I'm driving myself nuts...About a month ago I had the joy of breaking an exhaust rocker, which in turn hit the retainer to the point that the keepers jumped out and boom bent valve. During the carnage, the jesel belt drive had jumped a tooth and tagged all the remaining exhaust valves. At least I assume this was the course of events. Luckily the bottom end didn't need to come apart, just had to pretty up the wrecked cylinder piston a touch, exhaust valves, and a guide in the head.

I had the cam installed at 110 and during disassembly i checked cam timing at 126 degrees. Counting the top pulley there are 54 teeth, which in turn nets 13.3 degrees per tooth, hence i determined it had jumped a tooth due the 16 degrees of retard from installed. I verified that the jesel top pulley had not moved from when installed, 4 degrees advance on the pulley marks. So i figure maybe the belt stretched during the wreck the remaining 2.7 degrees...wishfully thinking.

Got the new belt and tossed it on and degree the cam in. To get to 110 i need to advance it nearly the 3 additional degrees i saw from above. I've put 3 belts on this combo and have never had to adjust the jesel top pulley. So i do what any of us would do and check to my math a few hundred times, degree it in on cylinder 1 and cylinder 6 1000000000 times (0.5 degree difference between the cylinders, 0.5 less on 6), and had someone else degree it in to make sure i'm not just an idiot. I never throw anything away so i grab some of my old belts. All have to be advanced 3 additional degrees to obtain the desired 110, when previously that was never a required. Borrowed another degree wheel and another dial indicator, same results.

Pulled the balancer...cam lower drive pulley key is not sheared, cam key is also fine. Checked p to v installed at 110 and i have identical clearances as prior to the wreckage on cylinder 1. I plan on checking p to v on 6 also to verify that it follows cyl 1.

Some background...this is a 565 baby blower combo with 300-310 on the seat. Cam core is black so i assume it's 5150 or 5160 (comp originally)

Is there anything else i'm not thinking of??? besides the cam has twisted?

how was top dead verified after re install

.050 before .050 after, centered on wrist pin centerline, no indicator change rocking piston up and down. Adjust pointer until same degree measurement

This message has been edited. Last edited by: I Hate Dragsters,

quote:

Originally posted by I Hate Dragsters:
Cam core is black

wouldn't run that core in any race engine, they have a history of breaking.

quote:

Originally posted by 1320racer:

quote:

Originally posted by I Hate Dragsters:
Cam core is black

wouldn't run that core in any race engine, they have a history of breaking.

Another reason I'm skeptical of the situation.

Turn the camshaft around and stick it in backwards, see how it goes in.

If cam timing checked out on 1 and 6, obviously you're thinking it's bent (twisted) behind the front journal.

How do ya know for certain it wasn't just installed previously, 3 degree's retarded from where you intended?

I've degreed this cam in probably 5 times since it was originally built. A few times to install new belts and twice on freshen up. Every time I've checked to verify that it was installed where intended, 110 degrees. I'm overally anal and i'll check it at .050, .040, .025, ect. evertime i assemble or put on a new belt. I also make another person verify that they get the same numbers that i do. Not once have I had to adjust the Jesel pulley. Dead nuts to 110 every time.

The most recent assembly I took the time to check cam events in addition to degreeing the cam. Everything was spot on to the cam card, both intake and exhaust, no adjustment required of the Jesel pulley. I verified on several cylinders.

Piston to valve clearances when i degree to 110 are identical as the previous assembly, with the exception that I have to advance the Jesel top pulley another 3 degrees to obtain 110 degrees installed.

quote:

Originally posted by I Hate Dragsters:
I've degreed this cam in probably 5 times since it was originally built. A few times to install new belts and twice on freshen up. Every time I've checked to verify that it was installed where intended, 110 degrees. I'm overally anal and i'll check it at .050, .040, .025, ect. evertime i assemble or put on a new belt. I also make another person verify that they get the same numbers that i do. Not once have I had to adjust the Jesel pulley. Dead nuts to 110 every time.

The most recent assembly I took the time to check cam events in addition to degreeing the cam. Everything was spot on to the cam card, both intake and exhaust, no adjustment required of the Jesel pulley. I verified on several cylinders.

Piston to valve clearances when i degree to 110 are identical as the previous assembly, with the exception that I have to advance the Jesel top pulley another 3 degrees to obtain 110 degrees installed.

Well then you know for certain the cam is bent.

Slide it in backwards.

so it is bent and slides in cam tunnel.... i ain,t buying lol

Put it in a lathe and run a dial indicator on the journals

If it was bent it wouldn't turn easily in the cam bearings without the belt connected

Bent and twisted are 2 different things

The belt would break before the cam twisted is my thought..

I had a racer next to me a couple years ago that broke the pin on his cam....They were able to fix it and no other engine damage....It did have a Jesel

I've never seen that one before !!!

i don't think it's bent...twisted possible. I'm going to pull the cam adapter off and see it might have been unfriendly to the cam pin.

The pin is something to look at and sounds like a good idea. Still if it's a black core I would be scared to use it.

It's not twisted, if it were twisted it would be bent.

I'll say again, if 1 and 6 checked out the same cam timing, you're then talking about it being twisted behind the front journal, it's not though, it's a pin problem.

If it were twisted behind the front journal hypothetically speaking, I bet you couldn't turn it around and stick it in backwards and have it go in very far, because it would be bent, it's not though, if anything it's the pin.

But try it, turn it around and stick it in backwards. The chances of it twisting and not being bent are low.

5160 cam cores are brittle, that's why they break in two, they won't do well with twist. If you need one good with twisting, get a 9310 core.

unfortunately i can't pull the cam out with it in the car...shield is in the way and there's plenty of electrical junk attached to the shield, so i'm yanking the engine.

For what it's worth the cam spins free. The pin is square to the face of the nose of the cam using a vee block as a square.

Updates to follow...I'm sure you all can predict what i'm going to do.

quote:

Originally posted by I Hate Dragsters:
unfortunately i can't pull the cam out with it in the car...shield is in the way and there's plenty of electrical junk attached to the shield, so i'm yanking the engine.

For what it's worth the cam spins free. The pin is square to the face of the nose of the cam using a vee block as a square.

Updates to follow...I'm sure you all can predict what i'm going to do.

Cwank?

checked tdc on cylinder 1 and 6. Pointer is spot on.

quote:

Originally posted by I Hate Dragsters:
checked tdc on cylinder 1 and 6. Pointer is spot on.

you're gonna pull the cam and check it for bent, if it'll slide out the back.

If it won't, you're gonna order a new camshaft tomorrow?

There's a local engine builder with a cam doctor...going to have them measure it and go from there.

That'll work. What are the specifications? Brand?

Do you know for certain which core it is?

9310, 8620, 5160, 5150?

I have seen camshafts break but not twist. Not saying it could not happen but seems to me it would snap and break in two before it would twist much at all.

I would call Bullet cams and ask them. They are really good and have stuff check every lobe. They should be able to tell you is many cams twist.