size of piston 1972 25hp. evinrude 25203r

[jethro66]

Hey guy's I have a question,I would like to rebore my cylinders on my motor and just wanted to know what size of piston and ring's do I need to get after a rebore? how much doe's a rebore cost?

 

[F_R]

Re: size of piston 1972 25hp. evinrude 25203r

First things first. First locate a shop that can do the job. They will quote you a price and look at your cylinders and tell you how much needs to be bored out. Then locate replacement pistons before doing the bore job. Just in case there is a problem getting what you need. The shop can fit the piston clearances to specs.

 

[jethro66]

Re: size of piston 1972 25hp. evinrude 25203r

Ok ,so they can be bigger piston's?

 

[Chinewalker]

Re: size of piston 1972 25hp. evinrude 25203r

Yes, you would get a piston that is slightly larger in diameter. However, you are looking for oversize pistons on a motor that hasn't been made in over 30 years. Try the long-established dealers first - they might have something tucked away in a dusty cabinet...

Around here, rebores generally run between $40 and $50 per hole...

- Scott

 

[F_R]

Re: size of piston 1972 25hp. evinrude 25203r

Ok ,so they can be bigger piston's?

Now I'm wondering if it really needs to be rebored. Why do yiou want to do it? Are the cylinders damaged? It is folly to rebore a motor that doesn't need it.

 

[Chinewalker]

Re: size of piston 1972 25hp. evinrude 25203r

I agree. If you're reboring thinking you'll get "BIGGER" pistons, it won't work. Bigger pistons do not give you more performance. Oversize pistons are balanced and cast to give as equal performance to original size as possible, as they are often replaced singularly, not necessarily as a set. Oversize pistsons are typically used when a ring lets go and scores the cylinder walls to the point where the only way to repair the damage is to bore the cylinder out. Also used when the cylinder is just plain worn out and is out of specified tolerances...
- Scott

 

[jethro66]

Re: size of piston 1972 25hp. evinrude 25203r

No, compression is 90 on the top and 115 on the bottom. figured I had a blown head gasket so I took it apart and inspected it ( blown with a teaspoon of water coming out0. I found 2 pot's on the cylinder wall and some pisaton damage and lot's of carbon deposit in the exaust housing.piston size is .030

 

[F_R]

Re: size of piston 1972 25hp. evinrude 25203r

It's already .030? Unless you can get it sleeved, it's good-by for that one. .030 was the largest oversize made for that year.

 

[iwombat]

Re: size of piston 1972 25hp. evinrude 25203r

Can your scored jug be honed mostly clean? A minor scratch or two after honing isn't the end of the world either. I think your real problem was the blown gasket. If the bores are in spec, I'd hone it button it all back up and see what kind of compression you can get. Worst case, you take it apart again and get it bored. Best case, you're back on the lake.

 

[iwombat]

Re: size of piston 1972 25hp. evinrude 25203r

How badly are the pistons scored? A few minor scratches - still usable. Looks like it's been dragged through gravel - not usable.