Bad compression on one cylinder, any ideas?

[PhatVR6 0]

hydraulic.

 

I have another head full of them

 

worth a try I suppose.

 

it really is running like a complete dog, it's as lumpy as hell.

 

I'll take the cams out completely and try the leak down test.

 

So much for going up to my parents for xmas :-(

[h100vw 0]

Could be one of the tappets is staying pumped and preventing the valve from seating.

[PhatVR6 0]

what would cause that?

[h100vw 0]

Bad luck mainly I think.

 

CVHs used to do it if you revved them too hard, it jammed in more oil than could escape. The tappet pumped up and held open the valves. All kinds of popping and banging went on until engine speed dropped enough for the oil to drain.

 

Old TomB had similar trouble on his 16V but the tappet went solid for some reason, the piston hit the sticking out valve and punched the cam off the head. It lifted the bearing cap off!!!

 

It's all guess work until you find the cause though. A quick over-rev might have caused a valve to touch a piston, doesn't take much to stop it seating 100%. I would imagine that they are pretty similarish inside to a KR. VW IMHO are just reinventing engines that they started with 30 years ago.. :lol:

 

You're an accomplished mechanic Paul, you'll get to the bottom of it.

Gavin

[PhatVR6 0]

There's certainly been no valve/piston contact at all.

 

it's so bloody frustrating!

[h100vw 0]

Apart from looking a bit mucky both pics look ok. Have you had the cams out to see if the valves are closing? I wonder if a broken/weak valve spring would stop the valve from sealing properly yet not cause any contact?

Gavin

[PhatVR6 0]

when the head was off I gave the cam a full rotation so i could see that they were closing, and also to see what the seats were like when they were open.

 

couldn't "see" anything untoward.

[h100vw 0]

Now we are clutching at straws then. :(

 

You still need to do the leak down, is that right?

 

I think that'll be the decider.

[PhatVR6 0]

yeah, I'll do that first thing in the morning.

 

if I can't decide what's happenign the head is coming off again.

 

I still have the original head. I'll clean that up and fit that.

[PhatVR6 0]

sorted it!

 

it was a broken exhaust valve spring!!

 

it'll take me all day to write down how I found that out, and how I replaced it without removing the head again, but if you want to know, say so and I'll do a write up.

 

I got a write up on 24v cam timing to do too.

[Supercharged 2]

Cool! - yep, write-up please!

[h100vw 0]

it was a broken exhaust valve spring!!

 

Get in!

 

Nice one Paul. Tell us all.

 

Gavin