I built this motor last year. It now has 9000 km on it and over the last few days ive beed noticing a vibration in the motor. So I did a compression test and I have 140 psi on all cylinders except for #8 which has 0 psi. Then I pulled the valve cover to find that the intake valve on #8 barely moved when I bumped the motor over. Is the loss of compression because theres no air getting in to be compressed or could it be the rings? Also why all of a sudden would this happen?

Engine specs:
4 bolt 350 0.030
xe268
vortec heads
performer intake
flatop pistons
Any input is greatly appreciated

 

There's a thread about compcams camshafts failures..
Seems quality control is poor regarding their camshafts.

Did you install the cam yourself?

https://www.thirdgen.org/techbb2/sho...hreadid=251612

 

Yes, I installed the cam myself, followed all directions to the tee. I just find it odd that this would happen after so long. Anybody have any info on the compression thing?

 

Because there is no air getting in. There is nothing getting in to be compressed

 

Yeah thats what I was thinking or at least hoping.

 

What valve springs did you use? What installed height? Did you get the valve guides machined down?That cam is right on the ragged edge of smashing the retainers into the top of the guides, in stock configuration. That will result in certain and unavoidable catastrophe.

 

I agree with RB. On unmodified Vortec heads, there is a real slim line there. I measured mine and they would BARELY fit, but leaving no room for that "added clearance."

In the stock form, they aren't performance pieces. They have very limited clearance between, as RB said, the top of the guide boss and the bottom of the retainer.

My bet is on you ran out of room there.

 

Along with the head clearences, did you use the Comp. break in lube, the red stuff? I wouldn't let that get anywhere near my cam, its like water, I used the thick gray Crane moly break in lube with my XS268 cam and never had a problem even after a horrendous break in.

 

I lost two xe294`s in mine before I went to a old comp cam design..no problems after that..I think the ramps on the XE line are too aggresive for the diameter of the chevy lifter. I build many street strip engines and have problems with almost all chevys. Now I have built many small block fords and BB chryslers using the XE line and
have never lost a lobe yet. I lost the lower end of my 454 due to all the metal loss from the cams, I went to a solid roller, at least it has a better chance of not losing a lobe. Obviously break in was not the problem, if the lifters were not spinning on the cam it would have been toast in minutes, poor metal heat treat would be my guess.

 

O.K heres the specs my head builder gave on the receipt.
Retainer to seal .560
Max valve lift .500
CB at 1.165
Spring preasure 110 @1.700, 310 @ 1.200
I also had these heads machined to fit dampners.
And yes I did use the red lube. Can you guys recomend another cam or should I stick with the xe268.

 

What valve springs are these?

I've used the red stuff on my LG4 in my Caprice when I put in my Xe256. Engine runs fine, has been for several hundred miles now.

 

Installed height minus coil bind height minus safety margin = max lift

1.700" - 1.165" - .060" = .475"

That's the max valve lift you can run without risk of coil bind under dynamic conditions, assuming perfect installed height. If the installed height is any less than stock, even a few thousandths, you're into wipe-out territory.

There's your problem right there.

You need better springs.

The XE268 itself is fine; the problems that most people have with them, are caused about 90% of the time by either retainer-to-guide interference, or inadquate valve springs. You just have to be REAL CAREFUL how you set up your heads, or better yet, use 1.45" springs. Unfortunately that means machine work to the heads, namely enlarging the spring pockets, on ANY stock heads.

 

The spring part # is RV943X if that help at all. Im just confused as to why it would take 9000km to wipe a lobe if the problem was coil bind.