5hp piston project?

[Thepaetsguy]

I am waiting for a $18 65.5mm piston with a 13mm wrist pin from a china shipper. Claims piston height is 48.5mm 65.5mm bore 13mm pin VERY CLOSE to a stock 5hp piston.

The stock 5hp wrist pin reads 12.4 I have very carefully opened it up to 12.8 and intend to polish it the final 2mm to fit the intended China pistons 13mm wrist pin.

NOW MY LAST HURDLE the .5 overbore am I nuts to think I can hone .5-.8mm out of a 65mm aluminum bore?? I have a block that is a .5 over candidate. I don’t fear going at a junk bore with an AGGRESIVE hone.

 

[EricD..]

You could probably hone it to that. Obviously wont be as true as if it were bored. But why do this. There is aftermarket high compression pistons available for the 5hp Briggs. That was/ is a popular kart engine

 

[Thepaetsguy]

You could probably hone it to that. Obviously wont be as true as if it were bored. But why do this. There is aftermarket high compression pistons available for the 5hp Briggs. That was/ is a popular kart engine

I have a few standard bores for longer rods. I don’t think anyone is going to have a boxed up cheap standard bore wiseco just laying around from the 90’s.

I really just noticed this piston was close for a stock billet/non billet 3.875 rod and wondered if i could pakastani machine it to fit.

 

[Minimichael]

Does it share the same wrist pin to piston top dimension?

 

[Thepaetsguy]

Does it share the same wrist pin to piston top dimension?

doh! stock reads 24mm and the eBay reads 17.5mm so 6 1/2mm in the hole. Well I have a couple long Horstman rods. I can sacrifice one for fun. Might still have a chance.

 

[Thepaetsguy]

This is going way left field but I had a 327 with a 283 crank and stock pistons that I think set them .250 down in the holes and they had been running it like that. I wondered if having that HUGE chamber would be good for the smog pump.

 

[sparkwizard]

You need to pump a whole lot of air to compensate for 5:1 compression.
I still have a 327 with a 283 crank with 6 inch rods. Had to use 350 pistons.
(Home made 302 Chevy)
Stock rods would have put them 1/8 inch in the holes, not 1/4.

 

[sparkwizard]

Are you stroking a 4 horse or destroking a 5 horse?
What is your goal here?

 

[Thepaetsguy]

Are you stroking a 4 horse or destroking a 5 horse?
What is your goal here?

I never checked the height from wrist pin to piston top. I am working with a worn 5hp block. Until MiniMichael mention that I was assuming it was the same.

I have a 2 Horstman 4.5 length rods for wiseco pistons. I can mill one out to see if it pushes the piston back up to the top of the bore.

I guess the end goal was to get a very worn 5hp back running with blatant disregard for machine work. I have boxes and boxes of 5hp parts so a junk block and an $18 piston is no loss.

 

[Thepaetsguy]

Wonder how much I can mill off the top of that piston before it gets thin? Hmm Ya that could work.

 

[Thepaetsguy]

I‘d be milling 7mm off the top with the Horstman rod. I can mill off as much as I feel comfortable and run some pop up. Edit: That isn’t gonna work either.

 

[sparkwizard]

Yikes! That looks like an inch!

 

[125ccCrazy]

Wonder how much I can mill off the top of that piston before it gets thin? Hmm Ya that could work. View attachment 319277

Your not going to have that much to mill off the piston... I'd go over to Bob's Karting forum and put a want ad for a piston..

 

[Thepaetsguy]

Your not going to have that much to mill off the piston... I'd go over to Bob's Karting forum and put a want ad for a piston..

This is simply to see if I can make one fit. I enjoy building and tinkering more then I do actually running these engines. I guess it’s like the ship in a bottle effect.. A lot of work on to the next.