cantresjr

ok, I'm contemplating the posibility of having to open the engine and needing some cylinder work. my questions are:

1) whats the max i can go on bore?

2) what special needs i have to take into consideration before or after boring?

3) what is the alusil treatment i've heard?

4) what questions to ask machine shop to make sure they are up to the task?

TIA

hosrom_951

I can answer 1 question.

The max you can go? you want to increase the bore ?

Stocks are either 100.00 or 100.50 (oversize, you need new pistons and rings).

You could go for 104.00mm for a 3.0l engine (special pistons needed)

Some people even got 106mm bore from the block, so what are you looking for to be exact?

cantresjr

just to know the max if I find any scoring on the cylinders. whats the biggest over size for factory pistons?.

104mm, hhmmm! the posibilities

hosrom_951

The max size is 100.50mm from the factory (i am in the process of getting pistons for some buddies of mine, and saw Porsche's specifications).

But you MAY want to go for 104.00mm low compression 8:1 pistons if you have DEEP heavy scorinng that would require more than 100.50mm overbore.

hosrom_951

By the way, Ski just recently overbored the engine on his race car to 100.50mm, you can ask him about the alusil treatments.

Mike B

This can get to be a very expensive proposition. If you want to go with original pistons then get ready to fork out about $1300 US for 100.5 plus machining costs. You could consider sleeving and using other pistons , like JE, but I would research the success rate further. When I went through this a couple years ago I couldn't find anybody who with a long term success story. Not saying they're not out there but I couldn't find them.

I went with factory oversize 100.5 pistons and took them to a local machine shop with the infamous Sunnen CK-10 machine. I gave them the specs from the factory service manuals and they did a great job. Cost me $400 Cdn total to bore, hone, etc my block. It works great! Doesn't burn anything that I can tell. Leaks...yes, I have ONE damn leak which I will fix this winter. Otherwise it runs great. I figure I'm good for about 20 more years

The factory service manuals spell the whole process out. Do you have a set?

cantresjr

I'm afraid I don't could you pm me. lets talk about options on getting those specs.

hosrom_951

Where in the manual? regarding the block specs right?

Tom M'Guinn

Hers's how I'd answer your questions:

1. No one knows for sure. Porsche endorses a 100.5 one-over size. The next size up for pistons is 104, which makes for a pretty thin cylinder...

2. Find the pistons first and have the cylinders cut to fit

3. just a special finishing process to bring out the right surface on the bores

4. Ask them if they have the special Sunnen machine and if they've done these motors before -- if they flinch at all, move on

hosrom_951

Are the 911 (993/964 air cooled) engines used the same Alusil walls as the 944?

Here, they rebuilt several 911's (aircooled) but NEVER did a 924/944/968 nor a 928 (basically water cooled).

Are the same (more or less) materials used the the Porsche engines?

cantresjr

Thanks tom.

how is the finishing process done. so i know if the machine shop is blowing hot air up my ...

MySwiss

The factory 100.5mm pistons that are available right now in the USA, are 1600$ and more for the set.

But we now have an alternative, that I have used personnaly,and that is to go with 100.5mm or 101mm aftermarket aluminum pistons, specifically built with the right coating, to correctly work with the 951 Alusil bore. I have used successfully the 100.5mm, and I'm now waiting to use the 101mm, in my new rebuild.

So we now have an afordable and better alternative for reusing are scored or badly scored Alusil block, for less the 1200$.

All you need to do , is to find a good machine shop that has the Sonnen products as well as the machine, to apply this Alusil paste into your block, once it's been machine to the factory specs.

If they can not get or use the Alusil paste, from Sonnen, then find a machine who can, unless you want to use the sleeving method.

hosrom_951

What kind of coating is needed on the aluminum pistons MySwiss?

This could be applied to JE pistons as well? as long as the coating is correct?

Ski

MySwiss - they work pretty good eh? We put the 100.5s in the track car too, seated in GREAT! I too am awaiting my 101s again because I let the vendor sell my set to a rennlister in need in CO.

There is an alternative now and MySwiss hit the price on the head. I will call the vendor in question tomorrow to see if his ready to put it out, as it has sort of been word of mouth and they have been flying off the shelf. 100mm, 100.5, 101mm are available for 944 and 951. 104mm and 104.5 for the S2 and 968.

Tom, Mike B, and MySwiss have pretty much answered the questions but the key is getting the pistons, which are iron coated on the skirts with a bit of graphite added to the coating. The tops of the pistons are thermal coated with a new type of plasma application. The rings are for alusil bores and I can attest to the good seating with wiping down the skirts ONLY and the cylinder walls with a LIGHT coat of 30wt, non-detergent dino oil, and run this for 100-150 miles. We had great vacuum, compression and less than 1% leakdown on the track car in 150 miles. We are still breaking in the track car but we're on 20/50 dino now and boost up to 12 at 300 miles.

Cantresjr, not sure if your in the military, but if you can get your block to San Antonio(AFB) we had ours done at Duffin Engine Service in San Antonio, who also did OZ951s engine; beautiful work - bore/straighten, hone, alusil treat & hone. The block reflects a .004 cleaning pass, they also checked our head which had just been done also, a little over $350 and they removed the old head studs!

cantresjr

WOW! it is a lot of work. well now i'm hoping that it's not a cylinder problem but a valve guide or something in the head.
how hard is it to find a good bare block. it might be better for downtime purposes, especially if i go the San Antonio route

yes I'm in the military and frequent San Antonio often.

Thanks to all