Whilst installing a set of custom cams for my turbo engine and during the break-in period my dumbass somehow managed to bend 4 intake valves. This is my story thus far. I'm just looking for any insight you guys could give me. I'm not quite sure why the T-belt jumped, but it may have something to do with the fact that the cams have around 12mm of lift on top of the Crower valve-train.

7/14/02

I successfuly broke in the cams and got the engine timed correctly. After the prerequesite 15 minute at 2000 RPM break in period. I re-checked the engine bay, for leaks, ticks, oddities, ect... All seemed well. The engine sounded good, idled stock, no lope at all.

So I took the car out for a test drive. I got no more than a mile before the car cut off on me, just after I clutched in to stop. I stopped and tried to re-start it and I heard a horrible noise from the engine bay. Up comes the hood, my worst fear was that I had snapped a timing belt. Fortunately that wasn't it. I didn't see any puddles under the engine either. So I onced over the engine bay checking for anything out of place, and there is was. My cams were out of time, by about 5 teeth. Oh no........

After a short tow back to the house. The spark plugs come out, no damage to the plugs. Thats a good sign. The valve cover comes off, not oddities in the valvetrain. Not a keeper, sping or retainer out of place. Cams apprear un-damaged. The belt is reset and timing checked again. A compression test yields 205,205,205,210.... intesrestingly high for a stock block LS. Though it's prolly due do the increased profile of the cams. So I'm lucky, It appears there is no damage to the engine.

However after a 2nd test drive, only 2 mile farther away the same thing happens, timing jumps again!

Appearently, either my timing belt is streched, my tensioner is weak, or both. I have a feeling with the stock cams/springs the belt was tolerent enough not jump time. However with the increased straign from the springs/cams it just doesn't want to stay seated. So i'm off to get a new timing belt and possibly a new tensioner pulley/spring. I can get the belt tonight, and manually pull the tension spring to force the slack out of te belt. The pulley will have to be ordered. With a new belt I can polly make do until the tensioner gets here tomorrow.

7/15/02

Again with the bad news however. The 2nd time the belt jumped I wasn't so lucky. 150,0,150,0 on the compression tester. So what does this mean? Most likely a lunched set of valves, and possible piston/sleeve damage. So at 10:00 pm when I return home, my best friend and I comence to tearing the engine down. We successfully remove the head with the block still in the chassis by 11:15 pm.

A close inspection of the head reveals that the #2 & 4 intake valves are bent from a slight impact with the piston. No damage to the block itself luckily. So at this point we call it quits for the night after some extra tinkering. The next day, we call around to a few friends to see if any one has an LS head. I got lucky again and was ablt to trade a CTR flywheel(14lbs) I had lying around for a spare LS head.

After an extensive cleaning job on the head and all it's components, we thought to check the old head to see if the valve guides were damages in the incident. No they weren't. While we had everything apart we figured that we may as well port match EVERYTHING we can get our hands on. From skunk2 intake manifold, to the exhaust housing on the turbo had been port matched. I've been wanting to do it, but couldn't justify pulling the entire front for my car apart to do it......damn turbo hybrid. I think I wore out my die grinder

So we'll double check the valves and what-not tomorrow. Just for safe keeping and start re-assmebling the top on the engine. Hopefully by tuesday or wendsday it'll be ready for a real test drive. Wish me luck.




[Modified by Speed PHreak, 2:47 PM 7/16/2002]

 

It may be informative to Clay your engine's piston/valve clearances. I believe this is a difficult diagnosis method though . . .

Another way to find out how much clearance there is with your block/crank/rod/piston/headgasket/head/valve/rocker/cam/cam timing setup; is to share these specs so that we can calculate the valve/piston clearances.
Knowing each of these parts, will allow clearances to be ascertained with some reasearch. Then you may not have to clay your engine.


Good Luck.

 

What specs can I get for you?

I hoping that it was just the T-belt, i've had it off and on I dunno how many times(maybe 7~8 times) and it had about 30K miles on it. I know you're suppose to replace it everytime you take it off too, on me I guess.

 

I'm not sure the problem is with your timing belt although you should probably replace it with a new one. If you put a high lift Crower cam with stock pistons, you might be hitting the valves into the pistons FIRST and that act causes the belt to jump. You need to use clay to check your piston to valve clearance. Use a used head gasket on the motor when you do this check. Second, did you replace your valve springs with the new cam? You may be getting coil bind with the stock springs (because of the higher lift of the Crower). Also the springs may be just to weak to work with the cam. Reading your post it sounds like you are not a rookie at this. Just remember, you can't just change one component without thinking about everything else that the change will affect. Let us know...

 

Earl:

I'm with you about the clearences between the piston and valves. I'm not running higher compression pistons, and the first time my belt jumped like 5 teeth on a cam without any valve damage. The next time it jumped more than that so I'm fairly sure that i'd good on that aspect. The new timing belt was a much snugger fit than the old one, so i'm thinking that was some of the problem, the tensioner may also be partly to blame for not taking all the slack out, due to a weakened spring.

I am running Crower dual valve spings and retainers. With the amount of lift that these cams have, it's a must. These cams are custom from Web Cam, a little less than 12mm of lift, but with a low duration profile more suited to boost. I've been researching some and have found that the DOHC VTEC guys have trouble with some of the aftermarket cams jumping time. They also have to run higher seat pressure valve springs. That may be my problem also. Most wind up running a Power Extreme timing belt. The old t-belt coupled with a weak tensioner spring, could have been my engine's kryptonite.

Thoughts?

 

bump

 

Sounds good. We run Web cams and springs with no problems. Gone 9.40 @ 156 with a well used stock timing belt and tensioner.
The real question is are they stock pistons or aftermarket pistons? Stocks don't have the valve clearance built into them as an aftermarket would have.

 

Stock pistons, you think i'm gonna run into problems?

I really like Web, they were great all around. I just wish I had a chance to test out their product before my engine got fubar'd


[Modified by Speed PHreak, 7:45 PM 7/16/2002]

 

Web's the best. Very well could be a clearance problem as the valve reliefs are not as deep as aftermarket.