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Discussion Starter · #1 ·
the other day i was turning my engine over when i heard a big "clunk", i checked everything out and found that my timing chain had broken, so i bought a new chan and installed it today, when i was adjusting the valves by hand i noticed that only the #1 cylinder pushrods were moving, i was thinking what the hell , did i d0 something wrong?? it crossed my mind that my cam might of broken, buti thought theres no way in heck soemthing that strong could break, well i was wrong, i pulled the cam and itcame out in three separate pieces!!!! the cam is a new comp extreme 286 solid roller, the engine is almost brand new, i took it to the track a few weeks ago and ran a 12.4 with it, now what would cause the cam to break??, i remember when i installed it, one of the bearings was tight, but i thought after hitting 7000 rpm a couple times, it would of worn down alittle, could the cam of ceased in the engne because of the tight bearing?? should i pull the whole engine and check everything out?? or just put a new cam in and go happily on my way, do u guys think i need new cam bearings installed? maybe it was a poor quality cam? i dont know, im really stumped,any help would be apreciated i just hope comp will give me a refund on this camshaft, cause it sure was expensive.
Preston
1967 Chevelle 12.49 @ 111
1999 Ford Lightning 13.9 @ 98 w/ fuel delivery problem!!!
 

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Wow, now that is the start of a real bad day. I would call Comp cams and discuss this with them. I would expect them to replace the cam.

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Redrum (or Mike)
68 Corvette - 383 CI 427 HP
69 SS Chevelle being updated to Pro-Touring
97 Z-28
 

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First of all, what do the bearing journals on the cam look like? Do any of them show signs of scoring?

Next, do you have an old cam with good bearing journals that you can just stick in to check how it turns in the bearings?

Last, yes, if there is a problem there, you definitely need to pull the engine. Cam bearings can't be installed without pulling the engine.
SORRY!

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Tom Parsons
 
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Did you have the spring installed height and spring seat and open pressures properly set up by a machine shop to Comp Cams specs??? Too high spring pressure can break the cam as it's a cast core, not a billet.

The tech's at Comp informed my machinist of this fact and emphasized the fact that the spring pressures were critical to long cam life. I believe the seat pressure spec was 170 lbs at 1.900 or 1.950", and something like 440 lbs at 1.250...call Comp to be sure as I'm not 100% on those numbers.

I'd pull the motor and check for any foreign debris, and have new cam bearings installed.

Also, did you check for proper piston to valve and retainer to valve seal clearance? again...very critical.

BTW, is this for a bbc or sbc? just curious as that's the same cam I run in my 414 ci bbc..XR286R-10.

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Malibumotorsports
79 Malibu, 414 ci BBC, 3550 lbs.
10.92 @ 122 mph, 1.55 60'
BSE Power
 

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Discussion Starter · #5 ·
the journals look fine, no wear at all, ill try putting in a cam and turning it , to see what happens.
thanks
Preston
 

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Discussion Starter · #6 ·
the cam is in a 406 sbc, no i didnt know that piston to valve clearance and retainer to seal clearance were so critical,i chevked piston to valve but didnt check retainer to seal.how would i check retainer to seal clarance? my springs are the recommended pressures. thanks alot
Preston
 
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BTW, the specs I listed were for the bbc spring, so the sbc may differ.

The easiest way to measure retainer to seal/guide clearance is to remove one spring and re-install the retainer/keepers. Now holding the retainer with your fingers (to keep from dropping the valve in the cylinder), rotate the engine till the valve peaks it's lift...now use a dial caliper to measure the clearance between the bottom of the retainer and the top of the seal/valve guide.

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Malibumotorsports
79 Malibu, 414 ci BBC, 3550 lbs.
10.92 @ 122 mph, 1.55 60'
BSE Power
 

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Preston,
First of all, if the timing chain actually broke while the motor was running, I can almost guarantee you that it bent some valves, so you might as well figure on pulling the heads for a look.
Second, if one of the cam bearings was tight when you installed the cam...you should have stopped right there and found out why. Even though you say the cam bearings "look" ok, if one was tight it puts a tremendous amount of stress on the cam.
I doubt that there was a defect in the cam...if there was it would have broken a lot sooner. I am betting that the broken timing chain and the broken cam are somehow related. I dont know what motor you are running, but if the chain broke at just the right spot, it is possible that one or more of the connecting rods came around and hit the camshaft and broke it. I bet if you look very closely at the cam, you will find more damage.
By the way...just my opinion but I would be pulling the motor and disassembling it to find all the little pieces of camshaft that I bet are floating around.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100
 
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Good advice Bill. I wasn't really paying attention to the broken timing chain, but there does appear to be a chain of events that happened with this failure.

It certainy is best to pull the engine completely down and clean everything completely. Also take great care to inspect everything for damage...as Bill said, bent valves, contact marks on the piston domes, check pushords for straightness, check the roller lifters for rough feeling bearings in the rollers, etc, etc. Upon reassembly, check every dimension and record it, and pay attention to every little detail...if unsure about any little detail, ask your machinist, or here. I'd hate to see the same problem occur twice.

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Malibumotorsports
79 Malibu, 414 ci BBC, 3550 lbs.
10.92 @ 122 mph, 1.55 60'
BSE Power
 

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Discussion Starter · #10 ·
thanks for all the info Bill and Todd. when i installed my camshaft and noticed it was tight in the bearing, i immediatley went and asked my machinist, he said it would be alright if i could turn it by hand, which i could. i did bend a pushrod, so i immediatley pulled my heads today and found little marks on the vavles and pistons but nothing serious, so i lucked out there, i liked ur idea bill , about the rods hitting the cam and breaking it, because i did have to grind down the rods since theyre 5.7 in a 400 engine for cam clearance, so thats probably what happened, i have decided to pull the whole thing and check it out, thanks for all the info guys.
 

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Preston..First off that is a huge bummer..

I know you just recently got it running..

I'm very curious as to what caused the failure to start with?
What rate springs were you running?. One thought is.. Did you clearance all of the rods? or just the few that were close to the cam lobes with the chain installed? I had my machinist clearance all of the rods just in case of a chain failure.Once your chain broke I'd bet that some of the unclearanced rods made contact with the cam. That may be why its broke into three pieces. Let us know what you come up with..

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You can sleep in your car,but you cant drive your house.
Tony. H . 406 powered , Mohave Gold , 72'Malibu
 

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Discussion Starter · #12 ·
ya Tony, i think thats what happened, i only clearanced the three rods that hit the cams lobes, when the chain broke it screwed up the timing and took out the cam, im guessing two rods hit it, im only hoping that my rods are ok, thanks alot
Preston
1967 Chevelle [email protected] 111 mph
1999 Ford Lightning [email protected] 98
 
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