Big AL in VA

According to my parts micro fiche. The 82 m28 11/12 have the same pistons as the 84 euro m28 21/22. My engine is the M28/22. My 84 has the twin distributor LH injection system. The car ID has the "ZZZ" deignating it as a EURO.

Hope this helps with the piston quandry.

Big AL from Virginia
84 928S Euro twin distributor monster

mark kibort

so, someone must know why this 84 euro has the early pistons. since all the heads are the same, how would an 84 have a greater compression ratio?
did some of the early 84s use the early 83 deep cut pistons?
Ive seen both and they both are quite differernt.

the real puzzle is how you were loosing coolent after the screw squashing. where was it coming out? top of the heads, at the gasket?
maybe the impact made a tunnel out the side of the impact area, im sure it doesnt take much with an aluminum head

I would check to see if they are warped or have a issue near the cyl. 4 area.

mk

hacker-pschorr

Could be - I just looked, I never took a good pic of my pistons when the heads were off.

Has anyone thrown out the idea this is not the original motor? Any lower end will work with the Euro S upper end & injection system. After 25+ years hard to tell what is original.

Ian928

I believe Richard has answered the question about the piston cut-outs. I think it is a probable scenario that Porsche used up the low compression pistons before putting in the true S2 ones.

My suggestion is to shave the heads to get to S2 compression spec. It's a win/win situation, you are sure both heads are straight, and you get a crisper engine and probably a few ponies more.

Ian in Norway

Big AL in VA

I will have the machine shop shave off .1mm +/- .03 mm. Off both heads.

Thanks, AL

BIG AL from Virginia
84 928S Euro twin distributor monster

Big AL in VA

Here is the picture of the same damaged head shown in my previous post now repaired. Both heads were ported, polished, 3 angle valve grind, scotch brighted and of course shaved. Total cost for me 1020.00. Done by C and C machinie shop in Manassas Virginia.


Big AL
84 928S Twin Distributor monster

Big AL in VA

Now I am starting to chase all the threads in the heads. I purchased a engine cleaning brush set from JEGS and thread chasers from Snap ON tools. I found a feeling of grit in the threads on my first 2 passes with a chaser. Each time I cleaned the threads.
Before chasing the threads I would run a brush inside the hole after spraying a little wd40 on the brush. After several passes with the brush and chaser the threads would cleanly accept the chaser without resistance.

Big Al
84 928S Euro twin distributor monster

mark kibort

Big Al,

if the pistons are not different, which they are, how could the compression be different between the 82s and 84 euros? since i have a piston in my hand from 82 and have had another one from 84, i can tell you that there are different pistons. the 84s (i had in my hand) had 2cc piston valve reliefs, vs the 82 8 6cc cuts you will measure with the older euro pistons

do you have any pics of the euro 84 pistons now that the heads are off? do you know that they are original?

Mk

Big AL in VA

Hi Mark,

I am sorry I can not answer your question. I want to find out for myself. When I have some time to look into this I will let you know. I, unfortunatly do not have a complete history of this car. Only that the plate on the engine desiganates it as a M28/22. Also, the VIN is a euro. Unless Porsche used some different pistons for some reason.

Big AL from Virginia
84 928S Euro twin distributor monster

Richard S

When I disassembled my 84 Euro S engine at Devek, the pistons were clearly different than the new-in-box 84-85 Euro S set Marc had. So Susan looked into it, and PET showed that approximately the first 600 84 Euro S engines used the left over 83 Euro S pistons, then changed to the regular 84 Euro S pistons. My engine was about 50 away from getting the newer pistons.

Hope this helps.

Rich

docmirror

If you're going to leave that piston in the bore, after prying out the screw, I would radius the sharp edges with a dremel. You may eventually get a burn through from overheating and thin-ness at that location. If you are going to replace it, I would recommend an exact match to the rest of the pistons, what ever style it is. I think your coolant came from ballooning the head in that location when the screw was pushed into it. something had to give, and it was the head. Hope the rod is okay. If you take the pan off, and push the piston out, you can change it, prep the cylinder and check or replace your rod. Cross member has to come off for the pan to come off. More work, but piece of mind.

Doc

mark kibort

clearly different as in the valve cut out reliefs? if so,this makes sense. however, if porsche was claiming 10.5:1 compression vs the 83's 10:1, i wonder if they just "jipped"everyone and maybe the hp for those were shy of the 310 rating, until they were fitted with the shallow cut out 84S euro pistons.

Mk

Richard S

Yes, obvious difference in the valve cut reliefs.

Rich

Big AL in VA

Here is the screw after being shark bitten.
I was very happy with the machine shop services. They returned all parts including the bad exhaust valve and of course the screw which found its way into the head.

Big AL from Virginia
84 928S euro twin distributor monster with possible 82 pistons

Big AL in VA

Here are two pictures illustrating the procedure for removing sharp burrs from the imprint on #4 piston head. Leaving these sharp burrs would cause pre-ignition. The sharp edges would begin to glow red hot thereby igniting the fuel air mixture.

The piston head is bordered by duct seal. A clay like substance that will capture all the metal particles.

I must give credit where credit is due. This procedure was given to me by Buddy Garret. An excellent machinist who also builds and drives sprint cars.

I hope you enjoy the pics. I will post more pics showing the removal of the carbon at a later date.

Big AL from Virginia
84 928S euro twin distributor monster

PS: the large reliefs in the piston heads remains a mystery. This car was #1411 built. Which is outside the first 500 receiving the previous model years pistons.