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By lowrider - 14 Years Ago
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Anyone recognize this Jahns piston? It has "Jahns" and "979" cast into the bottom near the pin boss. Label was missing from the box and someone wrote #1682 on the top. Looking to find out what compression or anything else about it.
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By John Mummert - 14 Years Ago
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I would guess that dome is about 5-6cc. Around .5 gain in compression ratio. I have seen Jahns with larger dome. What is the bore size? Many of the old Jahns pistons were 3.875". They will measure 3.868" to 3.869". Those things needed lots of cylinder clearance.
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By mctim64 - 14 Years Ago
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Never was too impressed with Jahns pistons, they seem cast kind of sloppy and any "set" that I've had to balance has been way off. On the other hand I do have a set running in my MGB that is still going after nearly 30 years of on and off use. Of course one failed in my first engine build and destroyed my block but Jahns sent me another to complete my set and I did the second block with them.  What can I say I was in High School. 
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By aussiebill - 14 Years Ago
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mctim64 (2/14/2011)
Never was too impressed with Jahns pistons, they seem cast kind of sloppy and any "set" that I've had to balance has been way off. On the other hand I do have a set running in my MGB that is still going after nearly 30 years of on and off use. Of course one failed in my first engine build and destroyed my block but Jahns sent me another to complete my set and I did the second block with them. What can I say I was in High School.
Tim, that block looks like 1275cc + 500cc, lol.
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By lowrider - 14 Years Ago
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John Mummert (2/14/2011)
I would guess that dome is about 5-6cc. Around .5 gain in compression ratio. I have seen Jahns with larger dome. What is the bore size? Many of the old Jahns pistons were 3.875". They will measure 3.868" to 3.869". Those things needed lots of cylinder clearance. They are supposed to be std 292. Box is marked 3 3/4 so I guess they are std bore 292. Rings I got with them are marked 292.
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By John Mummert - 14 Years Ago
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Dan, you might as well use them. You should be able to bore a 272 to std 292. Yeah, they're not the finest pistons ever made but you're not trying to qualify for the 500 either.
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By lowrider - 14 Years Ago
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Yea John. I've already picked up a complete 272 (with some good parts also, G heads, 1.5 rockers) to start. I dont plan to race it, I just use the car for cuisin' & shows. My plan is to build it over the next year and install it next spring. Shpuld keep me out of trouble.
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By yalincoln - 14 Years Ago
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check the wrist pin dia. to see if they are even for a ford, .912, if they are over size, they'll be stamped on the top. you'll still have to mic them to see if they are 272, 292, or 312. i've also got 3.935, std 341 linc. with the same comp. height. if you don't have a mic. take them to a parts store, they can do it for you. good luck, whatever they are.
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