Car trouble at combe
Turbo Mini Forums

As some of you may know, i had a bit of trouble with the car at combe, firstly, i blew a head gasket on its first outing, fitted a bk450 gasket and the car seemed good, actually better than its ever felt, went out again at around 4pm, was going along the start finish straight, albeit quiet quickly, and i heard two very loud sort of knocks from the engine, i backed off and cruised it round to the pit lane as it felt like it was on 3 cylinders. Got back to the stand and had a look at the engine and it was breathing quite heavily through the oil cap and breathers. Now, tomorrow, i'm gonna strip it down and find out what wrong, so, anyone got any ideas it could be?, i have a feeling it was detonation but having never experienced it before, i'm not too sure what it sounds or feels like.
Best guesses everyone.

Keith

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Did you change the oil when the gasket blew?
Does it knock or smoke when running?

no, oil looked like new, the head gasket blew from number 4 cylinder to the outside of the head, we could see exhaust gasses escaping between the block and head. Theres no smoke from the exhaust and no knocks, just smoke from the breathers and oil cap, feels like its running on 3 plugs too.

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Hi,
Compression test first, leak down test if needs be. Could be rings/lands/pistons :(
Cheers,
Gavin :)

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ok, so, do the compression test, then squirt oil in bores and do again, if reading goes up it rings or piston problem, if it stays the same its valve or head problem, have i got that right?.

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Spot on :)

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

Visit www.doyouneedabrain.co.uk

My Mini build diary

iam afraid it could be the ring lands

Well, the prognosis is not good. Stripped the head off again, number 4 cylinder is completely knackered. After refitting a head gasket at combe, it looks like the fan blades yet again are to blame for a complete engine melt down. It has chewed its way through the actuator pipe not allowing the wastegate to open, when i went down the start finish straight toward folly its overboosted and blown number 4 and 3 piston. looks like a complete stripdown and repair.
The BK450 head gasket was in perfect condition, looks like Mr Benross has got it on the money, lots of ally deposits all over the top edge of the piston and valves on number 4 cylinder.

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Oh dear. This is a good reason to keep the overboost valve in the plenum, with a stronger spring fitted.

Bad news, looks like an expensive fix but is the bore undamaged ???

Looks fairly low mileage from what I can see of No 3 bore in the photo and how clean the crown of No 4 is (but maybe you cleaned it when changing the head gasket).

What make of piston are they ???

Schrödinger's cat - so which one am I ???

they are omega turbo pistons, they look pretty clean and your right, its only done about 100 miles.honing is still there. i'll post some more hi res pictures and some of the head, another note to mention was the figures from the compression test
no 4 30psi
no 3 50psi
no 2 175psi
no 1 200psi
very alarming figures especially number 1, should have really got myself another gauge to double check, i have never seen such high compression in any engine, this was supposed to be around 8.1 by the engine builder.

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Unlucky mate! Saw the car last weekend and it looked great.

Are they forged or cast omega's?

hopefully you will get away with the pistons and new rings ..... if the bores are ok ? just rough them up a shade with a honing tool

good luck and sort that dam actuator pipe out of the way

Edited by BENROSS on 2nd Oct, 2008.

I know this could start all sorts of arguements as to what you can tell the actual CR is from a compression test (there is no direct correlation, because of choice of cam etc...) but, yes, 200 is way too high for 8:1
I would even say 175 is too high.

I would suggest you do a volume check of the dish and deck volume (burette, parafin etc) on the sound pistons with them at TDC before you strip it (and obviously the head) to see what CR you actually have/had.

Schrödinger's cat - so which one am I ???

yeh Rod i'll do that just to put my mind at rest, maybe the head has been skimmed too much, I forsee a call to Benross.
Some more pictures taken, sorry they are not good quality as i am losing the light.

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

4th photo down, can't quite read the piston (dish) volume... is it 10, 12 or 18cc ???

The head doesn't look like the chambers have been enlarged (although, again, photos can be deceptive). so the chambers may be 22cc or less if it's been skimmed.

The reason I'm so interested is that I've just machined a set of hypatecs to 14cc dish and I calculate that I still need 28cc in the head to get 8:1 (albeit on a 1360 engine).

Schrödinger's cat - so which one am I ???

im going to go for rings. there is alot of oil on the head, but the bore looks ok from what i can see.

and im trying to be optimistic!!

Chambers look, standard. So even if the pistons are 18cc you're compression won't be 8-1.
I'd measure the chambers properly if i was you, even from the factory i've measured chambers as small as 19cc in a standard head.

WWW.TURBO-MINI.COM

yes they are standard chamber shape and maybe less as the guys point out if the head has been flashed!

whats the over bore and cc in the pistons

1293 10cc dished

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Edited by Rod S on 2nd Oct, 2008.

Schrödinger's cat - so which one am I ???

with a std head (21.4cc?) thats about 9.8-1!

28cc wil give about 8.5-1

for 8-1 you'll need 30 and a bit cc chambers

Oops, Joe got in while I was editing.
Luckily he says the same.... 10cc in pistons requires 30cc in head (plus all the other bits) for 8:1

Schrödinger's cat - so which one am I ???

BENROSSSSS!!!!!!!!!!

133.5 bhp 123 lb torque 116mph @6640rpm 9.5psi
Shakespear RWYB 14.995 91.83mph

Found the link....

http://www.afracing.co.uk/CR.xls

Use it.

Schrödinger's cat - so which one am I ???