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alsadler 08-08-2012 11:06 AM

283 with 305 heads
 
Having an issue with it not running right. Rebuilt carb, new distributer and vacuum lines. Still not right. Took of timing cover and gears were at 12 oclock on them both. When I rotated this top gear it sounds like I hit the top of the piston with the valve when the dots lined up. Any ideas?

oldbogie 08-08-2012 12:17 PM

Quote:

Originally Posted by alsadler (Post 1581135)
Having an issue with it not running right. Rebuilt carb, new distributer and vacuum lines. Still not right. Took of timing cover and gears were at 12 oclock on them both. When I rotated this top gear it sounds like I hit the top of the piston with the valve when the dots lined up. Any ideas?

Timed correctly the Chevy needs the crank gear in the 6 O'clock position and the cam gear in the 12 O'clock. This brings the engine ready to fire number 1 with the cam correctly coordinated with the crank. At 360 degrees of rotation from that point the crank gear would be in the 12 O'clock position and the cam gear right across from it at the 6 O'clock position. At this point it is set up to fire number 6 and the cam and crank are coordinated.

You need to open up the timing cover and get the gears into one of the configurations I sight with the distributor pointed at the appropiate cylinder for firing.

Bogie

alsadler 08-08-2012 01:42 PM

No 1 is at top dead centre right now with the crank dot at 12 oclock, with the cam dot at 12 oclock the valves were both closed. The timing chain instructions show that both marks should face each other. If the crank was at 6 oclock the piston would be on the bottom not the top. Is that not how it should line up with the piston at the top and both valves for No 1 loose?

oldbogie 08-08-2012 01:51 PM

Quote:

Originally Posted by alsadler (Post 1581169)
No 1 is at top dead centre right now with the crank dot at 12 oclock, with the cam dot at 12 oclock the valves were both closed. The timing chain instructions show that both marks should face each other. If the crank was at 6 oclock the piston would be on the bottom not the top. Is that not how it should line up with the piston at the top and both valves for No 1 loose?

The instructions are wrong.

Bogie

alsadler 08-08-2012 02:00 PM

ok thanks for the info!

oldbogie 08-08-2012 03:37 PM

Quote:

Originally Posted by alsadler (Post 1581177)
ok thanks for the info!

Sorry for being so abrupt and I need to admit to an error. I was in the middle of adding a correction and qualifier when I was interrupted with work problems in the shop.

Timing the Gen 1 Chevy is kind of tricky and many instructions and certainly several locations on the web don't tell you all you need to know. Well at least it isn't a Ford Y block where you have to count 12 pins in the chain between the timing marks that are horizontal to the ground and facing the driver’s side of the vehicle.

When the Gen 1 SBC is set up with the marks facing each other, crank at 12 and cam at 6 the cam and crank are coordinated, number one is coming off exhaust and preparing to intake. Number 6 would be a TDC firing both valves tightly closed.

I'm not introducing the idea of ignition advance to keep things simple everything I'm meaning here are events at Top Dead Center. The engine can actually be started at TDC the first time then advance adjusted; I mostly do this for the sake of simplicity. As long as you know this position is ready to fire number 6 you can set the distributor up correctly. Many instructions and YouTube videos just don't go that far or miss saying anything about this.

Certainly a way back to number one firing using the pip marks facing each other technique is to rotate the crankshaft one full turn after the alignment which will place both marks at the 12 o’clock position. when I read my original response this points to an error I made where I said to put the crank at 6 and the cam at 12. That should have read crank at 12 and the cam at 12; shows you what rushing does to your thoughts while people are trying to discusss other problems with you while your typing, I find as I'm aging that multi-tasking is a diminishing capability.

So the crank and cam gears at 12 will give the cam and crank coordinated and number 1 on firing. Or with the gears facing each other the cam and crank are also coordinated and number 6 ready to fire. Your comment "No 1 is at top dead centre right now with the crank dot at 12 oclock, with the cam dot at 12 oclock the valves were both closed. The timing chain instructions show that both marks should face each other. If the crank was at 6 oclock the piston would be on the bottom not the top. Is that not how it should line up with the piston at the top and both valves for No 1 loose? " ..... is correct. This engine should be ready to fire timed at number 1.

I apologize for my error and abruptness.

Bogie

cobalt327 08-08-2012 04:49 PM

Quote:

Originally Posted by alsadler (Post 1581135)
Having an issue with it not running right. Rebuilt carb, new distributer and vacuum lines. Still not right. Took of timing cover and gears were at 12 oclock on them both. When I rotated this top gear it sounds like I hit the top of the piston with the valve when the dots lined up. Any ideas?

Here is a page w/info on how to properly install a distributor.

Be aware that there are several different timing tabs and TDC damper lines used through the years. Here is a page showing the differences.

To be sure we're on the same page, w/the cam gear dot at 6 o'clock and the crank gear at 12 o'clock (dots closest to each other as is physically possible), cylinder #6 is ready to fire. If the distributor were to be installed at this point, the rotor would be pointing to terminal #6 of the distributor cap.

With the timing gear dots (cam AND crank) both at 12 o'clock, #1 is ready to fire. If the distributor were to be installed at this point, the rotor would be pointing to terminal #1 of the distributor cap.

What I'm the most concerned about is the possibility of interference between the piston and valve at or near TDC. You must correct this if it exists, else severe damage will result!

Some common causes for there to be a valve and piston too close or touching:
*incorrectly phased camshaft
*too much valve lift
*incorrectly adjusted valves- and this is easy to get wrong unless you are used to adjusting valvers and finding the "zero lash" position. Often the books say to twist the pushrod between the fingers and thumb to feel when zero lash is reached. Doing it this way often results in the bottoming of the lifter plunger as being mistaken for zero lash. Then when the additional hydraulic lifter preload is added, this in effect lifts the valve up off the seat which will result in no compression and no start. It also can cause the valve to be too close to the piston.

The better way to feel/look for zero lash is to jiggle the pushrod up and down. This helps by being able to both feel and hear when zero lash is reached.

Some links to info:

Cam installation tips

Adjusting hydraulic lifters

Valve train areas to check

HEI distributor info

Determining TDC

Prep and start a new engine

alsadler 08-08-2012 07:53 PM

That is the way it was origionally but it did not want to even idle. Had to drive with two feet. We did set it to six and 12 and it did start but only once then it stalled and we could not get it started. does not seem to be timed right eather way, but tommorrow is another day.

jaded13640 08-09-2012 05:56 AM

Piston sounded like it hit the valve?
 
My concern is that if in fact it was running, even for a second, AND you actually did have that piston touch the valve, it's bent.

You'll certainly want to correct the cam timing if the gears are aligned incorrectly but I would do a compression test before even starting it again. If you have any bent valves you'll likely read zero cylinder pressure on any cylinders that have bent valves. If a valve is only very slightly bent it may build some pressure but will probably be much lower than the rest.

I always check piston to valve clearance when building a motor. Especially if I'm using a different cam or heads or both than it had before the build.

Good luck and I hope your valves aren't bent.

Wayne

bullheimer 08-10-2012 12:43 AM

wow after reading this i am beginning to wonder if i ever built an engine before. i cannot believe cobalt327, who i KNOW has built like ten million engines or something, is saying exactly what old bogie said, and that is that the gear marks with them as close as possible to each other (6/12) is for #6. i have always thought, and installed them in engines that ran, this position fires #1. is today april first or something? or did gear manufacturers change where they are putting their marks? i am definitely subscribing to this to get an explanation on this thing.

i, sitting here on my happy hole, say i am positive its #1. but that said, get ready for bent valves. i would do that compression check. then take everything apart again and start from scratch. sucks, but, tough break. make sure that if you have a circle gear mark, a square or triangle, and an oval (zero), on the cam gear, that you did not mistake the zero for the circle. i did that once and got the same result as you, except the engine wouldnt start.

the california kid 08-10-2012 01:38 AM

al sadler

here's link

How To Install A Camshaft - Tech Article - Chevy High Performance Magazine

timing gears are about the 5th paragraph and

there's some other neat stuff in there.

beats me what a Voodoo cam is but

Speedomotive goes way back.

have a nice day

jaded13640 08-10-2012 01:57 AM

bullheimer. That's exactly what I thought. The marks face eachother (crank mark at 12 o'clock and the cam at 6) and that is top dead center on the compression stroke for the number one cylinder.

However, my only chevy engine build experience is with big blocks and without even considering otherwise I installed the gears with the dots facing each other.

I'm really not following why GM would have you set the marks up at 12 and 12 and have that be number 6 at TDC. I just doesn't seem to make any sense to me.

Wayne

F-BIRD'88 08-10-2012 02:40 AM

If you were to actually read the cam install directions.

Line the dots up 6 and 12 when installing the cam and cam gear and chain.
Then rotate the crank shaft 1 turn.
Now the dots are 12 and 12 oclock.
Now the engine is at TDC fireing #1.
Now install the distributor with the rotor pointing to #1 on the cap.
Real simple when you read the cam install directions.
But who reads instructions.

jaded13640 08-10-2012 10:22 AM

I did read. Actually even.

I'm not disputing what the directions say or what is the correct way to do it is. My point is that it seems odd.

I just don't follow why GM didn't just have the marks line up at the closest point and THAT be #1 TDC.

However, I know why they do things like that sometimes. For example the Chrysler V6 that was a 318 with two less cyclinders employed something like that. When the teeth were lined up it was not at #1 TDC. I understand why that happened because they took an existing design, modifyed it and all the same design specs, just a shorter block, crank, heads etc. Great for reducing design costs, bad for things being done as they normally are.

Did GM make a change that brought about this or had that application always been that way?

Wayne

oldbogie 08-10-2012 10:52 AM

Quote:

Originally Posted by jaded13640 (Post 1581694)
I did read. Actually even.

I'm not disputing what the directions say or what is the correct way to do it is. My point is that it seems odd.

I just don't follow why GM didn't just have the marks line up at the closest point and THAT be #1 TDC.

However, I know why they do things like that sometimes. For example the Chrysler V6 that was a 318 with two less cyclinders employed something like that. When the teeth were lined up it was not at #1 TDC. I understand why that happened because they took an existing design, modifyed it and all the same design specs, just a shorter block, crank, heads etc. Great for reducing design costs, bad for things being done as they normally are.

Did GM make a change that brought about this or had that application always been that way?

Wayne

Gen 1 SBC has always been this way where the pip marks facing each other is cam and crank coordinated, both number 1 and 6 are at TDC but 1 is ready to intake and 6 is ready to fire. So with the marks in this position the distributor is dropped in with the vacuum can in the normal position but the rotor set to number 6.

However, always read the instructions with an aftermarket timing set, while I haven't seen one where the marks pointing at each other (like a SBFord) is number 1 firing, there's always the possibility that some one struck out on their own ideas about this.

If you think this is fun try a Harley twin cam where the pip marks on the cam to cam gears are on the inside and can't be seen without a mirror or pulling the outer cam bearing plate with cams out of the engine. You ask who thinks this stuff up? Beats me, but they have a perverse sense of humor. Remember the old International V8 that times off number 3? Plus I previously mentioned the Y-Block Ford with 12 chain link pins between the gear marks with the marks parallel to the ground and facing the drivers side (American). If anyone is looking for logical and simple this ain't the place to find it.

Bogie


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