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Jahn's Pistons

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Spridget64SC

Jedi Trainee
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Continuing the Jahn's Piston discussions from TulsaFred's Topic

Rut:

I took a quick look at the Jahn's I had at the shop last night. Did not inspect close enough to see a Casting number inside the piston (still on rods). But, the ring grooves were a nice neat 0.064/0.064/0.126 inch. The top of the piston has the "cresent moon" shape to fit into the combustion chamber to raise compression. Did not check skirt OD. Will look for the casting number and measure tonight.

Every time I see your numbers for the compression rings, I can't fathom what was going through the PO's mind. Maybe some kind of rather exotic repair????? But, after all said and done, I think your ability to use those pistons, on the cheap, is gone.

Take care,
Mike Miller
 
Spridget64SC said:
Continuing the Jahn's Piston discussions from TulsaFred's Topic

<some reverent snippage>

Every time I see your numbers for the compression rings, I can't fathom what was going through the PO's mind. Maybe some kind of rather exotic repair????? But, after all said and done, I think your ability to use those pistons, on the cheap, is gone.

Take care,
Mike Miller
Click to expand...

Gotta agree. A pistons/rings replacement is in the cards.
 
Mike,
Thanks for moving this to a different thread. I've contacted Hastings regarding rings and gave them all the measurements. I hope to hear back soon, but I'm not too hopeful after I read your comments. This engine is an attempt for me to learn how to put one together and I keep toying with the idea. I may be better served by buying another 1275 and going from there. However, this whole situation intrigues me and I want to find out why these pistons are the way they are. They have the 'horseshoe' domed top and they look really good. Upon closer inspection, number 1 has a shiny valve mark on the dome that is barely visible. The rods are attached and they look like the've been glass beaded or 'shot peened'. Nothing else on the engine has been cut down, original deck, original head surface, or modified, etc. When I hear back from Hastings I'll post here. If anyone else has advice on where to go to find out more please post. Any advice or thoughts are very welcome.
Thanks all, Rut
 
Star,
I've contacted the tech support people at Total Seal and given them the specs and I'll let you know what I find out. I had a difficult time finding the info I needed on their website, but that's probably just me.
Thanks, Rut
 
The Jahn's in the box at the shop have a 2.516" OD at the base of the skirt. There is no casting number inside the piston that I could find. There is a nicely cast "Jahn's on the underside of the crown.

These too have evident of past interaction with a valve and maybe even a light "meeting" with the cylinder head from a lost bearing. The pistons are on rods and the big ends show evidence of being resized.

FWIW, Total Seal rings are most likely not made in house by TS. TS buys bulk from other ring companies for whatever the application and then modifies the Top or Second ring to use their special sealing ring. Usually can decifer the ring source by the "coding" in the part number.

I remove the #2 rings from the 21253 pistons I use in the LPHP engines and from the replacement ring sets and send out to TS for machining to accept the "seal ring". Typically a setup charge and then a cutting fee per ring. Just have to tell them the finished bore size and turn around is about 3 weeks.

Not sure how small TS can go, but pretty sure its about 1mm. I've had them cut 0.047 rings up to 0.0625 rings. The 21253 rings are 0.059 (1.5mm) thick. So, there really isn't a set thickness for the TS ring package except for how "thin" can the core ring be to hold the special TS sealing ring.

I've got no future plans for the Jahn's, so first refusal to Rut and then anyone else for these pistons and rods. I just would like them to go somewhere to be used. $50 plus S&H. PM me if you want them.

Mike Miller
 
Mike, you have a pm.
Thanks, Rut
 
""""""But, the ring grooves were a nice neat 0.064/0.064/0.126 inch.""""""

so I guess the problem is finding rings?

Hastings;

2.780 plus any overbore
all their sets are .062 x8 and 5/32 x 4 that they list.....but you have to buy the oil rings separately. U can use a 501 oil set (4) plus .060 to get a 2.780 +.060
and their is other 1/8 oils that they have that might work depending on the finish bore. U have to look in their Catalog section "Ring and Size Type- Diametrical Index"

HEY Mike.........I didnt know it was you but for the Location :Walhalla
We got together in Vegas some years back......so HI. I havent been on this board in a ton........trying to get rid of more Spridget crap as I sold the car and have a FF now. Jerry B.
 
Jerry,
I found a couple of sources for the rings, but groove depth may be an issue. This is the original 948 engine for my bugeye and I'm leaning toward another 1275 instead of putting money into this one. My pistons are just a little small as well, so...

I just hate having an incomplete engine on a stand and not doing anything with it. It should probably go back in the box I took it out of so I won't be forced to look at it.
Thanks, Rut
 
Yep Jerry, It is still me. And still "Spridget-Crazy" after all these years. Still racing in SCCA too.

The pistons I'm referring to are some old Jahn's pop-ups for a 948. They have a "cresent" moon shape pop-up on the top of the piston. They measured out at 2.516" on the bottom of the skirt, and with the ring widths listed, a 5990+40 set would work nicely. They would make a nice period correct vintage engine with a 12A185 head and a 9CG block.

Take care,
Mike
 
Mike....

oh...a 948....was thinking big motor.

yeah 5990+40 would be 2.518 and a bit of file fit if needed.
Some one abve said the cr will be too hi with the dome but thats a easy fix on
the lathe or trimming a chamber a few cc's.

Glad too see that they dont have thew 1275 syndrome for a driver.

You take care.....PS ...Hap set up the new owner of my car to use Gary Johnson to do a fresh race motor and arrive and drive. The owner is in Puerto Rico and he flies over....nice!
 
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