1275 S engine build questions

[rolesyboy]

Hi Folks, I have started my 1275 S engine build and whilst it is in generally good order I have torn it down and started again.

It has been fitted many years ago with AE 431 plus 30 pistons. The rings and oil control rings are a bit graunchy and are in need of some TLC.

1) I wondered if you can still buy these rings in this size (I only ever seem to see them in increments of 20 thou??)

2) What should the ring gaps be on the aforementioned pistons?

3) Although I am unlikely to deck the block (as 163 head needs a fair bit off it) what should the block height be for a thin flange 1275 S block?

4) What is the Piston to bore clearance meant to be?

5) Replacing the Rod bolts- Any recommended suppliers/makes?

6) What should the squish or protusion of the pistons be? (.25mm if memory serves me right?)

Thanks in advance

Mark

[Spider]

I do have a current listing that these rings are available. Might have to ask around and possibly have your favorite supplier get them in.

Ring Gaps can depend on application, however 0.012 - 0.015" will be safe.

I wouldn't suggest less than 0.0025" Piston to bore clearance, again, it does depend on what the final application is.

I have been using stock rod bolts from one of the bigger suppliers, however I have been finding in recent times that as supplied, the threads are often knocked about. As the threads on these are (or should be!) rolled, not cut, it's not wise to clean them up with a die. The nuts so far, have been fine. Perhaps if the packaging was better on the bolts,,,

The only alternative I would recommend would be ARPs, which I think seem a little long for the small journal rods and seem a little on the 'fat' side in the big journal rods. There maybe other decent bolts about too.

Always have the rods closed and honed after fitting new rod bolts.

[rolesyboy]

If I had a crystal ball I would have been right. Spider to my rescue. Top man Spider.
The pistons are AE431 by the way. Anybody know anything about these? Cheers

[Spider]

Thanks for the kind comments there Rolesy

I don't have a listing on those, I've had a decent look though what I have (left ), I'll flick off an email to our AE supplier and see what he comes back with.

Which actually has me thinking, I'm wondering if these are imperial pistons, as about 10 years ago, AE metricated their pistons. Usually not an issue, however the new rings are a true metric thickness now and don't interchange with the earlier imperial pistons. I should have bought this up in my first posting It appears at this time, AE are the only manufacturer that have gone this way with our pistons, so for late AE pistons, you are also locked in to using their rings.

So, if they turn out to be imperial pistons, or rather, ring pack, Grant have ring sets available, in increments of 0.010" up to +0.040", then they jump to +0.060" (I've never seen a +0.050" piston in any case, not to say they aren't out there). They also have them in plain Cast Iron or Chrome. I use a lot of their rings these days and have found them very good, especially their Chrome sets, however, keep in mind that a good ring set cannot compensate for a bad bore or bad / inappropriate bore finish.

http://www.grantpistonrings.com/catalog/index.php

[251 ENG]

Are you sure they are not AEG 431 pistons ?

[rolesyboy]

Hi 251. Pretty certain they are AE431. The number is cast on the reverse of the crown (above the gudgeon pin as you look inside the pistonif you like).
I think AEG 431 are early 1275GT and stamped in the top of the piston in small letters IIRC???
Will check in the morning though. Thanks for your comments either way.

Spider- The engine was last rebuilt in 1973 and so from what you say you are most likely right. I will put a micrometer across the pistons tomorrow and check if they are any good. If they are I wouldnt mind dropping you a PM for a bit of advice on ring sets.

Cheers. Mark

[Spider]

Ah, OK, they will be imperial for sure then.

Try your supplier for the Grant Rings.

Sure you don't want to re-bore it?

[Spider]

OK, I've received this back from our AE Agent;-

"Has the piston got any numbers up inside the skirt?. AE431 doesn't mean anything to us."

So???

[rolesyboy]

Oops naughty step for me. Should say AE413 with H6 or HG on the inside. Cheers. Mark