Well, grey smoke from a 1275 is not a rare sight, but if I add up that the engine has been just recently reconditioned, and only run about 1 hour

The engine:
- early GT crank.
- velded (was cracked between the cyl. no 2 and 3) and sleeved back to std size
- new AE pistons
- clutch-cover breather
- new cam (SW5) and followers

The sympthoms:

- the engine starts on the button, and is running firm, smooth - just ok.
- perfect oil pressure
- when cold, no smoke
- when the oil warm up, it start to smoke grey - it gets very heavy if You turn up the revs.
- the exhaust gets oily
- the oil have turned brown in a short time
- we have some gass from the clutch breather
- after about half an hour running lots of oil on the pistons, in the cylinder head, in the inlet manifold, in the exhaust.
- cyl pressure 14-15 bar.

What I did:
- removed the breather hose
- changed the fuel type
- changed the oil ype (15W41, 20W50)
- replaced the head (reconditioned, new)
- replaced the head gasket
- replaced the piston rings (AE first, now NPP)
- measured the bores, looks all right

And now I am at the end of my ideas...

Gray Smoke is usually Fuel from being over rich.

Sounds like you have some high crankcase pressure too due to the smoke coming from the breathers and oil In the inlet/on pistons.


Did you measure the piston to bore clearance and set the ring gaps correctly? sounds like it is breathing past the rings/pistons. The compression test however indicates the seal is pretty good.

How much running in total has the engine done since rebuild.


Neil

Sounds bad enough to be a broken ring or two.

Definitely oil getting up into the combustion chambers and gases getting down into the crankcase.

"Did you measure the piston to bore clearance and set the ring gaps correctly?"

With the AE ringset, the gaps were measured between 0.5-0.8. At second I have bought a set of Toyota rings (71mms) and adjusted it to 0.30-top ring, 0.25 2nd ring, 0.35 3rd ring.

The smoke was the same.

I think the compression tester is fauled by the amount of oil present on the cylinder bores/chamber.

I have tried to measure the piston-bore clearance, but I have not much experience doing soo.

Although I have the right equipment (micrometers etc). If You can tell me how to do it, I will.

I am just gathering my strenght to take the engine out (3rd time ).

No broken ring for sure - I have replaced them once - the AE ringset was looking perfect.

All of the pistons are oily. Only no 1 and 4 slightly worse than no 2 and 3.

The engine had about 1.5 hours of running (idle, high idle (2000-3000).

Just so we are clear are these mesurements mm, the 0.5-0.8 of your first are very large, I run a larger bore than you 82mm on my Honda and built with heat in mind Nitrous etc and my Ring gaps are around 0.4mm from memory. A smaller bore will use smaller ring gaps.

Did you hone the bores before fitting hte new rings?

Can You get the right rings for the pistons, i.e not toyota as these may be the thickness to work correctly.

Easiest way for you to measure the piston to wall clearance will be with the piston in the bore and trying to slide a Feeler gauge between the Bore and Piston skirt, this may be easier with the rings removed, that will give you a quick indication as I doubt you will have acces to an internal micometer/or bore gauge. If you do this will be better.

Neil

Yes, sorry the measurements are in mms . Sorry this may be obvious for me, but not for You Englishmen.

The engine was sleeved bact to std size. It was bored and honed by the workshop.

the Toyota rings are the same thickness as the original AE (1.5,1.5,3). But the problem was the same with the AE rings.

I do have an internal bore gauge, but I do not have experiance with it.

How should I use it to measure size and not ovality?

Is there any way to measure bore - crankshaft angle? (should be 90 degree) Or bore paralelity?

What happens if you put the pistons in the bore 180 degrees turned?

The script on the pistons are facing towards the bulkhead...

Engine out, dismantled again.

I have managed to measure the pistons and the bores.

At the bottom of the skirt, I have measured theese:

cyl1: +0.05-0.068
cyl2: +0.07-0.085
cyl3: +0.073-0.092
cyl4: +0.055-0.07

Factory data: 0.048-0.065

No 2 and 3 is out of the measurements... maybe...

I have found theese marks on the cylinder.



Heat-seizing?

Are there any corresponding marks, raised edges or anything on the piston?

By the look of those cylinder heads you are obviously burning massive amounts of oil.

If it's not coming up from the sump the only alternative is that it's coming down through the valve guides.

If thats the honing then whoever did it needs to be shot

Yes. But what's causing the vertical marks after such a short running time?