Dropped compression
Turbo Mini Forums

So last weekend I decided to take the scamp out to my dads where I'm working on the next project , sun was shining etc etc ..

So coming around a sharp left hander I slowed right down in first gave myself some room and planted my right foot down , it came on boost lovely up to 16psi as set up and was pulling very well right up to 3rd when I noticed it started to go lean , like 13.2 on the AFR . I wacked the clutch in straight away and coasted to my dads with the AFR around 10 at 2k revs . When I got there I noticed a very slight misfire ( very slight) . I knew I had done something so did a compression test and found it 150-160 on all but 1 where it was 90 psi .

Head off you can see which piston is effected


So I also found the top heavy duty engine stabiliser had sheared off taking part of the box section frame with it along the seam.


I believe this had allowed the engine to rotate and crushed the main fuel line between the plenum and the bulk head as the braded fuel hose was flattened and left a mark on the bulk head and plenum .

unfortunatly it's not a head gasket as I have tried that, I did a fluid in the bore test and all seems ok. I have checked the head and valves and again all fine there . I suspect it's a ring but any other suggestions are welcome as I am slightly confused .

The plan now is to park it up and remove the engine at a later date , get it rebuilt ready for the GT2056 I have waiting and dump it in my next project . The scamp will then be another project poss with a k series .
So alsas I have to say goodnight to the scamp a little early this year

How did you check the head?
How does that bore surface look - any signs of trauma?
Have you compared the piston to deck heights to rule out a problem with the rod / journal / bearing ?

Edited by PhilR on 7th Aug, 2015.

I dropped the head in to my local engineering workshops and they pressure checked the valves and seals, I did measure the piston heights and all were equal , I based my ring guess on the fact that the AFR went lean . The engine will be stripped and rebuilt anyway but I wondered if fuel stavation would cause it to lean out that bad or could there be an issue with something else .

could be shagged ring lands, what pistons are they?

I'd say 10cc cast omega's.

If something is worth doing, it's worth doing half of.

Perhaps a chance of over-heated rings that lost their tension. But sadly I'd guess that's more likely on 4 or 1... Unless you've got oil jets (?) and No. 3 has gone bad.

Yes they are omega 10cc dish , and no oil jets . I guess the rebuild will tell .

In the meantime I have this to work on

How rich are you running if 13 is lean?...

14 at idle, 11ish on boost. You wouldn't damage an engine at idle no matter how the mixture is set, so I presume he's on about under load

He was at 16psi

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Yeah it's too lean at 16psi with full load , it should be 11 - 12 maybe even less .

Ah right ok

I have been really lazy and not done anything with this until today when I pulled the engine apart and found a crack in piston 3 between the rings . Before I go ordering a whole new set ( cant find individual ones ) does anyone have a new Omega Cast with a 10cc dish +0.20 (1293) they are willing to sell me ?

Cheers

I think MED may be able to supply them singly ?

Phil.

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