Jump to content
Sign in to follow this  

RM85 Bottom End?

Recommended Posts

So my son's RM85 needed a top end and we ran it till it quit. :moon:

Shop got it apart and it started to seize. There was some damage to the piston and cylinder. Not horrific, but I'm not sure how bad, is bad?

They want to do the bottom end as well...

So, what kind of horrible things will happen if I do JUST the top end?

Cylinder was sleeved. Does that require re-sleeving or can it be bored?

I can get an OEM cylinder for $220 or re-sleeved for $235. Is a sleeve better than an OEM cylinder?

Any thoughts?

Thanks,

John

Share this post


Link to post
Share on other sites

An OEM cylinder will be superior to a sleeved cylinder. As long as the bottom end has no play in the rod or crank bearings it will be fine, unless metal shavings got in.

Share this post


Link to post
Share on other sites

IF the bottom end goes, you're looking at a crank, cylinder and piston.

The mains are cheap, and a rebuilt crank is not all too expensive either.

Your sleeved cylinder can be bored, I'm at .060 over on a stock steel sleeve from the 80s. Some guys on this forum are hellbent that sleeves are "crap", but they're just old tech. I've seen coatings flake, how can you get spun steel to flake?:moon:

It's easier to do the bottom end while they've got it, rather than have your mains seize 40 miles from nowhere.

Share this post


Link to post
Share on other sites

Get the cylinder replated by a reputable company like Powerseal USA or LA sleeve. They will bring it back to brand new condition and OEM specs for around $150. I would do the bottom end while I was in there as well. I would even replace the crank with a Wiseco Hotrod crank kit.

I'm not a big fan of resleeving cylinders, but do believe it has its place. I have also seen them drop out, twist and shift before as well.

Share this post


Link to post
Share on other sites

OK...

Just picked up the bike from the shop with plans to tackle it myself.

No damage to the cylinder. The perceived damage from the shop that generated the desire to rebuild the whole friggin' bike is port work. There is no slop in the rod, so no obvious damage to the bottom end.

Just mic'd the cylinder and there is no measurable difference between the top and bottom.

I'm going to order a top end kit on eBay for $84 and give it a shot.

I can't justify much $ when it's a kid's play bike.

Share this post


Link to post
Share on other sites
OK...

Just picked up the bike from the shop with plans to tackle it myself.

No damage to the cylinder. The perceived damage from the shop that generated the desire to rebuild the whole friggin' bike is port work. There is no slop in the rod, so no obvious damage to the bottom end.

Just mic'd the cylinder and there is no measurable difference between the top and bottom.

I'm going to order a top end kit on eBay for $84 and give it a shot.

I can't justify much $ when it's a kid's play bike.

It may be a kids play bike but those bikes run at a very high rpm, but it sounds like you have it in check.:moon:

Share this post


Link to post
Share on other sites

Personally, with running these bikes (65 and 85) I would just do the top and bottom.

I throw an hour metre on my kids bikes to let me know when maintenance is required as keeping track in my head is getting tougher and tougher (40 next month!!!!). If you know the bike might get 10 -15 hours is all then fine, don't re-build but if it they ride like my kids do (80-100 hrs/yr of play ride) then do it all.

My perspective is a little different though as the older son has to pass down the bike to the younger one so upkeep and maintenance are important.

Good luck.

Share this post


Link to post
Share on other sites

rebuilding the bottom end isnt all that hard at all. you can get all the tools you need at rockymountainatvmc.com, they have extremely helpful intructional vids on how to do it as well. and crank bearing and seal kits are around $40. and what do you mean you ran it till it "quit"?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...