside force" pushing the cam rearward, instead, there was a problem w/either the depth of the step on the nose of the cam (too short), or the thickness of the gear vis-a-vis the thrust face to the bottom of the bore that the stepped nose of the cam fits (too much), or the thickness of the plate (too thick).

In going over our previous conversation on this, I see you measured the cam retainer plate at 0.100", and the step on the cam nose at 0.260".

That leaves the step of the cam nose 0.160" proud of the retainer.

That means the depth of the cam gear has to be an amount less than 0.160" or there will be no clearance for the thrust surface of the gear to the retainer. I don't recall you giving the depth of the gear when we talked about this earlier.

Or to put it another way, w/the cam out and the retainer on the step and the cam gear bolted to the cam, the plate should be free to turn w/about 0.010"-0.015" clearance.

The face of the block doesn't matter as far as how far forward the face is, the cam will move to compensate because it's free to float fore/aft as needed (within reason, obviously). It should be square, however, and the wear pattern shows yours to be off a slight amount. But as long as there's some clearance between the gear and plate, the squareness being off a couple minutes really doesn't matter on a street build.
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Old 01-25-2013, 11:14 PM
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One thing I noticed is the galley plug face is flat, just as they are on Vortec blocks. Even so your block is a non vortec, it still could be possible that it will require a vortec type chain. I went and took a look at the face of both my Vortec blocks and they're identical to yours. When I looked at a older 305 block the galley face had the classic high low arrangement. Not saying this will solve the issue, but thought it maybe worth saying.
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Old 01-29-2013, 04:16 AM
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One thing I noticed is the galley plug face is flat, just as they are on Vortec blocks. Even so your block is a non vortec, it still could be possible that it will require a vortec type chain. I went and took a look at the face of both my Vortec blocks and they're identical to yours. When I looked at a older 305 block the galley face had the classic high low arrangement. Not saying this will solve the issue, but thought it maybe worth saying.
I wonder if its worth it to see if my machinist has a timing chain for a vortec that I could mock up real quick to check. I have only seen older blocks, vortec blocks and my block and I would definitely agree that mine looks like the vortec one. Idk what GM did differently between the flat tappet, the pre vortec rollers and then the vortec rollers.

Thanks for the input guys. Sorry took me so long to get back to you Ive been swamped with school and work.
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Old 01-29-2013, 10:42 AM
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Originally Posted by zildjian4life218 View Post
I wonder if its worth it to see if my machinist has a timing chain for a vortec that I could mock up real quick to check. I have only seen older blocks, vortec blocks and my block and I would definitely agree that mine looks like the vortec one. Idk what GM did differently between the flat tappet, the pre vortec rollers and then the vortec rollers.

Thanks for the input guys. Sorry took me so long to get back to you Ive been swamped with school and work.
Couldn't hurt to try a Vortec-specific timing set or at least the cam gear to see if there's a difference.

To help w/the diagnosis, the timing set currently being used is SUM-G6601. Application is '85-'99. It says "For factory roller camshaft Gen 1 motors, except 1996 and later Vortec. Will not fit behind stock plastic timing covers."

The timing set that was mentioned as a possible replacement for the Summit timing set is Cloyes p/n 9-3145. Application is '85-'99. Says "For factory roller camshaft motors. Will not fit behind stock plastic timing covers."

The camshaft is a Howards OE roller.

I have heard of double row cam gears requiring the block to be clearanced, and it's common knowledge the plastic timing covers are a problem. I've also heard the steel cover may need to be replaced or use doubled gaskets for clearance, although I've not had that problem on any I've dealt with. But if the retainer plate is being pinched between the cam gear and the step on the nose of the cam, something's just not right (obviously). It seems like measuring the length of the cam nose step, the depth of the bore in the back of the cam gear where the cam sits, and the thickness of the retainer plate should show what's wrong.

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Old 01-29-2013, 12:18 PM
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I wonder if its worth it to see if my machinist has a timing chain for a vortec that I could mock up real quick to check. I have only seen older blocks, vortec blocks and my block and I would definitely agree that mine looks like the vortec one. Idk what GM did differently between the flat tappet, the pre vortec rollers and then the vortec rollers.

Thanks for the input guys. Sorry took me so long to get back to you Ive been swamped with school and work.
The Vortec is pretty much the same as the other OEM rollers, it adjusts the gears and chain for the plastic timing cover that comes on those engines. It should fit the older roller blocks with the sheetmetal timing cover but the thrust depth should be the same as the camshafts and thrust plates interchange at least insofar as the two different bolt hole distances used between the very early roller blocks and the later ones are concerned.

Still there is no harm in trying different gears to see if a better clearance can be had.

Generally the configurational difference between non roller, roller, roller optioned but flat tappet equipped are:

- Flat tappet blocks have no provisions for a roller i.e. no spider mounting bosses (3), no face machine or drillings for the thrust plate, low height lifter bores, flat face on cam. Thrust is taken between the backside of the cam driven gear and the block face. The cam will always have a fuel pump lobe.

- Roller blocks have three bosses on top of the main oil galley to mount the spider, the block face is machined to accept two mounting bolts for the thrust plate, there is a thrust plate, the lifter bores are raised to provide support for the longer lifter, the lifters are tied in pairs by a gadget called the dog bone, the cam has a stepped face that protudes about 1/4 inch forward of the flat tappet cam so it can pass through the thrust plate, the cam gear is modified in the hub so it can accomodate the thickness of the thrust plate which it now reacts against instead of the block face. The cam may or not have fuel a pump lobe. The push rods are shorter to accomodate the taller roller liftesr.

- Roller provisioned blocks with a flat tappet cam have all the unique provisions for a roller cam but use a standard non roller cam with the flat and short face. This uses standard length flat tappets with the older standard length (longer) push rod. It uses the older timing gear that reacts thrust aganist the block instead of a thrust plate. The cam may or not have a fuel pump lobe.

- The Vortec block used in the L31 Vortec is the same as the preceeding roller blocks whether those blocks had a roller or flat tappet cam. The Vortec block (880) actaully was used in late 1995 production and some 1996 Vans with a flat tappet or roller tappet cam, sheetmetal timing cover, Swirl Port or L31 Vortec heads, with Throttle Body Injection (TBI). Where the L31 in pickups starting with 96 production all used Central Multi-point Fuel Injection, L31 Vortec heads (two versions), a plastic timing cover which drives a unique timing gear and chain set for clearance (narrower gear teeth and chain) because the plastic timing cover accomodates often but not always a built in crank seal and always a crank position sensor.

As you can see where the roller provisioned or equipped and the L31 blocks are concerned there is a lot of interchange between them and they can use the flat tappet cam, lifters and timing set from older Gen I engines when all this stuff comes in a set of equipment. The L31 Vortec plastic timing cover does require a unique narrowed timing set as it uses up space for the crank position sensor. If you're using an L31 Vortec with carb or TBI it's simple back date the engine to use the sheetmetal or even a cast aluminum timing cover from the earlier engines.

Bogie

Last edited by oldbogie; 01-29-2013 at 12:25 PM.
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