A+ Cranks.
Turbo Mini Forums

Right as some of you are aware. I’ve had a bit of an oil pressure issue with my motor. Starting of fine 65psi then falling to about 20-15 after about 5 mins.

So I've pulled it apart and everything is in order apart from the crank. It looks like its done about 150.000 miles. When it's actually only done about 350 slow miles.

The mains are nearly through the white metal. and the crank has worn to the same extent. It was 10 thuo under to start with. but now it would require the max 40 thro just to get it useable again.

There are no signs of excess heat or contamination. The cam, engine bores and oil pump all look fine to.

So can it just be that with a relative high compression ratio and stock crank that’s it worn itself out super fast.

The engine turn over fine when built and all new components were used. I still have all the blue print info of the build.

Crank was a stock MG metro 1275 A+ item. with just a regrind. The crank has had no other treatment.

Are these cranks made out of fudge...?

I'll post some pics later for all to see.

Si

I drill holes in everything..!

Si, you say down to the bearing backing, i take it the journals are badly scored , if this is the case it was debris and shite in the oil ways [ iron fillings] that has done the damage, snowball effect,

carl

high comp will not do any damage

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Would incorrect clearances to start with cause this?

Carl,

I must get some pics up for you. But everything looks clean. Not like its picked anything up. The crank has a mirror image of the shells worn into it. No scoring or heat. The oil ways in the crank are clear to. But I will look deeper to see what I can find.

You'd think the pump would tell the story but on first inspection look fine.

Thought at first that it might be bent, and put extra load on onto the bearings.

But I can say hand on heart that it was'nt when it went in.

Si

I drill holes in everything..!

What shells are they?
Where did they come from?

I seriously doubt it!

Oil gallery core plugs fitted too deep?

Paul, I'll check my notes..

Oil gallery core plugs were drilled and taped with new threaded plugs. But will check that area to.

Si

I drill holes in everything..!

is this mains or big ends, or both?

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Mains Carl,

Big ends are bad but know were near as bad as the mains.

Si

I drill holes in everything..!

Pictures!!

pictures of the oil gallery plugs too

Edited by Sprocket on 30th Dec, 2009.

could be down to the regrind an depends who done it.

i still use a bog standard one with no regrind at the moment.

several race engine builders who i spoke to said check on a lathe with a dti and check journels if with in tolerence then leave alone.

mine had less than 1 thou discrepancy so i left alone and all my cranks have neen fine. sometimes the grinders just bang them out with out properly checking the clearances.

one guy sent a crank of for a regrind to a reputal machine shop and came back worse than he sent in the deflaction check on the mains so always be carefull.

always looking for them bigger bunches of bannanas

Crank was done by Drakes in Bradford.

Who are very well know and of good reputation.

I promise pics tomorrow. and pics of plugs for Sprocket.

Si

Edited by Si P on 30th Dec, 2009.

I drill holes in everything..!

i don't think its possible to knock the standard gallery bungs in too far, they should hit a shoulder before getting anywhere near a takeoff.

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Thats whats funny,

I thought if it was a shortage of oil the crank would of started to dis colour. or even spin a bearing. But theres no sign of heat build up.

Si

I drill holes in everything..!

If anything should have spun a bearing, it should have been mine lol

Just shows how stubborn these little engines are.

I drill holes in everything..!

I always fit allen plugs to the oil ways, and on one side of the block, you need to be very careful not to fit a too long one. This WILL decrease/hinder the oil flow.

Did you plastigage the crank when fitting?

Heres the pics at last.

What do you think.?


Blown Crank.

Rear Main Crank Journal.

Rear main Bearing Shell

Centre Main Crank Journal

Centre Main Bearing Shell

Front Main Bearing Shell
And as Vegard mentioned above. Heres the plugs ( Sprocket ).


Allen Screw Gallery Plug

Gallery Plug Length
O and it just goes to show how long it was when I built it. Its actually a turbo crank.

Si

I drill holes in everything..!

That is contamination im afraid. But in all honesty, they dont look that bad.

Did you plastigauge the clearancies before you assembled it?

Edited by Sprocket on 9th Jan, 2010.

This is what I thought you were talking about

No, not that bad Sprocket. But worn in super quick time.

When you say contamination what do you actually mean? Foreign bodies or oil break down.

Because I've not found any real muck in the box or block ( oil galleries ) or any sign of anything broken.

No Plastigauge used at the time of rebuild. Just old school measurement techniques.

I have spent an hour examining the block and oil ways etc and have measured the rear main oil feed drilling in the block its 14mm from the block end face as per normal pre A+ blocks, however when I come to check the drilling by pushing a flexible tie wrap up from the rear main bearing its difficult to do. Almost as if there is a miss match with the feed hole's?? I’m not sure if this is because of the relief valve drilling (where the ball and spring is located) but I have another block which I will measure for a back to back comparison of this feature. The other main oil gallery to main bearing holes are perfectly clear both on the centre main and front journals???.

The search goes on. I don't just want to rebuild it and screw up yet another crank.

Si

I drill holes in everything..!

You can see particulate material embeded in the bearing surface and light scoring marks indicating that debris has entered the bearing at high speed. This could be from machining processes on either the block or the crank.

I spend at least an hour just cleaning the oil galleries with tube brushes, paraffin, parafin gun and compressed air until the parafin runs clean.
What other method is there to measure the clearance in bearing journals other than the age old plastiguage?

Also, please clarify one of your initial statements. "Starting of fine 65psi then falling to about 20-15 after about 5 mins" was this from cold? This could indicate that the engine clearancies were large to begin with, oil pressure dropping as the oil viscosity drops as it heats up.

Also, if that is a Pukka Turbo crank it will be hardened, and would not wear so much to require another 0.030" grind to clean it up. Having said that, the 0.010" grind might have removed the hardened surface.

The failure I had even though the bearing clearance was measurable in mm oil pressure was still good even at idle, which is why I was initialy unsure what the problem was. I am using a trubo capacity pump though.
Also have a look at the document attached

Attachments:

1007.35kb

While its in bits, might as well throw another oil pump in as a precaution.