finally took apart 89 xr600 engine


10 replies to this topic
  • DSTerry

Posted January 26, 2006 - 01:33 AM

#1

I finally found some time to strip down my engine and figure out why it was burning about 1 quart of oil every 20 miles. Actually, getting pulled over by a motorcyle cop today asking why my bike was smoking so much had a little to do with it. No ticket though!

To my surprise, it wasn't what I thought it would be, piston, rings, seals. I'm still not 100% sure why it was burning the oil so badly, but here is what I found.

The camshaft lobes and rocker arms were comlpetely worn out. The arc on both the exhaust rocker arms were actually worn into a valley, and the cam lobes were pretty flat. But on the good side, the valves, valve guides, piston, and cylinder all looked brand new, and measured well within the service limits.

Here is what I measured:

Cam lobe
Ex-Rt = 1.207
Ex-Lt = 1.178 (ouch)
In-Rt = 1.220
In-Lt = 1.215

Ex service limit = 1.220
In service limit = 1.222

This must be why it was burning oil because everything else looked good. But not quite sure why exhuast valves not opening very far would do this.

The rest of the parts:

Piston = 3.817 (limit = 3.813)
cylinder = 3.824 (limit = 3.824) This is a nikasil cylinder

Ex-Rt
valve stem = .2595 (service limit = .258)
guide = .261 (service limit = .261)
outter spring = 1.46 (service limit = 1.38)
inner spring = 1.30 (service limit = 1.34) ????????????
Ex-Lt
valve stem = .2595
guide - .261
outter spring = 1.458
inner spring = 1.30
In-Rt
valve stem = .260 (service limit = .257)
guide = .261
outter spring = 1.46
inner spring = 1.30
In-Lt
valve stem = .260
guide = .261
outter spring = 1.46
inner spring = 1.30

Thats pretty much everything I measured tonight. So one big question is do I need new inner springs? It seems odd that all 4 inner springs are out of the service limit exactly the same. Could the Honda manual have a misprint on the limit for the inner springs?

I plan on replacing the cam, cam bearings, rocker arms, valve seals, piston, pin, clips and rings. I'll clean up all the ports and chamber, and lap the valve seats. Though I might take it in and get a valve job since the exhaust seats are pretty pitted.

This is my first XR motor I have pulled apart, so if anyone experienced in rebuilding these motors has any comments on the items I measured, or items I plan on replacing, please let me know.

And the final question, since I need a new cam and possibly springs, should I stick with the stock ones, or get an aftermarket higher performance one? I could always use more power! Anything else anyone can suggest to do during my rebuild. I don't want to get to involved but if I need to replace the parts anyway.

Thanks for all the help. I am looking forward to finally riding a non oil burning, badly smoking XR.

  • snaggleXR650

Posted January 26, 2006 - 05:16 AM

#2

The springs will loose 'spring' over time. Heavier duty springs would be good, but it sounds like you got your $'s worth out of the OEM springs. I'm not a motorhead, so I can't comment much. It sounds like you have a pretty good handle on things. I would get down and check the crank bearings (big/small end). Surely they have some play by now. You could save a bundle if you could do it all yourself, otherwise try to find a good builder. Good luck.

  • rsstom

Posted January 26, 2006 - 07:01 AM

#3

There's a bearing surface in the center of the top cover and head. It supports the cam there. What does that look like? This area will score pretty badly in a low oil situation.
Have the cylinder meassured to see if you'll need to bore it.

  • bigboredbiker

Posted January 26, 2006 - 07:21 AM

#4

Firstly, if you have a nikasil cylinder, don't rebore it unless you are prepared to replate it! It will be cheaper to find a used motor and rebuild that. Ask the guys on here if anyone has a top end from any xr600 '91 on. Honda dropped the plated bore about that time if I remember ok. Check as well that the cylinder/piston hasn't gone oval by measuring their diameters at least 10mm down the bore and piston. XR motors seem to have a habit of wearing out-of-round like mine did. I rebored 0.5mm, new piston, new rings(make sure they're top quality like Honda OE), gaskets etc for under £200 ($170). Good luck!

  • DSTerry

Posted January 26, 2006 - 11:35 AM

#5

Piston and cylinder look great. I already measured everything and they are within specs. I mentioned it was nikasil because thats what the bikes originally came with. But being that it looks so new, maybe it was already re-sleeved.

I don't know the history of this motor since I just bought the bike with the oil burning problem, but the cylinder looks brand new inside. There isn't a single score mark, and some of the cross hatching still shows. The piston looks the same. I'll measure the ring gap tonight, and if that is still well within spec, I'll probalby just use the same piston and rings. The lower end seems perfect. There is no up/down play in the rod. The guides and valves also measured well within the service limits. No play at all in the valves. There was only .001" difference between the valves and guides.

It almost seems as if this motor was recently gone through. Unless XR motors always look good and don't wear out very often. Or it just wasn't ridden hardly at all, at sat in someones garage 11 months out of the year.

So the only problem I am dealing with is the worn out camshaft and rocker arms. The center of the head were the cam sits does look a little scored. When I pulled the head cover off, there was tons of oil up their. But could I have a problem with not enough oil getting to the top end?

On the other hand, the valve train may have never been adjusted. If the valve adjustments were way off and the bike was still ridden (even a little), could this have caused the cam and rockers to were prematurely?

I'll buy the parts I need and rebuild it, but I don't want to put it back together and have it wear out quickly for some other reason I over looked.

Thanks.

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  • bigboredbiker

Posted January 27, 2006 - 02:55 AM

#6

It will be well worth throwing a new set of honda oe rings at it tho....while it's in bits. I had the smoke problem when I rebuilt mine, turned out to be crap(new) rings. Suddenly stopped smoking when they got replaced with genuine oe jobbies :thumbsup:

  • DSTerry

Posted January 28, 2006 - 01:23 AM

#7

Yes, I always stick with the OEM parts. I rode and raced 2 strokes for 10 years, and when it came to pistons and rings, I only used OEM and never had a problem.

I finally figured out the main reason why the bike was smoking so badly. The oil ring on the piston lost all its spring. It wasn't stuck in the piston, but it did not stick out at all.

Looks like the bike might have ran out of oil at some point in its life and overheated pretty badly. Thats probably when most of the damage was done on the camshaft and rocker arms. One of the cam bearings looked burned too.

So after re-checking everything, looks like the cylinder is about .002" out of round, has about a .0015" taper, and the mating surface is very flat. Since these are still within the service limits, and their is no aparant wear marks anywhere, I'll run the cylinder as is.

Do you typically hone a plated cylinder?

I'll also be using the same piston and pin. These were also well within the service limits. The rings will be replaced. I measured the end gap, and they were very worn. (.068" and the limit was .026"). The valves and guides all looked great. I will re-grind the valves and seats just to make them perfect. And some new seals will be used.

And finally a new stock OEM camshaft, bearings, and 4 new rockers should complete the rebuild.

I still need to check the oil pump and passages to make sure the top end is getting enough oil.

Hope to have the thing back together and running in about a week.

  • bigboredbiker

Posted January 28, 2006 - 04:36 AM

#8

Personally I wouldn't touch the cylinder with anything but an oily sponge. The wear, as you said, is minimal and within limits..just. Looks like it has had the same monkey riding it as mine....do people not know where the oil filler is?? lol. Throw those new rings at it bud...and ride the pig 'til it squeals :thumbsup:

Tell us all if it works! Good luck...

  • XRsteve

Posted January 28, 2006 - 07:12 AM

#9

The damage to the head/cam could easily have been caused by having run the engine with the oil filter in backwards. This cuts off oil to the top end. I bought a bike (99 650L) that this had been done to and had to replace the head, cam, rockers, piston, etc. Luckily, I got the bike from a dealer that ended up buying the parts. I still have the old parts. I could post a pic of the head and rockers so you can compare it to yours. It sounds like somebody had the filter in backwards and then fixed it pretty quick.

  • DSTerry

Posted January 28, 2006 - 09:54 AM

#10

Good to know about the filter. That could always be a possibility. The guy I bought the bike from seemed to have no mechanical experience what so ever. He told me I had to pull off the gas tank to change the spark plug!

I took the camshaft and rockers to my local dealer, and to a local machine shop run by an old guy that everyone knows and trusts, just to show off how worn they were. I also took the head so the machine shop could see if their was anything they could do about the center bearing surface. It was scored. He said their wasn't anything he could do, but that I should just run it.

But all is good since I had already figured I was going to be spending money on the motor when I bought the bike, and the amount is actually less than I guessed. I figured worst case just to be safe. I didn't want to end up putting more money into it than it's worth, but I still haven't reached that point yet! And I wanted a project that I could rebuild from the frame up, which is what I got.

  • pcmartin

Posted January 28, 2006 - 11:40 AM

#11

Let me make a few suggestions. First have your cylinder ball honed before you put in new rings so they have a good surface to seat against. Second be sure to install new valve guide seals. Your head damage is caused by lack of lube or over heating. Both will cause your valve guide seals to harden and need to be replaced. And third, the journals where your cam ride can be welded an then milled as a method of repair. there are several places who this type of repair.





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