Jahns Pistons Questions

Discussion in 'Street/strip 400/430/455' started by Brent, Jun 30, 2022.

  1. Bens99gtp

    Bens99gtp Well-Known Member

    This block was only 4.350 bore. Just a standard 464.......there also was detonation.....the piston is perfect smooth as new..........the picture does look like it but its just the reflection from the led lights above that makes it look peppered.

    These were brand new, and finishline did the install, so how much they were stretched to and what lube they used and how many times they were torqued I cant answer.

    Tom said bearing clearance issue.......which clearly it got hot and ate things hence the burn marks on the crank and rods.

    Now with my lower quality measurement tools what I checked seemed within a few .000x numbers as what I was told the clearances were set to. And I have a set of mains and 6 rod bearing that look brand new not even worn through the coating minus a few scratches from the trash that passed through at the end of its life. Now could that journal had been clearanced wrong, maybe. But I will going to assume that if any machinist got the other 3 right.....they got the 4th right.

    Now I had the filter off and apart just 2 passes b4 death and there was no signs of any debris in the filter.......and the 1st pass that day ran within a few thousands of what my weather station predicted.......so again assuming not to much was wrong there. But that pass was 1 of just a few handful of passes that were 1/4 mile and it was going through at almost 7000 rpm.

    So its seems like to this untrained individual that since I had no sign of bearing material b4 that 1/4 pass, and it pukedthe pass after, that whatever went wrong did on that pass.......and if that bolt stretched on that pass it would cause the bearing clearance issue which over heated the rod causing the major damage.

    I didn't push the issue with molnar any farther, because even if it was a product failure its not like anyone would step up and say....yep my stuff failed let me fix the damage it caused.

    Everyone has someone else to blameand I'm stuck on the end paying. So if no one was going to step up why push the issue..........it wouldn't do anything beside make me more disappointed.

    From my experiences in life often the simplest explanation makes the most sense and possibility......to me that is the damaged happened on that pass from a bolt failure and from there it got hot and broke big time.

    sean Buick 76 likes this.
  2. No Lift

    No Lift Platinum Level Contributor

    I had a set of those Jahns pistons back in the early 80's set up for 11:1. They are what Jahns called their "Cast Racing" pistons. Noticeably heavier than stock but built like a brick s---house. They worked great in my 65 running low 12's, shift around 5500. Then I decided Nitrous was needed. They worked for a while after that.
  3. Jim Weise

    Jim Weise EFI/DIS 482


    I had exactly the same failure about 33 years ago. Brand new 464, all the good stuff, this was my first big time race motor for the car we were racing.. Crower billet rods.. girdle, custom oil pan, ported heads ect ect.

    It dynoed out fine, no sign of issues.. on the 4th pass, it spit out number 7 rod right off the starting line. The oil filter was not packed with rod bearing, every time we cut it, which was twice.. once after the intial break in, and once after it was dynoed.

    Looked exactly like what you have there.. the rest of the engine Looked perfect, it actually still had oil pressure before I shut it off. The only evidence that anything was wrong was the block with a hole in it, and the con rod we picked up off the track. One rod in a thousand dollar set.. :eek:

    But there is no question that failure started with oil starvation.. a billet rod did not break in half.. It caught that bearing from day one, the motor was down in power on the dyno, but having no frame of reference, (it was the first motor I ever had on a dyno back in 1990) we had no idea. Made great torque, but caught that rod bearing, which limited high rpm output. Made 570 Torque, but only 540 HP, and it dropped off hard just after the torque peak. We blamed that on the iron cylinder heads, which were part of it, but in the ensuing years, and hundreds of dyno sessions since then, I have come to believe that motor was hurt from the very first dyno pull.

    To this day, I don't know for certain what happened to that engine. The most reasonable explanation is that there was debris that found it's way into the crank, or was in the crank, and it blocked oil flow to that rod. I did build it.. I knew every bolt stretch number and every clearance down to the tenth. There was nothing I could identify as a cause for just that rod bearing burning up.

    I understand wanting to blame a product, because I can't find any other cause. The real evidence disappeared when that rod burned up, causing the piston hit the deck, which bent the rod, and broke the cylinder.. The next time the crank spun it caught the rod on the way down, and pulled the cap off of it, the next cycle back up, it caught the now free swinging rod again, and bent it and then broke the rod in the beam, and spit it out the side of the block.

    This is almost certainly the cause/sequence of events in your engine failure. Had the rod bolt broken, as you contend, then rapid chaotic disassembly occurs instantly.. and that rod bearing ran for a least several passes with no oil, to burn it up like that.

    That is my professional opinion, one shared by every one of my peers that I showed your pictures to on the private machinist/engine builders forum I am part of on facebook.

    They had pictures of rod breakage.. and in every case, the bearing on the broken rod, was all beat up, but it was not burnt up.

  4. Bens99gtp

    Bens99gtp Well-Known Member

    That is all possible, this motor never did perform to level that Bobb thought it should....spilled milk now. Moving on to try again
  5. Jim Weise

    Jim Weise EFI/DIS 482

    good luck with it Ben.. :cool:
  6. Bens99gtp

    Bens99gtp Well-Known Member

    I hope so dan zepnick hooked me up with solid fill 464 with crower rods. His short block went 10.0s and only has 4 passes on it, I had my heads gone through at Francis...only had a slight buffing in 1 chamber and 1 exhaust valve to replace.....from the flow sheet I have my heads flow better than what Dan's do so hopefully we have a setup to run low 10s high 9s. With any luck I will know by the end of year......having a real race transmission built.......not a warmed over stk unit build by a fat hillbilly who only thinks he knows what he is doing......but I knew sooner or later I would need one built by a true professional
    sean Buick 76 likes this.
  7. Bens99gtp

    Bens99gtp Well-Known Member

    Back to the orginal cast piston this was originally about
  8. Pro69GS400

    Pro69GS400 Well-Known Member

    I’ve had these Juan’s Pistons for a while. There 20 over 400. Still in the original package. Definitely different than what the original poster has. They were purchased from Kenne Bell with a 1970 date post mark.
    . BA12E9F6-0346-441A-B62B-FA3C4F1E34E4.jpeg 8BF13270-5A18-48BA-A08F-166B76EE1AED.jpeg B65DC419-7168-4AFE-BE4C-1B59014C75DB.jpeg 83A69A9E-3F47-4B77-B66C-34BA1F9F9A54.jpeg 6251CFCF-2A35-4CC6-9201-281688FD48D2.jpeg 04FBC3BB-7DF5-4C4E-BA62-A05D3D2ED98B.jpeg
  9. hugger

    hugger Well-Known Member

    Damn that's ALOT of skirt!
  10. Jim Weise

    Jim Weise EFI/DIS 482

    Those are the Superlight forged versions like I had in the 430 I mentioned earlier.

  11. m louk

    m louk Well-Known Member

    The ones I bought back in 1970 20201125_102027.jpg
  12. Brent

    Brent Founders Club Member

    Interesting information gents, thanks. I did a lot of research as well and am pretty convinced these are the Jahns racing cast pistons. They must be very heavy, you can tell it took a lot to balance the motor. I finished taking it all apart and found a May 1985 date on the bearings, so it's an old build. I built my first 455 in 1988 when I was 17 in high school, damn I'm old too. Everything seems to be well done in the motor, except they used the stock rod bolts. Were ARP or other heavy duty rod bolts available in 1985? I know I didn't use any till about the mid 90's.
    PGSS likes this.
  13. Sport1

    Sport1 Gran Sport1

    I still have my Jahn's super light pistons that I purchased many years ago from Kenne-Bell. The pistons & center to center Buick connecting rods are still around. I also purchased the KB CSP (competition switch pitch Turbo 400 (67 model year) that I would like for Jim to convert it back to non-SP. My transmission has the long transmission oil filter. I connected the 2-speed solenoid wire to the brake light switch, however, the torque converter needed an overhaul to say the least. Earlier, I had purchased from KB the Rossi 11" non SP for my original GS Turbo 400 and it worked great. Presently, I only have the CSP 400 transmission. The real problem for me for many years was after purchasing the parts, there wasn't any Buick performance machine shops around, they only knew about chevy & ford. The really good cams were ground at Sig Erson, the Mark III & Mark IV cams were excellent. I ended up with the original KBMark 107 window rattler camshaft, mallory dual point distributor, Carter CS-4847 1000 cfm thermo-quad. That mark107 cam was the meanest & nastiest thing with the Doug Throley 1'7/8 headers, and the edelbrock B4B aluminum intake with the 4:30 rear gears proved quite impressive. As I stated earlier, the part breakage became a real problem. Now at this juncture of my life "I wanna be a tootsie roll - look good and last a long time" The time is now. As for Buick GS history, the former Sanford, NC - 1/4 mile drag strip recorded way back in 1970 the fastest elapsed time of not 13:38 @ 105 mph on the base Stage1 with no A/C and manual brakes. This 1970 GS Stage1 was fully equipped with A/C; PS/PB /full gauges/front bench seat with the shifter on the column. The rear gear set was the optional 3:91. This vehicle was special ordered from Al Smith Buick - Raleigh, NC. With little over the initial 1,000 mile oil change clocked a blistering 12:62 @ 109 mph. The car ran so fast that it was protested as being illegal. The car was in the lightest sense pure hell on the streets of Raleigh, NC. If there's any people left at the dealership, they would verify the Buick history that this car carried. Now, no pun intended, you think Lassiter's Ole Blue was fast, then think again. This dark Green/Green vinyl top GS 455 Stage1 had the Hemi boys & Chevelle 454 LS-6 boys running for the hills.
    m louk, Stage 2 iron and Mark Demko like this.
  14. BQUICK

    BQUICK Gold Level Contributor

    Not pure stock it didn't....especially an AC, PS car....
    PGSS likes this.
  15. Sport1

    Sport1 Gran Sport1

    This was when there was Sunoco 260 race gasoline. This vehicle was produced during the 3rd quarter production run late 1969 for the new 455 engine. The tooling for the new 455 blocks was very good prior to the 1969 Federal Clean air act which Buick decreased the static compression of the 455 engine by changing the thickness of the head gasket. The static compression was reduced to 10:1 down from 10.50:1. This vehicle also had the special BB Turbo 400 transmission that included the L-88 Torque converter (which is pure stock GM part number). This along with the 3:91 rear gear ratio (later production runs removed the 3:91 rear gear option for A/C cars) really did make the car run into the 12 second bracket. This production vehicle was and will always be in the pure stock category, even with AC / PS / PB. Most of all, the owner "Gene Henson" knew how to race his car & he did it quite well. This vehicle was a NHRA record holder for many years in Pure Stock. This vehicle came from the first run of the 1970 model year of ( October /November 1969). There were a lot of changes during the 1970 model production run. Look at the history of the Reynolds Buick 1970 early production run of pure stock Jones / Benseik GS 455 Stage1. Also, the early production run engines sported a slightly different Stage1 camshaft as the camshafts were made at different parts vendors which included Mellings and Perfect Circle I believe. The only downside of this marvelous engine was the oil pressure issue > spun #7 rod bearing.
    PGSS likes this.
  16. PGSS

    PGSS Silver Level contributor

    This is new info...
    To me anyways...How is this just being brought up?
    Last edited: Aug 5, 2022
  17. PGSS

    PGSS Silver Level contributor

    Sorry for my ignorance but i'm still confused?
    The early produced 455 stage 1's had 1/2 point higher compression and a different maby hotter cam.
    The new from the factory Jones/Benseik car that was tested and did a 13.6 was maby one of them and not very "doctored"?
    Last edited: Aug 6, 2022
  18. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    PGSS likes this.
  19. PGSS

    PGSS Silver Level contributor

    Bigger dish on the 455 with more chamber CC but higher measured compression ratio..
    I guess the deck height on the 430 makes the difference?
    Is the SF motor the standard 455?
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


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