Figuring out if a cam is twisted
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From: Waco, TX
Figuring out if a cam is twisted I need to figure out if one of my cams was "twisted" by the damage caused by faulty CompCams cam gear. The cam slid right out of the motor and looks to be in perfect shape. Looks brand new (it was, it only had 2 hours of run time before the brand new cam gear let go). The broken cam gear was the only damage found in the motor (aside from a ton of bent valves). This is an LT1, btw. The cam is a Thunder / CompCams XE 230/236-112.
I'm thinking that I can put the cam in a block and use a degree wheel, determine the IVO/IVC of the #1 cylinder, and then walk the degree wheel through the firing order (1-8-4-3-6-5-7-2). If the #8 IVO/IVC event is not 45 degrees off from #1, then the cam got twisted. Right?
I would "assume" that since the spark events are 45 degrees apart (360/8), the cam events should be also. If it proves to be easy enough, I might do all of the timing events. I do have a complete degree wheel setup.
(oh, and no more CompCams timing setups for me
)
I'm thinking that I can put the cam in a block and use a degree wheel, determine the IVO/IVC of the #1 cylinder, and then walk the degree wheel through the firing order (1-8-4-3-6-5-7-2). If the #8 IVO/IVC event is not 45 degrees off from #1, then the cam got twisted. Right?
I would "assume" that since the spark events are 45 degrees apart (360/8), the cam events should be also. If it proves to be easy enough, I might do all of the timing events. I do have a complete degree wheel setup.(oh, and no more CompCams timing setups for me
) 
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From: K-W, Ontario
I have never seen a cam gear break apart like that!
At the risk of insulting you, I have to ask...did you set the valves properly?
I'm thinking the pre-load was set way too tight and there was definite PTV
contact.
If the cam walked out, I'd say swap the cam for peace of mind.
I would also pull the heads and check the lifters and piston crowns.
Twisting the cam would be tough to swallow. I would think the lobes would
rub down before the core warps.
At the risk of insulting you, I have to ask...did you set the valves properly?
I'm thinking the pre-load was set way too tight and there was definite PTV
contact.
If the cam walked out, I'd say swap the cam for peace of mind.
I would also pull the heads and check the lifters and piston crowns.
Twisting the cam would be tough to swallow. I would think the lobes would
rub down before the core warps.
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From: Waco, TX
I used the same procedure I always use on setting the valves. 3/8 turn past zero lash, using this procedure:
http://www.akmcables.com/valvelash101.txt
(I can never remember, so I print that out and take it with me... every time
). I'm getting a different/new shortblock. Was hoping to reuse this cam in it. The motor ran fine for ~2 hours (I did a cam swap & new timing gear install, got everything buttoned up, let it run for a while, drove it around & drove it to work, I was driving home one day, getting on it a little, when it suddenly stopped running - I didn't even hear any noise!).
I did this 2 years ago, so memory's fuzzy... lifters looked fine. The cam plate didn't show any real wear on it either, so I don't think the cam walked. There was nothing seized up in the motor. Just a busted cam gear. The valves were bent, the pistons didn't get any serious eyelets though (since the LT1 pistons aren't flat tops like the LS1 - they have valve reliefs). I wasn't going to reuse the stock shortblock anyway.
The lobes on the cam looked perfect...
http://www.akmcables.com/valvelash101.txt
(I can never remember, so I print that out and take it with me... every time
). I'm getting a different/new shortblock. Was hoping to reuse this cam in it. The motor ran fine for ~2 hours (I did a cam swap & new timing gear install, got everything buttoned up, let it run for a while, drove it around & drove it to work, I was driving home one day, getting on it a little, when it suddenly stopped running - I didn't even hear any noise!).I did this 2 years ago, so memory's fuzzy... lifters looked fine. The cam plate didn't show any real wear on it either, so I don't think the cam walked. There was nothing seized up in the motor. Just a busted cam gear. The valves were bent, the pistons didn't get any serious eyelets though (since the LT1 pistons aren't flat tops like the LS1 - they have valve reliefs). I wasn't going to reuse the stock shortblock anyway.
The lobes on the cam looked perfect...
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From: K-W, Ontario
turn the engine 90 degrees clockwise, so the timing pointer is at 3:00
check all 16 if you're ****.
what he's doing and probably is the cause of your mishap.
His method can't ensure that the lifter is on the baseline of the lobe. That's
where the lifter NEEDS to be when setting pre-load. Anything else and you're
sure to reduce performance, or possibly cause damage.
Yes, each valve must be checked. Being **** ensures perfection; "eyeballing",
or estimating the "3:00 position" is just a bad scene.
My favourite line is:
Use a wrench to add 1/2, 3/4, 1, or however many turns you want. MHO: anywhere from 1/2 to 1 turn gives the exact same result.
THat procedure seriously needs to be taken down.
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From: Waco, TX
While I appreciate your feedback, I don't think the procedure caused my problems. The car ran GREAT for two hours of run time. No problems at all idling or running. Then boom. It quit. I've worked on cars with mis-adjusted valvetrains, and there was something "not right" about them. This one... there wasn't. Hydraulic lifter / rocker arm adjustment at this car's level (street car, NOT race car) isn't rocket science. That's one of the benefits of it.
Back to my question. Will the assumption of a 45 degree offset in firing order work to enable me to determine IVO times between the 1st and 8th cylinders - and would any differential indicate that the cam was indeed twisted?
Back to my question. Will the assumption of a 45 degree offset in firing order work to enable me to determine IVO times between the 1st and 8th cylinders - and would any differential indicate that the cam was indeed twisted?
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From: Upstate NY
Originally Posted by Camaroholic
Back to my question. Will the assumption of a 45 degree offset in firing order work to enable me to determine IVO times between the 1st and 8th cylinders - and would any differential indicate that the cam was indeed twisted?
FWIW, engine fires every 90 crank degrees and every 45 cam degrees. So wouldn't cyl 8's lobes be 45 deg + 90 deg (bank angle between 1 and 8) = 135 deg after cyl #1?
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I don't see how the cam could be "twisted", the rest of the valvetrain, pushrods,valves etc will give before the cam is tweaked torsionally. I would put it on some v-blocks and check the runout with a dial indicator.
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From: Waco, TX
Yeah, the valves were definitely the components that "gave" in this instance. Some of them simply tucked up a little under the seat, the rest were undamaged. None of the valves were dropped or had super gnarly bends in them though. I did not roll the pushrods on glass, but they all "seemed" straight - they were Trick Flow hardened units with manley guideplates, pushing Comp HiTech Stainless rocker arms.
I'll try both the degree wheel and the V-blocks for runout. Good idea. Thanks.
I'll try both the degree wheel and the V-blocks for runout. Good idea. Thanks.
