95 XP top end rebuild

[fyrman413]

Can anyone give me some help on a top end rebuild. The main question that I have is what size replacement pistons I should get. The cylinders are pretty well shot so I'll have to get them machined anyways...so should I go to a larger size or stay at OEM. It doesn't look like it has been rebuilt before, but I'm not sure. Also, what is a good brand of pistons for everyday normal use. I have a 95' XP so I'm working with a 717 engine. Any help would be great. Chris

[john zigler]

Re: 95 XP top end rebuild

you will need to clean the tops of your pistons, and look if there is any oversize numbers stamped on them. if not, they are std size, and you could probably get away with going to 1st over. (it is hard to say with out seeing / measuring the bore of your cyls). you can get all the parts you need from SBT right here. pistons, rings, bearings, pins, clips, gaskets ect. good luck with your doo. zig

[Bill O'Neal1]

Re: 95 XP top end rebuild

"Pretty well shot", With that description, I'd definately talk to whoever is going to bore the clyinders for you and get an opinion on what size pistons to buy. 1st oversized is only .010 oversized. That means any scratch in the clyinder wall exceeding .005 will not get machined out.

Typically, if in doubt, order pistons at least .050 oversized, or you will be sending the pistons back to exchange for larger pistons.

Buy cast pistons from SBT or Pro-X, as they will save you a few dollars and be very good pistons that last a long time. Avoid any racing forged pistons unless you are buildng a racing motor.

[Dan99XPL]

Re: 95 XP top end rebuild

Bill,
I'm curious why you said to stay away from forged pistons unless building a race motor? Aren't the forged pistons a tougher more dependable option? I was led to believe forged pistons are the way to go...

[frankey01]

Re: 95 XP top end rebuild

Forged products unless heat treated are normally weaker than cast products due to the type of process they go through to be made. Cast products are completely melted metal or steel and poured into the cast and formed and so forth as with forged they are heated up to be able to forge them in large hammers and therefore the molecular structure is not completely broke down therby weakening the structure of the steel or metal

[Bustoff]

Re: 95 XP top end rebuild

I was told that the forging process produces a heavier piston,and that cast pieces was somewhat lighter due to the casting process.

[1fastski.com]

Re: 95 XP top end rebuild

SBT now has the cyl exchange program , you can get pistons and cyls ready to go with no guess work :-)

[Bill O'Neal1]

Re: 95 XP top end rebuild

Wow! those are some weird ideas about forgings and castings...........

Actually, a piston can be made to be as heavy or lite as you want it, the process does not detirmine the weight.

If you look at a forged watercraft piston, you will notice it is forged to shape it, then mostly machined to size it properly. To make it light, they just machine more material off of the forging.

This is one reason why I do not like them in a normal watercraft motor rebuild. They are too light.

More importantly though is that forged pistons typically need a couple extra thousandths of clearance, which makes them rattle when the engine is cold. Forged pistons tend to expand slower than cast pistons and take more warm up time.

Cast pistons have more silicone in the alloy and are less likely to sieze in the clyinders and they expand at a more even rate, helping to control siezure problems and they don't scuff as easily.

Can you build a good motor with either type piston? Yes, of course you can.

Most rebuilders and oem's pefer cast pistons in engines that are expected to last years, not days ( in running time).