Use a table ban saw to hack off the 340 piston crown .

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mopowers said:
VERY nice gesture! I wouldn't waste your time. When his junk blows, you know who he'll blame...
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Ironracer said:
After actually doing some recalling in this thread I believe he was recommended to probably sell those and get the right Pistons I mean the creativity in the workarounds are pretty doggone redneck re-engineering science and I dig it, but man if you can get the stuff to work together the first time...
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Can 1wildrt do figuring with a 3.79" stroke crank? Instead of the 4" crank? What's th .135" look like then?
 
Jesse, what 340 pistons do you have/have access to? If you haven't read about what was referred to as the Hoover engine look here... 340 pistons in a 360?
Back in the 70's Tom Hoover use to use 8.5-1 340 pistons in 360's... Apparently you take .030 off the top, chamfer the edge & it may need valve reliefs cut depending on cam selection... There was also mention of possible having to relieve the back side of the pin boss to clear the crankshaft counterweights....

That's allot more involved that just a shave off the top... You probably would be hugely money ahead to track down a set of 360 pistons with a decent compression height...
 
Jessearent said:
Can 1wildrt do figuring with a 3.79" stroke crank? Instead of the 4" crank? What's th .135" look like then?
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No, YOU, the Assembly Man, have to blueprint and map the build. And I would not even ask someone to do that. That's about like Horseshoes and Hand Grenades brother. Cuz if you're off by a few thousands here and there you'll have a pile of horseshoes left after the hand grenade goes off in it
 
1WildRT said:
Jesse, what 340 pistons do you have/have access to? If you haven't read about what was referred to as the Hoover engine look here... 340 pistons in a 360?
Back in the 70's Tom Hoover use to use 8.5-1 340 pistons in 360's... Apparently you take .030 off the top, chamfer the edge & it may need valve reliefs cut depending on cam selection... There was also mention of possible having to relieve the back side of the pin boss to clear the crankshaft counterweights....

That's allot more involved that just a shave off the top... You probably would be hugely money ahead to track down a set of 360 pistons with a decent compression height...
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Don't have access to any 340 pistons, bummer.
 
You scared me with the .135" figure. Maybe I need the forged 3.79" crank. Price difference is bout $200. The way I figure, that leaves about .67" that needs to be dealt with. I am figuring just mill that goofy ring that's on top of the stock piston then use the appropriate gasket to put me home at tdc flush with the deck or "close" hallelujah.
 
Clearly I need to read this whole post, your thinking 3.79 or 4" stroke? What rod? The Hoover engine is based on a 3.58 stroke which has the bottom of the piston needing to be cut for clearance... A 3.79 stroke will pull the piston .105 deeper in the hole, that means the skirt needs to be shorter to clear the crankshaft.. A 4" crank needs the piston to be .210 shorter... Your gonna need the right pistons, not worth the risk, especially if your not already intimately familiar with all the possible problems...

Trust me, I get the redneck approach... It fits me just fine but I also know doing what you have in mind "On the cheap" still won't be cheap, but it's got the potential to be an expensive fail...
 
Jessearent said:
You scared me with the .135" figure. Maybe I need the forged 3.79" crank. Price difference is bout $200. The way I figure, that leaves about .67" that needs to be dealt with. I am figuring just mill that goofy ring that's on top of the stock piston then use the appropriate gasket to put me home at tdc flush with the deck or "close" hallelujah.
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You need to consider what's happening in the bottom of the engine.... If the piston is being pushed .200 higher then it's also pulled .200 lower, under the piston is the crankshaft.... You don't want those two things to meet....
 
Thanks for all your input 1wildrt . I am gonna playit "Safe" buy theshorter 3.79 forged crank nd bolt it all together. the take those measurements. I will be happy to share theresults ...til then my friend. LOL and God bless you for your giveing heart . Sincerely jj
 
Jessearent said:
What would the compression be around, if the pistons stuck out a little bit....like a stock 340....with 65cc chambers/ also with 70cc chambers. Any one brave a guess....4" stroke crank being used.
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That depends how well you clean up the swarf after cutting the size of the pistons down.
 
Ironracer said:
Weren't you gonna do a backyard Foundry?
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Only guys who want to break world speed records cast their own pistons...

cb79e375749b7751e76575126d360aae.jpg
 
famous bob said:
guys who chase world speed records , absolutly dont run cast pistons !!!
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Burt Munro did.

He made them himself in his home - a garden shelf.
He broke world records which still stand today.

 
I tried to find smeoone with bearings spacers, alas, to no avail. Maybe I gave up to early. But the 3.79" crank is on my wish list.
 
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