Sump Compression Issues After Rebuild!

[rhysjones]

Hiya dudes,

Having considerable issues with my GT2 (weber carb) regarding sump compression leading to smoke and oil pouring out of the rocker chest breather.

I have only just rebuilt the engine after I had white oil smoke flying out of the exhaust and related running issues. Upon dismantle I found that the valve stem seals were knackered (common so I hear) and piston 4 had a lump broken off it between the rings, luckily it hadn't scored the cylinder. So I had the head refurbed, replaced the broken piston and put a new set of rings on all pistons and new big end shells. Even remembered to position the rings so that the gaps point away from each other and took the glaze off the cylinders for the new rings to bed in. Also put a new set of hydraulic tappets in too as start up used to be a bit noisy.

Rebuild went well, and initial running also ok. Noticed quickly that she was still quite smokey out of the rocker breather but put that down to oil being smothered everywhere during the rebuild. However only 300-400 miles in and I've got oil being thrown out of the breather pretty extensively. With the breather pipe being connected to the air intake, some oil goes through the carb and into the engine understandably giving me starting issues, and some oil leaks out of the air intake and burns off on the inlet and exhaust manifolds. Pinch the breather pipe and smoke/oil forces its way up the dipstick tube.

To add to it, while she is holding water, I do seem to keep finding white gunk on the dipstick too..... :( The new head gasket can't have gone already!?

This is every mechanics nightmare, and I'd love to know what's gone wrong... If anyone has any thoughts or ideas or advice that would be awesome and most welcome!

Cheers,
Rhys

[MRMENDER]

All the above Sound like Head gasket. Plus possibly a knackered piston too
Did you fit new head bolts?

[rhysjones]

Cheers for the reply,

Yeah fitted new head bolts. Have thought that after the running in period they may need tightening down a bit more? A possibility now I think of it is that the book specified they be tightened to the torque setting then a further 180degrees - but I could only get them to about 90degrees! Bloody tight! Take the rocker box off and give them another pull maybe?

Rhys

[MRMENDER]

NO NO NO!
If the HG has gone then tightening will only prolong the agony! Plus you may snap a bolt

[rhysjones]

Ha, righto.... I'll pull her apart again and have a look at the HG. (and order a new one plus new bolts). Any reason you can think of why it would have gone only a few weeks after being installed??

Rhys

[Chris M]

Before you rip it apart it might be worth checking to make sure the gauze in the cam cover breather is not blocked. A restriction here can cause oil to blow out of the breather. Also is the plastic black cover in place that sits between the cam cover and the camshaft?

[rhysjones]

Yeah plastic cover is in place and gauze is ok - but even if they weren't that wouldn't cause the smoke and sump compression problems.... Well pants

[james butler]

Sounds to me like you have too much blow by in the block overpressurising the crankcase.
Might be a result of your new rings and honed block? Which should go in time? Out of curiosity how did you "remove the glaze"?
It's been said a few times that these cars benefit from an oil catch can in the breather pipe so I wouldn't worry too much about it.

[rhysjones]

Ha, sounds a repair just up my street!

I removed the glaze by using a gadget with 3 stones sprung out that fitted in a cordless drill. Whizzed it up and down each cylinder 3 times as instructed by the lad I borrowed it from.

Done 500 miles since the rebuild so would have thought everything would have settled down by now.....

[sabre0699]

Did you put the rings on the pistons the correct way up ?

[rhysjones]

Yep, marks facing upwards

[MikeH]

When you say you de-glazed the bores, how did you do that? Did you check the ring gaps before you rebuilt it?

Sounds like you've got compression blowing past the

A couple of possibilities - the better scenario first.

1. if you're running semi or full synthetic oil to run the engine in, you could stop the rings from bedding in properly. Drop it and put old fashioned mineral oil in - ideally a thinner grade like SAE 30. Rings will bed in better on the overrun, as the vacuum of the engine pulls the rings square to the bore walls (I'm told), so moderate acceleration (no more than half throttle in any gear) followed by engine braking might help to bed the rings in.

2. It could be that the rings aren't bedding in because the bores aren't well enough honed, or that the rings aren't tight enough because of bore wear. Was there any sort of step in the top of the bores when you took it apart?

I've heard that the 'accepted wisdom' on VW iron block engines is that the bores need to be properly re-honed if you're changing the rings. I'm a big fan of proving that the 'accepted wisdom' is wrong though, especially where it costs a lot more money.

Mayo in the engine....
Head gaskets normally have torque instructions on the pack. Did you follow the tightening order and the torque instructions? If you're using a sensibly sized torque wrench (18-24") then you should have more than enough leverage. However, if you've left oil in the head bolt holes then there's nowhere for it to go, and you can hydraulic lock the bolts. It's possible to have the bolts go tight without clamping the gasket properly, and it's also possible to crack the block by trying to force the bolts in where there's oil in the bolt holes.

So did you clean the oil out of the holes? I definitely wouldn't go heaving at the bolts any harder, as you could trash the engine, after all that hard work. Patience is a good way to avoid making a problem a lot bigger (speaking from lots of experience of not being patient enough!).

I'd check your running in oil, do a compression test, and see what that tells you.

[rhysjones]

Hi Mike thanks for the reply,

The oil in the head bolt holes could well be a possibility! No I didn't clean any oil out of them when I dismantled - what would be the easiest method?? Roll up some tissue, dip in and soak up?

My torque wrench is about 12-14" long, 3/8 drive. Had no problem getting the bolts up to to torque, but to then turn them the required further 180degrees I used a 1/2" drive t-bar about 2ft long and could only sensibly manage 90degrees! Wimped out at that for fear of shearing them.

The oil I've used is sae grade Rubia 15w40 by Total... suitable enough i guess?? We get it by the barrel and ive always used it, although I'm not massively clued up on oils I'll admit! Does this sound ok?

I honed the bores by using a thing you put in a cordless drill - it had 3 long thin stones on 3 stalks held out by a series of springs. Had to squeeze it to put it in each cylinder then was instructed to spin and draw up and down 3 times fairly quickly.

No lips at top of bores indicating any wear and ring gaps spaces apart evenly too.

Cheers muchly,

Rhys

[rhysjones]

***ring gaps spaced apart evenly. (120degrees between each of the 3 rings)

[james butler]

this is why i asked about how you de-glazed the bores as it really easy to damage them, to be honest if i needed this doing i would take the block to a proper honing company because it only takes one deep scratch or slight oval ling of the bores to mess up the sealing ability of the rings.
i did look at the tool you used a while back for a job i was going to do but was advised then to take it to a specialist instead.
did you put he rings into the bores first and check the gap in the ring with a feeler guage? because it can tell you a lot, if you have a lot of wear or oval ling or ever taper to the bores.

to hone or even de-glaze the bores your after a very specific cross-hatch effect that usually requires a certain surface finish to retain oil and give the rings the best chance of bedding in, or at least that i was led to believe,which is why i think you now have so much crankcase pressure.

on the subject of head gasket do you get overpressuring of the expansion tank?
when my head gasket was going the expansion tank used to fizz with escaping air and if left running you could see a steady stream of bubbles in the expansion tank with the lid off coming through from the rad.