1985 250R Piston Damage

[oscarmayer]

It is fixable. And take your time and do it right. Replace the reeds too.
That plug. Good lord!!! It is nasty!! Like 80 yr old hooker nasty!! Seriously!!


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[poolieZerUK]

I have a Tri z motor bought as a non runner, had the same thing.
Had been freshly bored and virtually no chamfer on the ports, bits piston ring had got into the big end and fecked it showing heat scorching.
Looks to me like whoever had that apart wasn't too competent so it may also have had an air leak as well as all the other suggestions here.
Check the carb boot/manifold condition too.
Good luck with it.

[RIDE-RED 250r]

It doesn't take much run time with bits of compression ring floating around in there to do serious damage.

I would strongly recommend a full tear-down and rebuild. With an entire ring AWOL, it is unlikely that none of it went downstairs. And if some did, some level of damage to the crank bearings or lower rod bearing is likely to have occurred.

Besides, you are going to fix the top-end right, why not do the whole job and be sure you have a good engine top to bottom. You are looking at about $250 for a rebuilt stock stroke crank, $50 for new crank bearings, and $50 for a complete gasket set, ballpark. Just as things like compression rings can do damage to the bottom end if they fail, bottom end failures can do damage to the top end. Little bits blow around like that in a 2-stroke when they let go. I have seen lower rod bearing failures do damage to pistons, domes, and cylinders more than once.

[Helidaddy]

Replace the reeds too

Just curious because I'm new to two strokes… What do you think I need to change the reeds for? Old age? Or possibly leaking? When I bought it, he had a couple of Boyesen stickers on the bike. I should take a picture of the reeds.

[QUOTE=poolieZerUK;1365325.
Looks to me like whoever had that apart wasn't too competent so it may also have had an air leak as well as all the other suggestions here.
Check the carb boot/manifold condition too.[/QUOTE]

That's what started this whole thing… I made a leak down tester after learning about it. I tested the engine and it only lost 3 psi in 12 hours… Started with 7psi, ended with 4 psi. THEN I noticed the piston.

I would strongly recommend a full tear-down and rebuild. With an entire ring AWOL, it is unlikely that none of it went downstairs. And if some did, some level of damage to the crank bearings or lower rod bearing is likely to have occurred.

Yeah. I'm doing the rebuild with the feedback you guys have given, which is EXTREMELY appreciated!! As a side note, the rod big end side clearance is .023" and I can't feel ANY radial play in it.


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[oscarmayer]

Since you were running lean some how, there is a possibility the reeds got damaged or were causing the air leak. reeds are cheap. $35 for a nice set of racing CF reeds and cheaper for stock oem replacements. It is a good idea to replace the reeds often. In racing we replace them every 6-8 rides MAX. I know guys that replace them ever 4 rides period. They feel the savings is not worth the end results on a $2500 race motor and I tend to agree. If your going to rebuild it. put a nice set of reeds in the thing and then replace the reeds every so often for insurance. it's like getting a new valve job every so often. It helps it run smooth and purr longer.

[RIDE-RED 250r]

Reed petals need to lay flat on the block to seal properly. When they start to wear and not lay flat on the block, you can experience hard starting, and in extreme cases blowback through the carb. They literally are a 1-way valve. They are supposed to open when there is negative pressure in the crankcase as the piston moves upward to take in the next intake charge, and then close up as the piston moves downward. They move at a very high rate of speed, opening and closing every time the piston moves up and down. I'm sure you can see that damaged/worn reed petals can be troublesome.

Also, reed petals chip and break over time. The reed fragments that break off get pulled into the engine. Sometimes they blow right through and into the exhaust, other times they take the grand tour of the engine and can do some damage. The old steel reed petals were more likely to cause some damage. The carbon fiber reeds are less likely to do any damage, but it has been my experience that they do not last as long before they start to chip on the edges. It is said that reed stops can increase the life of carbon fiber reeds. It makes sense to me.

[*ATC*]

Simular problem this Feb, air box lid left off. you see where I'm going, yes lite sez, but took this long to scrape money up for .25 piston and cr head gasket.
Fired up to night souds great,

[Helidaddy]

Well, I'm glad I took your advice. Even though the case was leak tight, look what I found...


So who around here is the best to weld up the case? After searching, I've found a few people happy with BDT. I have some work to do around the sprocket area that needs some material added also, but the case saver bolts up and no cracks there, just some aluminum ground down pretty good from the chain the PO threw.

That being said, What are the opinions on places to get bearings and gaskets. Some people say to get Honda gaskets but can't figure out why they say that. I've heard of an upgrade to the 8 ball bearing from some other bike, I think a CR500, and I'm wondering if it's necessary for a stock motor. Looks like the cost is going to get out-of-hand soon for a stock rebuild but love these machines so it's all good.

[yaegerb]

BDT to weld up your cases....bar none...they have an excellent welder named Rob Selvy
Search eBAy for discounts on bearing and seal packages. OEM is piecemeal and expensive but the best way to go in quality...your choice.

[atc300r]

Thats almost identicle to the damage to my 85 250r case, I sent mine to BDT and they did a great job on it.

[Helidaddy]

Yep. I saw your thread earlier and I thought that it's weird that you had the exact same damage in the same spot. I'm sending my case to BDT for sure. How long did it take to get it done?

[atc300r]

My cases were gone about 3 weeks but I live in NY and had to ship them. If you call them first they will tell you roughly how long it will be. When they got ready to do my cases they called me then when they were done they called me to tell me the price. I have another set Im going to send as soon as I get them ready.

[RubberSalt]

The rings went out a long time ago. You can see the damage UNDER the carbon on the piston. This engine didn't over heat to to bad. Severly over heated pistons will show a 4 or 6 point seisure. This doesn't have any just crown damage. The exhaust side of the piston was NOT prepped for the engine. The 250r should have a 2 holes drilled in the piston for lubrication.

Odds are that incorrect rings were used, to small of a gap. The rings cought a port, snapped off, got stuck under the crank, broke the case, rings went up top and chunked the piston up before leaving the engine. After the hole was formed, it leaned out and got warm.

[86T3]

I've read this thread twice now and can't get over the amount of knowledge you guys have. I look at the picture and think,"Man, that piston I'd dirty" and am happy with my analysis. I guess this is why I have people build my motors. That's it, carry on

[Helidaddy]

So, I have another issue to deal with. When I took the stator cover off, I found the counter balancer bearing holder long bolt had broke off at the threads and was rattling around in there for a while because I could see that the end of the bolt was shiny and smooth. For a while I couldn't figure out what happened because when I looked inside the right-side case where that long bolt goes, you literally can't tell there's a snapped-off bolt in there because it is all smooth like its just a hole that bottoms out without threads. After looking closely I barely made out where the broken part of the bolt is. So how do I get that out? I've snapped my fair share of drill bits while trying to remove broken bolts before and it's something I don't want to ever do again lol. I've searched and read that this is common but nobody logs their adventure of getting it fixed. Does anyone know why this particular bolt snaps off in these engines? All my bearings were in good shape but I'm replacing everything anyway, so I can't figure out why the bolt snapped.

Any help/feedback is appreciated

P.S. YES, I am mechanically inclined