Help: No compression in valve 6

[DavidWeis]

Hi,

I own a 95 C280 with 180,000 miles. This weekend, on local highway drive I was testing the brakes and alignment, then accelerating back up to speed. After braking hard, the engine started to bog down.

A mechanic did a compression test, and found that there was only 15psi in cylinder 6. In Top Dead Center, he tried to pressurized the cylinder, and said he could hear the air going into the intake valve. He thinks that something is keeping the intake valve open.

Has anyone ever heard of this? What could it be?

Help:

Thanks

[gmercoleza]

Not too common, but could be broken intake valve spring.

Yep, it is rare but, I've seen broken valve springs before on 6 zylinder models. They get weak and break.

I would remove the valve cover next, and see what broke.

[DavidWeis]

By remove the valve cover, you mean the head?

Dave

[manny]

Originally Posted by DavidWeis

By remove the valve cover, you mean the head?
Dave

NO. The valve cover, to do a visual inspection, looking for possibly a broken valve spring.

Right, shouldn't take much effort or time. I think that motor is a M104 and the valve cover should come off quite easily. The suspect valve will have valve spring retainer that is lower than the others, indicating issues.

With the proper air hold device(the same one used to pressurize the cylinder), the broken spring can be replaced without removing the cylinder head.

Whoops, I forgot about that, it's a dohc, isn't it?

I wonder about valve float at high rpm's, after re-reading the first post.....

[Matt L]

Until you determine that it isn't a broken spring, don't run that engine. The broken pieces can bind and destroy other parts. I've seen the results before: worn cam lobe, destroyed lifter, mushroomed valve stem and destroyed valve guide. I didn't bother trying to get the guide and valve out of that head, and just threw the whole head away. For all I know, the hole for the guide in the casting was also deformed.

[manny]

Originally Posted by mbtechman

i seen carbon get stuck to the vavle seat before on a 104 motor .

Now THAT sounds realistic.
Given the circumstances described ( after hard acceleration ).
Run a can of good combustion chamber cleaner through it & see what happens.

[SootyPast]

Also, I have personally experienced a high mileage car with a sloppy chain skip a tooth under sever and abrupt braking. The inertia of the internal engine components want to keep going and the crank stops. Check cam timing. This could be what occured.