Koenig928

Lots o pictures here.

Got the Koenig engine completely apart now, found some interesting things I wasn't expecting. (and I was only going to replace a leaking head gasket...)

I knew it had a GTS crank before by measuring the stroke, which is 86mm (85.9mm), and I assumed it must have had GTS pistons as well. However, looking at the pistons with the head removed, they don't look like GTS pistons. The 'dish' is completly rounded out and they measure approximately 101mm (at the skirt, per the WSM)

Does anyone know what pistons these are? Also the cylinder bores all measure ~101mm as well... (according to my cheap-o measure stick)

Second problem, hole #5 is pretty beat up. Several deep gouge marks on the wall. I removed the piston thinking there was a broken ring or something, but the rings look in perfect condition. What would make these scratches in the cylinder wall?? Probably explains the oil smoking while running. Leakdown on this cylinder was actually pretty good (2%) with the piston at TDC, where the gouges stop. But makes sense to me now why it was crap when the piston was at any other positon.

What do you think my options are for cylinder #5 are? Bore it and put a larger piston (obviously), either custom made or 968?? (since the bore is already at 101mm). Or just leave it alone and run with it...?

All other cylinders looks to be in very good shape though.

Help please!!

slate blue

Hey Koenig, sorry for your trouble, I have to get you to do some investigation for me. Those rods and pistons aren't GTS. They are S4, I would also say that the crank is an S4 also. This will be easy to tell, just see if it is a fully counter weighted crank, if it is it is GTS if not S4. What is the engine no? I think the engine is a bitsa. The rods may be from an 87 S4 but the block doesn't have the squirters, they changed the rods when they went away from squirters in 87. Adam and Myself have an 87 engine and I'm sure he would back me up on this one.

So what to do, well, depending on your budget Mahle are making some very nice custom pistons, Lag posted some pictures of the custom pistons his friend had made and they were 4 inch. This would be good for your block, you would still need a bore but if Mahle would do that piston for less do to the fact they have it saved in their database that would be good for you. You will then need to change your rods and maybe you crank depending on what you want. I'm actually offset grinding my crank to stroke it and use chevy rods. They are cheap and some what plentiful on ebay. I will write more about this if you are interested.

Cheers Greg

Vilhuer

101mm would mean 2nd oversize which do not exist according to PET. Connecting rod are definitelly not GTS rods as there is 5,0 stamped in them. S4 pistons should have longer skirts but they can be of course removed.

Block could be repaired with Kolbenschmidt aluminium sleeve. Then you'd need 100mm piston what is (made to) similar shape as rest of them.
http://www.msi-motor-service.de/down...ren/alu_en.pdf

Koenig928

The engine block is a M28.42 / 81J 06781 (1988 year).

Here's what the crank looks like. The measured stroke is definetly ~86mm. I know the rods are stamped 5,0, which threw me off. But if crank was an S4 (5.0L), then the stroke should be 78.9mm (and its not).

Looks like Koenig did some custom work on this motor ~14 years ago. Not good for me though...

BC

Please do greg. I think with my GTS crank I have for the third motor it may be just as expensive to grind the crank and buy aftermarket rods for the chevy size as it would be to just have custom rods made. What do you think?

BTW - those pistons look very unusual - do you think they were ground down like Tony's?

Koenig928

It could be possible. Since the pistons did match anything in the WSM's, I thought they might have been 951 forged pistons. However, Tony doesn't think so because they don't resemble his 951 pistons he had ground down.

BC

951 pistons possibly came in an overside, but I thought oversizes werein .5mm increments? That would mean this is a second oversize?

Fastest928

GTS Piston with bowl mods just like mine!

Where did you get those?

Marc

Fastest928

GTS Piston with bowl mods just like mine!


Marc

Vilhuer

It's possible 2nd oversize was available but it's not listed in current PET and period tech spec book. Very strange.

Ian928

How about keeping the pistons, buy a cheap S4 block and bore to 101mm? That way you can keep your valauble GTS pistons, the cost of boring the block is the same anyway.

I have never seen a GTS piston, but the modifications look like the standard way of lowering compression by removing material from the piston.

slate blue

Hey guys, I did miss the lack of an extension of the skirt for it to be S4. Man that engine is really a bitsa. Very strange indeed, The reason I say that is the rod length is different from the GTS. To calculate the deck height, which from memory is 232mm deduct 150mm for the rod, half the stroke which is roughly 43mm and we are left with what must be the comp height of the piston. that equates to 39mm. I'm pretty sure that S4 is taller or bigger than that, so any body know the comp height of the GTS or 951?

Brendan, I did think they were ground down like Tony's but know have to reconsider. As I just mentioned need some comp heights. As to offset grinding Brendan, it costs $425 AUD here, or around $300 USD but there is also some welding involved and that is not cheap. But you could get what ever stroke you liked out off a GTS crank or atleast close to 8 mm more than standard. I only ever wanted a stroke of around 90 mm so as to not muck up the rod to stroke ratio.

Since you have a GTS crank it would be worthwhile I think, but when you start looking at the costs, I thought if I ever build my second motor I would just use a full custom crank. Because I was going to mod the oil pathways it starts to get expensive when you add it all up.

Motorsports of Utah has some great deals on rods, Olivers at I think $1100 or 1200, that would be the way to go if you just wanted to improve the rods.

Cheers Greg

BC

My GTS crank was, uh, pretty cheap, so it would be good for my ego to keep the costs low - Budget stroker/bored engine.
Chevy rod ends are what, 1.89? Was it 2.2? I forgot.

slate blue

Standard rod is 2.1" 2" is also available and I use 1.888" The standard porsche size is 52mm.

Cheers Greg

Tony

SECRET.


came with the motor..which came with the car.

Can you see lathe/machining marks on them Bill?
My machined pistons are from an S4 (below) the forged 951s have a differnt bowl shape. The 9 i have do atleast..more oval.