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Discussion Starter · #1 ·
Hello all,

Just looking for some advice from some experienced engine mechanics.

I purchased a GSi a while back, which had a full engine rebuild prior to me purchasing. I was running the engine in and it was running poor and misfiring and getting excessive oil vapour from the fitted oil catch can.

I did a compression test, which identified one cylinder at 0psi, one at 80psi and I believe the other two were around 175psi. I handed the car to my local mechanic who confirmed the compression test and sent the head away to a machine shop.

The machine shop identified two stem seals not seated / fitted correctly and reground valves, skimmed the head and handed me it back. The head was refitted by the garage and I was told to put around 1000 miles on the car and return to get the head bolts re-torqued. They also told me I would continue to get a lot of oil vapour from the catch can until the carbon builds up around the valves.

I?ve yet to check the compression (will do some point this week), but its definitely running on 4 cylinders now. I?ve put on around 700 miles and still getting excessive oil vapour from the catch can. When the cars at tickover the oil vapour is coming out the catch can filter like vapour out the exhaust pipe.

So I?m really looking for some advice as to if I?m doing the correct thing by putting on miles on in the hope the carbon builds up in the head. Reading in other forum some people state this builds up can take 4-5000 miles not 1000! (This is going to take me ages at the nova isn?t a daily driver) When this happens will this definitely reduce the blow by I?m getting into the crank and seeing the vapour coming from the catch van filter? Or should I be looking further down with the possibility of the rings not sealing or need the cylinders rehoned?

It?s driving me mad as the garage is just saying to drive it and it should sort it . Has anyone else had this kind of issue and when was the point where I should pull the trigger to tear it down in the hope of identifying the root cause?

Any help or advice appreciated, thanks
 

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I would suggest getting another compression test done, it should give you an idea of the state of the bottom end now the head had been done. Could be the rings were either not replaced during the 'rebuild' or just not correctly selected/gapped causing excessive blow-by.
 

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Discussion Starter · #3 ·
Thanks for the recommendation ayresyy. I've just done a compression test which has showed improvement but still appears fairly unhealthy. I've not got the Haynes in front of me but looking at the engine face on the plug order left to right shows, #1-180psi, #2-127psi, #3-135psi, #4-45psi.
Back to the garage it is then and a bottom end tear down I guess. Any idea of what I should expect to pay?
 

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It would be worth carrying out the same test again only wet i.e. stick a teaspoon full of oil down each plug hole before you compression test it. If the low compression is indeed caused by the rings, your results should improve quite a bit.

Are you confident in the garage you have been using?
 

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Discussion Starter · #5 ·
Hi ayresyy,

Just carried out a wet compression test and as your said I saw a huge improvement with the oil sealing the rings to the cylinder.

Cold & Dry Test Cold & Wet (5mm of oil) Improvement
1 - 180psi 1 - 215psi + 17% improvement
2- 127psi 2 - 167psi + 27% improvement
3- 135psi 3 - 163psi + 19% improvement
4- 45psi 4 - 73psi + 47% improvement

The garage I'm using is one I've used for many years and the chap owns the garage and is 30+ years in the trade. He offered to do it on the side and would be done for cash. I don't think he's going to rip me off or anything but I would just like this sorted quicker as it took him 2 months or so to get round to checking the compression etc. He's built, restored and owns a load of old fords sodas know his stuff. I don't really know any other places locally I could take the car to that I feel wouldn't likely take the piss.

Can you suggest any other tests that can be tried to further point to the rings or bottom end?
 

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With readings still that low and so varied, it looks like its time for another strip down. If you are confident the head was rebuilt correctly (pressure tested?), then you are obviously left with a bottom end issue. It looks most likely that the rings are at fault.
 
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