Recommendations on replacement pistons?

[Tim of DO THE TON]

I just tore open my 2500 mile old engine, and it looks like I beat the thing to death breaking it in. Bad scoring on the pistons/cylinders.

Might be recoverable, might not. Before I resign myself to going up another size and ordering another set of MikesXS pistons/rings (which these were - 0.5mm over bore) anyone have suggestions on better product for my money?

There are sets on eBay shipping out of Japan for $100 (total shipped) for the set of pistons/rings/pins/clips which is cheap, but then again, you get what you pay for. I'm betting these are the sets MikesXS sells for $150 or so for the pair.

I don't mind spending more money for better product.

These are going into a stock engine, with the XS1 camshaft degreed for a thinner copper head gasket. Nothing outrageous - did that with my 750 rephased engine.

 

[grizld1]

Tim, I've never pulled down an XS650 top end that didn't exhibit some scoring of bores and piston skirts, regardless of miles or provenance, but here's what I'd recommend. For wrist pins use Wiseco--they're significantly lighter than OE. Japanese OE replacement cast pistons should be fine for your application; the only aftermarket options are forged pistons sized from 77.5 mm. up, which are heavy and stronger than you need. The best bang for your buck in top end longevity is a silicon carbide treatment, available here: www.bore-tech.com

 

[Tim of DO THE TON]

Here are some pics. Looks like overheating perhaps. My first ride on the bike was likely quite lean (it was a cold March night and my pipes were glowing a bit ) - I was a little eager to ride after years of building.

Going to have them checked out before I go replacing everything. Honestly think they'll be fine cleaned up a bit and with fresh rings. Can't feel any wear on the pins - looks like they got overheated along with everything else.

 

[grizld1]

Tim, if I have one rule that I set myself, it's not to draw any firm conclusions from photos, so take what follows with a grain or more of salt. But if it were my 2500 mile motor, I'd be a bit concerned about the copper on the wrist pins (it used to live in the small ends of the rods) and the carbon buildup on the piston crowns and valve pockets. Scoring doesn't look too bad, but be sure to mike out those pistons closely for distortion.

 

[angus67]

i spotted that copper too. 2500 miles is not alot. something else is going on.
Judging by your screen name, I assume you like to throttle the throttle?
Do it right this time, and be patient. next time you might need a whole new motor.

 

[Tim of DO THE TON]

This was an engine I built 4 years ago, ran for 2 years and then pulled. I replaced it with a 750 (MikesXS) rephased ported head motor with oversize titanium valves.

I'm cleaning this engine up for my Voodoo Vintage MK4. I was taking it apart mainly to clean it, and replace the head which has 2 stripped tappet cover studs. I picked up a ported head / matching rocker cover from someone local and an XS1 cam with the 36t sprocket on it, degreed for use with a thinner copper gasket which came with the cam.

Anyhow - I likely didn't assemble this engine well lubed enough 4 years ago, and then it sat for probably more than a year before running it. Then I likely ran it too hard to start off with being eager to ride after working on the bike for 3 years.

The engine I just built last winter was more carefully assembled with nice Lucas assembly lube in all the right places, motor oil elsewhere, proper Threebond application etc. all by the books and then carefully broken in.

Of course I might have broken something in it in October down in Alabama, as I got it up to around 120 at 9000 RPM with the taller 5th gear from MikesXS

I'll check out the small ends of the rods. The bike was running rich when I pulled the engine. I think the pilots and mains in my VM34's were a tad big, and most of the riding the engine got was stop and go around town. Not many opportunities to wind the engine up.

Any suggestions on how to keep the rods etc. well lubed if you assemble an engine and then not run it for a while? I use this nice thick Lucas assembly lube which stays in place well, but after months, I'd think gravity would take its toll.

Is it ridiculous to think about inverting the engine for a short period with a little oil squirted in strategically through the sump opening with a turkey baster to get the rods lubed up under the piston skirts?

 

[650Skull]

if you were running rich then washing the bores could account for the scoring, and thrashing up to 9000 could cause the little end to get damaged.

You don't mention any thing about new con-rods, so they could have been near the end of their life especially if you ran past 7500 repeatedly in the previous 2 years before the 750kit. Who did the rephrase and did the con-rods get replaced.

 

[Tim of DO THE TON]

Again, just to clarify, these pistons are out of my old stock engine which rarely saw high RPM use. Mostly around town, casual rides on the highway from time to time. But I likely didn't break it in properly and it sat for at least a year between being built and running.

The engine I ran up to 9k was my carefully broken in 750 rephased motor with a Shell #1 cam grind, ported head and titanium valves/retainers.

The stock motor ran great the entire time, had 150+ PSI compression on both cylinders and was dead reliable. Only pulled it because I built the 2nd motor.

Didn't think about running rich / washing the bores of their protective oil. Will definitely keep an eye on that in my current motor and when I rebuild this one.

I think I'm just going to replace the pistons and rings and do a fresh bore. Just cleaning these up, honing the cylinders and replacing the rings will run me about $100. I can buy brand new coated +1mm coated pistons/rings for $150 tops and a new bore/hone is $100 for both holes. I think the extra $150 is likely well spent if for nothing else a little peace of mind.

Will be more gentle on the engine breaking it in this time around. Will also get the small ends of the rods checked before using this crank again. I do have another crank here if need be.

 

[angus67]

you do not mention new connecting rods, even though you agree they may be toast.

 

[daroberts3]

BelRay makes an assembly lube paste, designed to stay right where you brush it on. Just don't use TOO much. I have used it on Evo (HD) engines with good results. Proper break in, and heat cycling are sooooo important.

 

[Tim of DO THE TON]

I'll get the rods checked out. I do have a 2nd crank here so hopefully one of them will have good rods if mine are indeed problematic.

Correct me if I'm wrong, but replacing the rods requires pressing the crank apart and then back together, making sure it's all true and what not.

If I was going to spend money doing that, I'd go all-in and buy a rephased welded trued crank from Hugh and be done with it.

And if I was going to do that, I'd bin this engine and just take the good 750 rephased engine I have in my café and put it in this bike. I only insure 1 of my 5 bikes at a time so while the rigid is on the road, the café will be gathering dust.

Insurance on these old things up here in Canada runs $600 annually so I only do 1 of them. My BMW R75 just got its turn for the winter and will more than likely be ridden mostly next year while I finish this one up.

 

[angus67]

the crank assembly will need to be taken apart. some one here made hisown seperator with a threaded rod and bolts, nuts..get the welded counter weights, too