Medida

I am completing the build of the engine and it has comp cams stage II cams, Supertech Valves and Valve Springs, new forged piston and connecting rods and balance shaft removal. I purchased a new timing chain, timing chain tensioner guide, fixed timing chain guide, upgraded timing chain guide bolts. Aligned the marks on the intake cam gear, exhaust cam gear and crankshaft gear to the marks on the chain. Compressed the timing chain tensioner and the put it all together. Double checked that the marks were all aligned and then I released the tensioner.

Went to check the cams with a degree wheel and was seeing some "funny numbers". Upon investigating, the chain marks were not aligned with the gears. So I thought I did something wrong, so took the timing chain system apart and started over.

I made sure everything was aligned and that the chain was on the outside of the two casting bosses.

Rotated the crank clockwise by hand and paid attention to what was happening. I saw that the chain was not tight all the time when rotating (the chain between the intake gear and the crankshaft gear). It looked like when the cam lobes were ramping off of the valves, the intake cam would "lurch" a couple of degrees clockwise (when I was rotating the crankshaft slowly clockwise), causing the timing chain to go slack (between the intake cam gear and crankshaft gear). After a couple of crankshaft rotations, the chain marks were no longer aligned (they were off 4+ teeth, not a small amount)

So I thought I maybe had a very weak chain tensioner, so I purchased a new one (the latest GM design with the retaining clip).

So took the timing chain system apart and then proceeded to put it back together. Again aligning all gears to the chain marks, the cam sprockets were engaged into the grooves, compressed the timing chain tensioner, made sure the chain was to the outside of the two casting bosses and then released the timing chain tensioner. Everything looked tight

I had someone else rotate the crank clockwise and paid close attention....and found the same thing happening (that is, the chain would periodically go slack between the intake gear and the crankshaft gear while turning the crankshaft clockwise by hand). Again, after 4 or so revolutions of the crankshaft, the timing chain was now off 4 or 5 teeth

I cannot see what I am doing wrong.

The only thing I could thing of was that I did not use new gears during the rebuild. I would not of expected the gears to wear that much and visual inspection of the gears did not show anything unusual.

Any thoughts on what is causing this?

Note: I do not think any of the valves were hitting when the chain jumped, as there was no unusual force required to rotated the crank

Henry3959

Your not doing anything wrong. Once you start rotating the assembly, the marks go out of sync. If you could rotate it backwards it would re-sync. The marks on the chain are only good for assembly.... nothing else.

Sharkey

iTrader: (1)

exactly, the chains dont line back up with the colored links after you turn it. the way to know if its jumped or not is to rotate it a few times, then you can count how many links each cam and the crank is "out", it will be the same number on all 3.

exninja

iTrader: (1)

It takes like 40 rotations for the marks to line up again.

Medida

Interesting, I did not know that (that after rotation, the colored links no longer align with the cams). I did not count the number of teeth that were no longer aligned between the gears and the chain.....but remember that they were all similar

Should I be concerned about the "slack" that is occurring between the intake cam gear and the crankshaft gear? Again, it looks like the camshaft is advancing faster in rotation than my rotating of the crankshaft when the cam lobes are ramping down in the valves.

I am rotating this very slowly (since cams were not degreed in yet, I was rotating slowly to make sure the valves where not hitting)....so it is not a situations that the engine would ever see (even during starting, as the engine speed will be 10x plus faster than I am rotating)

jdbaugh1

iTrader: (1)

It is normal to have some slack in-between the exhaust and intake cam at certain degrees of rotation while cranking the engine slow during installation. The tensioner isn't really taking up the slack at this time.

07blackg5

iTrader: (8)

Oil pressure will tension the chain when it is running.

Medida

To All
appreciate your quick responses. Thanks!

mrbelvedere

iTrader: (3)

you should check the piston to valve clearance and do it without the head gasket

Henry3959

I have been looking for that spec myself and cannot find it

Sharkey

iTrader: (1)

why would you do it without the head gasket?

Henry3959

Unless you know exactly what your compressed head gasket value is. Personally, I don't like re-crushing MLS gaskets

mrbelvedere

iTrader: (3)

so you don't ruin a new gasket an
d an old gasket can be warped and give you a wrong measurement that's why you clean and measure the compressed gasket in 1 section and add that to your clearance for your total piston to valve clearance

lsj gasket is .027 compressed

lnf gasket is .035 compressed

le5 I believe is .025 compressed

standard clearance for a stick car Is .095 intake .105 exhaust the reason you run more room on the exhaust is the valve opens as the piston is coming up the reason you run more room on a stick car is crank flex from a missed shift

auto cars you can run closer piston to valve clearance ive seen people run them into the .070 to .080 intake and .090 exhaust

Sharkey

iTrader: (1)

that makes sense. ive always done it with a head gasket, however most of the stuff ive built is race stuff using copper gaskets.

mrbelvedere

iTrader: (3)

werd up dawg