74" Stroker Pistons
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From: punxsutawney
74" Stroker Pistons
Ok....So I messed up. Gathered up a bunch of parts I've collected over the years to build a shovel for a current project and I ran into a problem. a few months ago I had the cases and lower end machined and cleaned up. my flywheels were marked 23945-78 and 23923-78, I swear I measured them as the 3-31/32 stroke flywheels and read online that could be correct. (mistake #1) then I came across a really nice set of dual plug 74" heads and jugs. Took them to the machine shop and had them cleaned, decked and honed 30 over last month. (mistake #2)
I've had everything sitting on my bench for a while now. Put the lower end together last week and was excited to finally finish putting the rest of the engine together yesterday.....well...I got cylinder 1 on and when she hit BDC she stopped....****.... Pistons are hitting the flywheels. Took the pistons back off and milled them down about a 1/8 in or more, put back together...still hit....I could go more but I figured I'd post on here first.
Now I've read all over different forms that making a 74" stroker with an 80" lower and 74" jugs isn't unheard of and that a few people make pistons to do so. Well I call BS because the only pistons I can find anywhere are dang near $400 S&S ones.
https://www.sscycle.com/products/for...inch-oversize/
Now I love S&S in the right time and place but I'm trying to build a bare bones, nothing fancy, just runs shovel. I'm not about to put $400 into another set of pistons. I hate to pull the bottom end apart at this point though. but for $400 I'd get different flywheels.
My questions to the masses are.... 1. Does anybody else out there make 3 7/16 stroker pistons? for a reasonable price? Keith black makes stroker pistons for under $200 but not for 3 7/16 (that I can find)
2. If I'm able to machine down the skirts enough can I run 74" regular pistons on 80" rods? I've read that the stroker pistons have the wrist pin location raised, so would that just make the compression higher if I used stock pistons with shorter skirts? maybe 9:1 or 10:1? I'm hoping someone has experience in this realm.
I've had everything sitting on my bench for a while now. Put the lower end together last week and was excited to finally finish putting the rest of the engine together yesterday.....well...I got cylinder 1 on and when she hit BDC she stopped....****.... Pistons are hitting the flywheels. Took the pistons back off and milled them down about a 1/8 in or more, put back together...still hit....I could go more but I figured I'd post on here first.
Now I've read all over different forms that making a 74" stroker with an 80" lower and 74" jugs isn't unheard of and that a few people make pistons to do so. Well I call BS because the only pistons I can find anywhere are dang near $400 S&S ones.
https://www.sscycle.com/products/for...inch-oversize/
Now I love S&S in the right time and place but I'm trying to build a bare bones, nothing fancy, just runs shovel. I'm not about to put $400 into another set of pistons. I hate to pull the bottom end apart at this point though. but for $400 I'd get different flywheels.
My questions to the masses are.... 1. Does anybody else out there make 3 7/16 stroker pistons? for a reasonable price? Keith black makes stroker pistons for under $200 but not for 3 7/16 (that I can find)
2. If I'm able to machine down the skirts enough can I run 74" regular pistons on 80" rods? I've read that the stroker pistons have the wrist pin location raised, so would that just make the compression higher if I used stock pistons with shorter skirts? maybe 9:1 or 10:1? I'm hoping someone has experience in this realm.
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From: Niles Canyon Ca.
You sure you have the right pistons and are installing them correctly ? Sounds like the clearance cutout on the piston skirt is either not there or in backwards which will allow the pistons to hit each other when going bdc.
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From: punxsutawney
The pistons arent hitting each other, well they may, but theyre for sure hitting the flywheels. Ive only had one side on and it hits. I tried both pistons and both directions and they hit. Even the one with the skirts cut down hits....☹️
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From: la la land jerzey
picture up what your looking at including any piston numbers like 2900 series S&S - maybe 2800 S&S but S&S has dropped most of the shovel stroker pistons in favor of a fits all -- what happens is the compression changes depending on stroke as the piston no longer comes up to the top of the bore -- so shorter then 4 3/4 and that has the most compression at 9 3/4 to 1 by the time you get to 4 1/2 stroke its 7 1/2 to 1 and no the others no longer exist
measure the compression height < center of the wrist pin to the top of the piston out side edge not to include the dome that is a different calculation
also as you not having the special tolling needed for that from the top edge of the wrist pin hole in the piston to the top of the piston BUT I need to know if its a .791 or ,792 pin diameter wrist pin = everything is being blended today evo rods in a shovel then -- even worn shovel rods are used and they are touch honed to fit the bigger evo pin kind of thing
measure the compression height < center of the wrist pin to the top of the piston out side edge not to include the dome that is a different calculation
also as you not having the special tolling needed for that from the top edge of the wrist pin hole in the piston to the top of the piston BUT I need to know if its a .791 or ,792 pin diameter wrist pin = everything is being blended today evo rods in a shovel then -- even worn shovel rods are used and they are touch honed to fit the bigger evo pin kind of thing
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From: punxsutawney
Johnjzjz, Is your first paragraph in reference to the S&S piston compression or the stock? If that's how low I would get with S&S pistons then I'm really screwed with the stock ones 
I gave the pistons to my buddy to mill the skirts down further for me so I can't measure them today, but I can measure the wrist pins when I get home from work. I'm 99% sure they're standard shovel and not evo but I'll check.
I gave the pistons to my buddy to mill the skirts down further for me so I can't measure them today, but I can measure the wrist pins when I get home from work. I'm 99% sure they're standard shovel and not evo but I'll check.
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From: la la land jerzey
stock pistons are cam ground - what does that mean - it means the location used to measure is standardized at the bottom of the piston - when using a mike you find the largest diameter at the bottom 90 degrees from the wrist pin - and that is used to set the piston to wall clearance - by removing the material from the bottom you will create a noise called piston clatter - as the standard numbers used to set the piston should be .002 to .0035 - when you done guessing at this you may end up with .006 to .010 piston to wall or even more - the piston ring flutter with be so pronounced that it will sound like a cement mixer with an extra amount of stone
my guess you do not have the tooling to configure this correctly - SO - perhaps you might want to consult a engine shop that actually does this not some one with a lathe
my guess you do not have the tooling to configure this correctly - SO - perhaps you might want to consult a engine shop that actually does this not some one with a lathe
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From: punxsutawney
It is going to an engine machine shop, ha ha I wasn't having someone fly by night do it. It's nice to have friends in the right places lol. The question still remains though, will the pistons even work compression wise? or am I going to be at like 5 to 1. Or will those S&S ones even work, they list a stroke of 4.5, standard 80" is 4.25.
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From: la la land jerzey
and this ( engine shop ) did not mention the machining location was not the best of ideas to remove material from
I would suggest you try another that one is missing the real world concepts
and ( BTW ) I am not in a pissing contest with you - I was pointing out you have stupid people helping you - the end result will be your engine if going to trash out
in a small way I was trying to alert you of that - but the haha tells me alI need to know -- good luck in your adventure
I would suggest you try another that one is missing the real world concepts
and ( BTW ) I am not in a pissing contest with you - I was pointing out you have stupid people helping you - the end result will be your engine if going to trash out
in a small way I was trying to alert you of that - but the haha tells me alI need to know -- good luck in your adventure