Masterspykiller

SOLVED - REPLACED TIMING SPROCKET WITH EXACT DUPLICATE AND PROBLEM SUBSTANTIALLY ALLEVIATED!!

Building a new engine using same block as ZZ4 crate motor (casting #10243880, 2 bolt mains, one piece rear seal, normal cooling, etc. ). This block uses a bolt on retaining plate to keep the cam from walking forward into the timing cover.

The block was professionally machined (.030 over, line bored, etc.) by a well known Corvette engine builder who also installed the bottom end and the cam with retaining plate.

When I bolted on the new timing sprocket just finger tight (all 3 bolts), it pulls the cam to the front of the motor (as expected) and the cam lobes look well aligned with the lifter rollers. That's all good as far as I can tell.

When I rotate the timing sprocket by hand it moves smoothly about 300 degrees of rotation, but GRINDS ON THE RETAINING PLATE HARD for about 60 degrees before it spins easily again. It grinds on the same spot of the timing sprocket/retaining plate every rotation. The friction is so significant, I can barely turn the cam past this area using my pretty strong hand on the timing sprocket. I know this will get a little worse when I torque down the cam bolts too. THIS HAS ME WORRIED AND PUZZLED.

If the retaining plate, cam face, and the timing sprocket were perfectly flat and parallel, they would either touch all 360 degrees or not touch at all 360 degrees. Right?

Therefore, SOMETHING is NOT flat or parallel, but what?

If the timing sprocket and/or cam face were NOT parallel to the retaining plate, the SAME part of the timing sprocket would grind all 360 degrees of rotation. Right?

If the retaining plate bulged out a bit, the ENTIRE timing sprocket would constantly rub that spot of the retaining plate all 360 degrees of rotation. Right?

If the cam were not perfectly straight, one part of the timing sprocket would constantly grind against the retaining plate all 360 degrees of rotation. Right?

SO, HOW DO I GET ABOUT 300 DEGREES OF NO FRICTION ROTATION, AND ABOUT 60 DEGREES OF VERY HARD FRICTION and, how do I fix the SOURCE of the problem?

I do realize one could machine the retaining plate face or the back of the timing sprocket to an angle to minimize or eliminate the grind, but that seems very imprecise and just "masks" the real problem. Besides, I don't have access to a machine shop.

Inserting shims between the face of the cam and the back of the timing sprocket to move sprocket away from retaining plate WILL NOT WORK, it just pushes the cam to the back of the engine and the lobes mis-align with the roller lifters.

Any suggestions welcomed! My engine build is dead in the water until I figure out this conundrum.

Cheers and Thank you In Advance for your ideas!
M

DanielRicany

Are you sure you didn't bolt the sprocket on backwards?

Masterspykiller

UPDATE: I TRIED TO REVERSE SPROCKET, BUT IT WILL NOT BOLT ON THAT WAY. THE SPROCKET CAN ONLY BE MOUNTED ONE WAY, WHICH IS SMOOTH SIDE TO BLOCK, SO THIS IS NOT THE PROBLEM.

Well, it would not be the first time I did something silly (i.e., carbon based error).

The timing sprocket has a machined smooth, flat side with a few oil grooves, the other side is raw cast metal with a very rough texture. I put the smooth, flat side toward the block.

I think that is correct, but let me know if I got it wrong.

Thanks! M

DanielRicany

Couldn't tell you without seeing it. Flip it around and just see if it still does it. Then report back.

cgantner5150

Is the chain on? If not a lobe could be rubbing a rod? I did that on my 385 and it stopped the cam completely. Scared me for a second.

Masterspykiller

Good thought! I have not installed the rods yet and the lifters are very smooth in their bores, so I am pretty sure that is not the issue. Also, I can see scratching on one area of the retaining plate where the timing sprocket is grinding and audio cues indicate grinding sound from the sprocket/retaining plate. If I loosen the cam bolts a little (so the timing sprocket moves away from the block a little), I can spin the cam quite easily 360 with no friction.

This one has me stumped good!
M

DanielRicany

What type of gear set is this?

DanielRicany

Can you put the distributor in place and try it?

Masterspykiller

Cloyes Race True Roller 9-3145-5 (since bore has been honed, must use set that is -.050 shorter)= 3 keyway options

Masterspykiller

I have not installed the intake base or other parts yet. I haven't even looked to see if the old distributor is in acceptable condition yet (I'm pretty sure I'll replace the cap, rotor, etc., but not sure what else).

I have not attached the new cam gear to the distributor either.

Some of the OLDER L98 engines did not have the cam retaining plate, so your idea of installing the distributor in THOSE engines is solid because it might move the cam forward enough to maybe clear the friction area.

Tomorrow, I could do that and try to hold the distributor in place, but the cam retaining plate will NOT let the cam move forward in this engine at all. Not even .010 more.

I'll try it anyway, just because I have no idea why this is rubbing and trying something is better than nothing!

Thanks,
M

DanielRicany

Well I was thinking of the cam moving backwards forcing the sprocket to hit.

DanielRicany

I would try to use a timing gear set confirmed to work with the ZZ4 short block. I'm sure some of the members here know which ones work for certain. That's were I would start so I know I'm not chasing my tail.

mtwoolford

When I rebuilt a ford 460 I ignored the warning not to mess with the cam bearings; evidently they can shift around a bit; long story short, I had to relieve each bearing slightly before that cam would rotate smoothly; apparently not unusual on those blocks; I think either a bearing was installed a bit askew or your cam is not perfectly straight.

you can pull the cam, put it bewtween two vee blocks and rotate it slowly and for radial run out...i.e a ever so slight bend

mtwoolford

long story short, take off the retaining plate and see if the cam rotates freely / smoothly

Masterspykiller

Thanks for the suggestion! Logically, a very slightly bent cam could create the problem I am having.

I will check that tomorrow, being very careful not to mess up the cam bearings as I remove/reinsert it.

I'll post results tomorrow evening.

Thank you all for your time and mental energy.

Cheers,
M

Masterspykiller

Ok, I did everything that was suggested, but nothing appeared abnormal to my eye.

So, for giggles, I ordered an EXACT duplicate of the timing gear set and installed the cam shaft sprocket. IT DOES NOT RUB ANYWHERE NEAR AS MUCH as the other sprocket, but it does rub a tiny bit.

All I can surmise is that the original sprocket has an imperceptible bulge on it somewhere. The new sprocket does not rotate entirely smoothly: I can feel a little "rub" between 9 and 11 o'clock positions, but it is not terrible. So, there might be a slight bulge in the cam retaining plate or the block at that position.

In any case, it seems that the problem has lessened to the extent I am willing to continue the build. I am pretty sure the little rub will smooth itself out shortly.

THANK YOU ONE AND ALL FOR YOUR THOUGHTS!

Cheers,
M