Piston differance
Melting Slicks
Joined: Jan 2007
Posts: 2,842
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From: Pasco Florida
Offset pins reduce piston slap. Most cast pistons have offset pins but many high performance pistons have on center pins.
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Last edited by MikeM; Jul 9, 2018 at 06:46 PM.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
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From: Pasco Florida
Burning Brakes
Joined: Aug 2013
Posts: 1,071
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From: palm springs ca
Used to be only 2 valve reliefs on the SB pistons and a F on each piston. Those days are gone.
ALSO all SB pistons weighed the same, dish, flat top, and domed! Won lots of bets on that. Also were the BB pistons back then. Cranks were balanced for all pistons used. I think it was 602 grams.
Now piston sets are within 50 grams of factory.
Boy at speed shop says that lighter pistons are high perf. He had to be a great grandson of the old mechanics
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Seems I remember the early 283 domed FI pistons weighed more than the the flat top pistons and therefore, there was a special crank released in service to account for the weight difference? Or, it could have been the '61 forged FI pistons that had the huge dome on them. Don't remember.
I think 265 and/or early 283 flat tops had only two valve reliefs. Don't remember. Been too long ago. Memory is a terrible thing to lose.
Your thoughts?
PS. I also know that I replaced one piston in my 260/350 Mercruiser engine with a TRW replacement and the replacement was much heavier than the OEM Mercruiser. Right on top of July 4th weekend so no time to balance the piston and in it went.
Last edited by MikeM; Jul 9, 2018 at 08:40 PM.
Burning Brakes
Joined: Aug 2013
Posts: 1,071
Likes: 322
From: palm springs ca
Mike,
Back in the days of old I had every SB engine and parts in the shop. Still have 265's and 283's + a bunch of 327's, not to mention some BB 396,427,and 454's. The 350's don't count much in the shop because they are a dime a dozen with exception to the forged cranks. I have a gram scale and weighed rods, pistons, and pins. In the last 30 years when I bought piston sets they were all over the place. The sets (8) were all the same but the heavy sets meant BALANCE shop. On the ones that were lighter than stock, I loaded the wrist pin with weight that I pressed into the hole, worked great, AND on my Mercruiser also.
I have to check weights on all the aircraft engines I rebuild. Nothing required there because the cranks are O. what ever yoy put on one side of the journal has to match the other! Can have 3 different opposing weight sets as long as each weight set is on the same crank journal.
Dom
Back in the days of old I had every SB engine and parts in the shop. Still have 265's and 283's + a bunch of 327's, not to mention some BB 396,427,and 454's. The 350's don't count much in the shop because they are a dime a dozen with exception to the forged cranks. I have a gram scale and weighed rods, pistons, and pins. In the last 30 years when I bought piston sets they were all over the place. The sets (8) were all the same but the heavy sets meant BALANCE shop. On the ones that were lighter than stock, I loaded the wrist pin with weight that I pressed into the hole, worked great, AND on my Mercruiser also.
I have to check weights on all the aircraft engines I rebuild. Nothing required there because the cranks are O. what ever yoy put on one side of the journal has to match the other! Can have 3 different opposing weight sets as long as each weight set is on the same crank journal.
Dom
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
Suppliers like TRW and others provided pre-machined pistons to GM for Service, individually and in packs of (8), all machined to the same size. In Service, the bore diameters were honed to match the purchased finished pistons.
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Le Mans Master
Joined: Feb 2008
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From: Folsom CA
Thanks John, your knowledge always amazes me.
The offset pins were used on many engine designs as stated to help reduce piston slap.
I knew Drag racers in the Stock NHRA classes that reversed the pistons and ran the offset pin on the inside rather than the outside of the bore. They claimed the engines would RPM better set up this way.
I never saw any engineering to support that thought but the guys I knew playing that game were winning and had class records. A, B and C Stock running Dodge engines.
Mark
The offset pins were used on many engine designs as stated to help reduce piston slap.
I knew Drag racers in the Stock NHRA classes that reversed the pistons and ran the offset pin on the inside rather than the outside of the bore. They claimed the engines would RPM better set up this way.
I never saw any engineering to support that thought but the guys I knew playing that game were winning and had class records. A, B and C Stock running Dodge engines.
Mark
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
I think I posted this before, but here's an article I wrote about ten years ago on the complete Flint V-8 process for "castings in - engines out at 300 per hour); with luck, the uploader will accept it. If not, PM me with your e-mail address and I'll e-mail it to you.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
Thanks John. Very interesting. I've never been to the Flint engine plant.
Racer
Joined: Oct 2012
Posts: 368
Likes: 48
From: Holland Ohio
Corvette engine dressout article.
Your engine build article uploaded great for me.
Do you still have the next file on the Corvette Plant engine dress out that you mentioned in the last sentence of the article? I would love to have that if available. Please post or send to me through PM.
Thanks,
Dennis
Last edited by PattiR; Jul 10, 2018 at 10:05 PM. Reason: email put on in error
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
JohnZ ,
Your engine build article uploaded great for me.
Do you still have the next file on the Corvette Plant engine dress out that you mentioned in the last sentence of the article? I would love to have that if available. Please post or send to me through PM.
Thanks,
Dennis
Your engine build article uploaded great for me.
Do you still have the next file on the Corvette Plant engine dress out that you mentioned in the last sentence of the article? I would love to have that if available. Please post or send to me through PM.
Thanks,
Dennis
Team Owner
Joined: Feb 2003
Posts: 54,024
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From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
John do you have a master list of all your articles on line anywhere. I know there are a few on the CRG. Would you mind if I get a friend of mine to put them on his Chevelle stuff.net web site The ones that pertains to both? They are great reads and would be great to help others