Advice needed: Bottom End Rebuild

[peterako]

Hi,

I would appreciate some advice regarding the pending rebuild of my 701 bottom end.

At present the pistons are at +30.

What are the pros and cons of:

Going to +40 versus reslieving and going back to standard pistons?

Many thanks in advance,
Peter

[JJDraper]

My original +2 block is at +60 (QED pistons) with no probs over the last 60k miles... Not sure which type it is as the casting has the prefix (to 6015) number ground out. It has a T4 number on the casting. Not sure why you would sleeve back to standard when there is meat left on the block. Is the 701 thinner walled?

Jeremy

[AHM]

Hi Peter,

Going from +30 to +40 is what I did last year.

Assuming that the engine was reasonably standard to start with, you get increased CR without takeing everything off the head. somewhere around 10:1 if you go back to standard you will have additional expense and reduce the CR.

you loose 40cc worth of power

You can buy cheap standard pistons to put in your expensive new sleeves though.

Sleeving is what you can do when the rebore to +40 doesn't work.

Simon

[peterako]

Many thanks guys,

Am also doing a head 'rebuild'. Parts ordered and hopefully on the way.

Think I may go the +40 route.

I have read on the forum that +60 is pushing it but generally +40 is fine.

Just being my usual procratinating self! (What I call 'thinking long and hard').

Take care,
Peter

[rgh0]

+40 thou to 83.5mm generally OK for most blocks. if you can find a machine shop to get the bores ultrasonically measured and offset the new bore to maximise and equalise the wall thickness as much as possible thats good to do. This minimises the risk of thin spots which is what typically causes a bore to subsequently split. It is also good to do because when you come to finally need resleeving you have maximum meat in the bore walls to allow the rebore for the sleeve insertion and you have sufficient wall thickness behind the sleeve after insertion to properly support the cleeve and stop it failing.

cheers
Rohan

[JJDraper]

You're getting me worried now! The rebore to +60 was done before I got the car, ten years or so ago. I've done head work, but never touched the bottom end. Should I treat the engine gently and save for sleeves before something happens?! Perhaps I'll start saving for a new block... Sad as the engine is the original for the car.

Jeremy

[rgh0]

You're getting me worried now! The rebore to +60 was done before I got the car, ten years or so ago. I've done head work, but never touched the bottom end. Should I treat the engine gently and save for sleeves before something happens?! Perhaps I'll start saving for a new block... Sad as the engine is the original for the car.

Jeremy

Hi jeremy
I would not worry to much. if your plus 60 thou overbore to 84 mm has been ok for 10 years then your cylinder walls are probably OK in thickness. it should be OK for a bore to 84.5 mm for a sleeve insertion and then bore the sleeve to std 82.5mm leaving a 1mm sleeve wall thickness. If you need it sleeved ever then try to get the walls of the cylinder ultrasonic measured for thickness and offset the boring to maximise and make as even as possible the wall thickness remaining behind the sleeve.

cheers
Rohan

[peterako]

Thanks Rohan.

[JJDraper]

Ditto, thanks Rohan..

Jeremy

[peterako]

Hi Guys,

OK....broken ring on No. 2 forces my rebuild forward.

I have decided to re-line go back to standard.

I know the following is a question for the engine builder but as I'll be ordering the liners fron the UK (westwood cylinder liners).....

How much of an intereference fit is required?

I can get flanged liners with OD 3.378".

My bores are currently (max width):

1 - 3.282"
2 - 3.285" (ring broke on this one)
3 - 3.283"
4 - 3.282"

All are pretty round.
Within one/two thousanths at other orientations per bore with the exception of no.2 with 4 thousanths at one orientation.

Can you foresee any obvious/blatent issues?

As always, advice is greatly apreciated and taken at face value.

I.e.....you don't have the block in front of you and cannot be expected to give definitive and exact advice

Take care,
Peter

[garyeanderson]

I would take it to a "qualified shop" and let them advise you, personally I would not liner a block until you have gone .040 over. If the block did nod pass inspection at .040 then I would liner the offending bores. The bore centers are 96mm or 3.78 inch with water between and taking all of that cast iron away to liner scares me.

Your call though.

Gary