cylinder bore tolerances?

Well you have to measure and see if you can clean it up with the hone if you can remove more material. I am not a fan of ball hones because they don't true the bores. I use a lisle fixed stone hone that will true the bores back up. You can fix a bad bore if you have enough material left. Heck, I bored a block 1st over with it using the coarse stones, took a while but worked well.

You can run up to around 4-5 thou of piston to bore clearance and it will run fine. 2 or less is better though.

I agree with Trubocharged, except for the maximum clearance. .005" is a recipe for blowby, which isn't that much of a problem to alleviate, the way we do it. Of course, the ball hone is only to remove the glazing of the cylinder walls. If you don't deglaze, it takes 10,000 miles to get new rings to break-in.

But as I mentioned earlier in this thread, DO NOT depend on the numbers shown in the Bentley book, because the dimension piston they developed clearances from are 94.47mm or 3.130". The actual stock size of almost every engine, barring just a few is 79.44mm or 3.12756". Now, you may think I'm splitting hairs and truthfully that is what needs to be done. If you bore according to the Bentley and add the usual .0015" clearance for the piston, you missed the proper clearance by .001". That doesn't seem like much, until you figure, .0025", the clearance you actually have, is only .001" to what I refer to as 'wear out' limit. We do have a set of rings that are 79.51mm or 3.1303". On occasion, we get really well maintained block, hone it for taper and out of round, coat our stock pistons .003"-.004" and put it together. Same pistons, slightly larger rings, very close to stock bore size. It's a minimally invasive rebuild

1986.5 Supra, That is one of the reasons to get rid of the BEW glow plugs. If something hits them, they shatter like glass.

The ALH pistons in my Golf measure between 79.42 and 79.43 mm, didn't get the chance to measure the bores for out of round and taper as I dont have a micrometer yet. The cylinders do have some line marks and the cross hatch is barely visible anymore and I can barely catch my nail in the lines, they seem pretty smooth. Could I get away with only a simple stone hone with block still in car and 79.51mm rings all over if the bores measure out ok?

Gvr, Sorry for the slow response. As usual, a LOT going on....

This becomes a 'feel' thing. Accurate measurements and temperature, strangely enough, make an impressive difference. If you can catch your fingernail on a vertical stripe in the cylinder, expect oil usage. I won't build like that. I know the impulse is to 'cheat' and try another set of slight oversize piston rings, but we live by simple rules...'Do It Once and Do It Right.' 'Build It Like You're Gonna Buy It.' It may not be the cheap route, but the results are worth it. We do not like piston slap, as that is the reduction of the rings and cylinder walls life expectancy.

With the existing pistons at around 79.42, they are slightly worn and so is the block. I doubt the 79.51mm rings will work. Hone the block until squared up for Out of Round and taper. End gap 1st oversize rings to fit. Coat the pistons for .0015" clearance. I know I'm mixing metaphors, MM and Inches. 79.44mm is 3.1276". 79.51mm = 3.130". That is .0024" difference. That doesn't sound like much until your figure the engines we blueprint, we are using .0012" piston/ Cylinder wall clearance. Just the piston wear is double that. You probably need to hone larger than 79.51mm to clean up the cylinder walls in your situation. Although there are not pistons that are .010" (.25mm) oversize, we have the 1st oversize rings and coat the pistons to fit.

When we are using existing pistons, they are recoated with the graphite to fit with the bore. The slightly oversize rings CAN be a really cool trick, but the cylinder wear is a close tolerance when using the 79.51mm rings. Sometimes, we have to hone to an even larger size. We have done .010" (first oversize) rings and coated pistons to work.

The claim is that coating can be done to .020", but that seems excessive to me. If that is what is needed, I think using 2nd oversize pistons is the way to go. That is, if you can find them. We stick with Nural, Kolbenschmidt or Mahle, which seem to have been wiped out in the market for the time being.

The 'outsourced' pistons, I am no fan. If that's what it comes to, I'm retired. What Hans sells, I won't install. No way. Stuff from Saudi Arabia or the CRAP from China, like Engine Team; Nope... I'm not going to 'bottom feed' :/ The tolerances are not there. Piston weights vary too much. I don't trust the metallurgy. Other than that, they might be fine... LOL!

Hi Franko, I would really like to do this rebuild once and right, but I was not quite prepared to take the pistons out, and neither was my wallet tbh.
After spending some time with the engine, I can't actually catch my nail in 90% of the grooves left in the cylinder walls, I can slightly catch it in some though.
Measured the pistons with a good micrometer, all 4 of them measured 79.41mm. True enough, the block shows it's wear and tear as I've taken measurements with a bore gauge and found IDs up to 79.56mm . I'm used to metrics so that's what I'm using, but I can always convert inches to mm with the help of the good ol google. I would really like to send the pistons to you to have them recoated with the graphite coating, but I'm placed in Europe, so yeah.. Would I be able to re ring with the 79.51 and hone with those loose tolerances to make the car run ok for a year until I get enough savings to do it right with good parts and methods? If not, then I'll be looking for another bottom end as it's cheaper than rebuilding this one with new pistons.
Also, I'm very curious about the ALH bore size with the 79.44mm standard pistons. Is it the same 79.51mm bore as with the 79.47 standard pistons? With 79.47 pistons/79.51mm bore, that is 0.04mm clearance. With 79.44 pistons/79.51mm bore, it's 0.07mm piston to cylinder clearance. Is this correct? I am sorry if I come out as dumb here, but I don't have a manual ( yet ) and I'm taking info from wherever possible.
Also also, any big differences between the Nural , KS and Mahle pistons ? Been searching for the recipe of a rebuild for some time, still trying to wrap my head around all the engine rebuilding practice as I have not tried it at this scale yet.

Your question of doing it just good enough to get by and doing over correctly later leads me to suggest another running engine. Then you can rebuild this one correctly at the pace your budget allows and install when completed

Gvr and Jmodge,

I have been very particular when it comes to the builds I do. What Jodge thinks is probably a very good idea, as I've seen lots of motors that were in better shape than the one you currently have. But I am not ignorant about the cost of things in Romania. Sometimes, you have to get by. I do not think using the ring sets I have would do anything good for you. Scratches in the cylinder walls are NEVER acceptable. Oil burning will be a part of the predicament, and eventually, you will be stopping to 'fill the oil and check the fuel'.

If you were to see what engine I just finished, Grv, I think you would be shocked and what it cost. However, I think you might find a way out, just not the normal routes. You might be best to find a wrecked car. I hope you can find something appropriate.

Thank you all, been thinking just about that as there are enough used engines around here. Will take this engine out and slowly build it with quality parts.
Any suggestions on piston and bearing brands to go with?