Need help identifying 98MM pistons

tomkirkcis · 10-14-2015, 07:21 PM

I am tearing down my 3.2SS. I purchased it used so I am seeing the inside for the first time. I need help identifying the pistons. It is a twin plug carb engine. The engine has 98 MM Mahle Nikasil cylinders. The pistons are a dome with fairly large valve reliefs. The compression rings are 1.5 and the oil ring is 4.0. Looking at them I beleive they are Mahle. Anyone know these? any idea on indicated Compression Ratio? Part number?

Thanks Tom

chris_seven · 10-15-2015, 02:27 AM

There was a 'wedge' piston made in Europe for Max Moritz and they were 98mm diameter.

They were manufactured as a high compression piston for use with K Jetronic and sold as complete sets of barrels, pistons, rings and pins.

Ring Packs were never offered as spare parts.

When I have seen them before ring sizes were 1.2, 1.2 and 3.0mm which is a real PITA.

If these pistons have different size rings they may be easier to find.

The forging number on the inside of the crown used for the Max Moritz pistons was 98P11.

jpnovak · 10-15-2015, 07:12 AM

These look like the Mahle Motorsports 98mm pistons. I have the same ones in my 3.2SS.

chris_seven · 10-15-2015, 07:46 AM

I thought that the US made Mahle Motorsport pistons were modelled on the German made Max Moritz pistons but had a different size ring pack.

I thought that the rings were 1.0mm x 1.0mm x 2.0mm and they couldn't supply rings for the original Max Moritz pistons when I contacted them recently.

Dou you know the ring sizes as it would be good to know?

KTL · 10-15-2015, 08:03 AM

I think they are Mahle Motorsports also. I had a Carrera set (23mm pin bore) in my half-a$$ed 3.2 short stroke that came in my racecar.

98mm Mahle Motorsport Pistons

Sorry to see that red goop on the cylinder spigots. That stuff hardens and is a pain in the butt to clean off.

jpnovak · 10-15-2015, 01:05 PM

Chris,

My pistons are originally 1.5, 1.5, 4.0mm rings. I had Total Seal make a custom set of rings since I could not find what I wanted off the shelf. Price was reasonable and fast turn around.

The MM pistons have an asymmetric dome similar to a wedge interpretation of a CIS pistons.

Tippy · 10-15-2015, 03:19 PM

I paid $250 for my 98mm TotalSeal rings from EBS.

tomkirkcis · 10-15-2015, 04:20 PM

Guys

Thanks for the quick response. I also appreciate the info on rings. Great to know. The car is in a state with 93 octane fuel readily available. The heads are twin plugged. My motor uses SC large port head castings. Any idea what compression ration that might yield with these pistons? I have never had a detonation issue. Wondering if I sit tight or get greedy and try to bump the compression a bit.

Tom

jpnovak · 10-16-2015, 04:21 AM

Mine CC'd at 10.12:1 on 78 SC heads with twinplug with 1mm deck height. They should not be more than 10.5:1.

If this is a street car I would not go any higher due to fuel quality. Of course, this could change based on the dynamic compression dictated by the cam choice. If you are running a wide-lobe center cam (S, GE60, other) that would match the pistons and carbs you could get away with a little more compression. The only way to really get more compression is to make major mechanical changes. I do not think that low deck-heights, shaved heads, etc are proper ways to increase compression. Besides, these assembly and machining techniques will only get a few tenths. Not really worth it.

Clean everything up, assemble properly, optimize fuel and timing for this engine and enjoy!

tomkirkcis · 10-16-2015, 09:07 AM

If it was just a reseal, I would just put it back together as is. The reason I am asking is I had a freak cam failure in this motor. The end lobe of the one of the GE60's in the motor snapped off the billet. I have had other projects that needed to finish before I could get back to this and the motor just sat. The recent teardown found no bent valves, or any sign of head or piston damage. I was very lucky.

snapped camshaft

I need to buy new cams so the question is do I just put GE60's back in or do I change the cam specs.

The motor ran great and was alot of fun before the cam failure. The motor is in a car I only take out for spirited runs. I am thinking the car is so light and already short geared, it might be more fun if I give up some torque for some more HP. I am thinking since I am buying cams anyway, I might go for more agressive cams

The induction is Weber 46's. PO seems to have had some serious head work done. I measured 42mm intake ports and 39.5 MM exhaust ports. I will be curious to see how those flow test. As long as the measured compression is over 10, I think retaining those pistons would be fine even with a more agressive cam.

Any thoughts?

Tom

jpnovak · 10-16-2015, 05:14 PM

I would not go for more cam unless you are doing all the supporting oil modifications to the bottom end to support the higher rpm required by the cams.

Specifically, cross drill the crank so you don't spin a rod bearing on #5 or #3 at rpm.

Steve@Rennsport · 10-16-2015, 05:41 PM

Quote:

Originally Posted by jpnovak

I would not go for more cam unless you are doing all the supporting oil modifications to the bottom end to support the higher rpm required by the cams.

Specifically, cross drill the crank so you don't spin a rod bearing on #5 or #3 at rpm.

Solid gold advice right there. There is a host of oiling mods to prevent bearing damage (and worse) to #2 & #5.

#3 is fine as that's closer to the ends.

tomkirkcis · 10-17-2015, 02:45 PM

I appreciate it. I haven't split the case yet. Maybe I will luck out and the PO did the oiling mods. If not, I will take your advice.

Tom

Henry Schmidt · Henry Schmidt's Garage

We can drill the crank, groove and coat the bearings in-house. This service generally has a 4 day turn around.
There is also a modification to the case that should be completed to utilize the full potential of the crank mod.

tomkirkcis · 05-27-2016, 03:56 AM

The pistons have been cleaned up somewhat looking for makrings. I see no casting marks under the dome. I did find a few markings on the crown. Could the experts look at these and tell me if these still are consistent with the pistons being Mahle and what the markings mean?

tomkirkcis · 05-27-2016, 03:57 AM

Steve@Rennsport · 05-27-2016, 06:15 AM

Perchance, did you measure the piston diameters (or bores)?

KTL · 05-27-2016, 07:22 AM

When somebody plunge-cut the underside of the piston crown, they removed the casting information. Nonetheless the casting numbers don't tell you specific size

The M on the crown with the numbers above and below is indeed a Mahle symbol. I don't know what the numbers indicate.

Take a look again at my pistons I sold 98mm Mahle Motorsport Pistons

Agreed with Steve (easy to do), just measure the skirts with a basic micrometer. Heck, even a cheap set of dial calipers is sufficient just to get a ballpark size.

tomkirkcis · 05-27-2016, 04:47 PM

The motor is a 3.2 SS. They are definitely 98mm. I bought the motor used and it came with some urban legend as to what had been done to it. With the casting numbers gone, I guess I have been obsessed with figuring out EXACTLY what they are and where they came from. Is it common to take that much material out from the underside the dome?

fred cook · fred cook's Garage

Quote:

Originally Posted by tomkirkcis

The motor is a 3.2 SS. They are definitely 98mm. I bought the motor used and it came with some urban legend as to what had been done to it. With the casting numbers gone, I guess I have been obsessed with figuring out EXACTLY what they are and where they came from. Is it common to take that much material out from the underside the dome?

That is way too much material just for balancing purposes. It was probably done to lighten the pistons as much as possible. You might give Don at EBS a call. I bet he can tell you all about those Mahle pistons! Good luck!