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Old 02-10-2014, 05:14 PM
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Default 1991 CR500 dual sport build

Let the fun begin...

Back in April 2013 I got a wild hair and decided I was going to embark on building a fully functional, street legal CR500. Since buying the bike I've slowly been collecting the parts I wanted for the build, and I'm finally at a spot where I'm ready to start the real work... going through everything, refreshing the motor and building it back up. I got started this weekend finally.

Here's what I had when I began:


And here's where it ended up 2.5 hours later. Sorry, no progress pics of the tear down.


The tear down was interesting, to say the least. The things I thought I'd have major problems with, like a stuck swing arm bolt, were no big deal at all. The things I never anticipated having any issues with, like a stuck bolt in the rear master cylinder, popped up now and again but I was able to get everything apart without much fuss. I'll need to do a little welding in a couple spots on the frame to repair some missing/damaged mounts. Once that's done the frame will go off for some powdercoat love.
In the meantime, I wanted to get a good look inside the motor so I can get the appropriate size piston ordered to get the cylinder work and crank balancing done. I'm pretty sure the motor on this bike had never been opened up before and was in surprisingly good shape on the inside.

Cylinder head


Cylinder. Cross hatch is still somewhat visible but mostly gone




Piston






The piston did have a couple little things I noticed. On the intake side there is a small line, it would just barely catch my fingernail. Looks to be a very small start to a crack


The exhaust side had some small, faint vertical scratches in it


I don't have a case splitter yet so I wasn't able to open up the cases, but the motor is all disassembled externally. It's so clean inside I feel almost guilty for tearing it all down, but I'll feel much better about proceeding with the build knowing everything is fresh inside. Now that I know what size piston I need, I can get my order in for the parts needed to refresh the motor (including my case splitter and crank puller ) and get the motor rebuild taken care of, then turn my attention to the chassis.

---------- Post added at 04:14 PM ---------- Previous post was at 02:32 PM ----------

Almost forgot... paging ossagp, dogger315, JMV, seanmx and the other 500 aficionados out there. Were the silencer mounting points in the subframe tapped from the factory, or were they just holes? The mount points on my subframe have no threads, and some non-OEM looking bolts were used that had nuts on the under side of the fender.

Last edited by cowboyona426; 02-11-2014 at 10:12 AM.
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Old 02-11-2014, 08:39 PM
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Quote:
Were the silencer mounting points in the subframe tapped from the factory, or were they just holes?
They are tapped into the subframe. I had to do a bolt and nut rig on one of the mounts on my 89 though cuz it was stripped out. No big deal. That was a clean starting point. I like that seat cover. Classic! You might decide you don't need to split the cases, unless you are set on the balancing. You can do crank seals from the outside. I just did them on my 89 last week. I was going to take pics and make a thread of it, but didn't feel like stopping and taking pics. Enjoy your project!
JMV

Edit: You might want to consider plating your cylinder, especially if you decide to balance. Then you won't be needing to do overbores. I did my 93 and just had my 89 done. Seems to work ok, but I only have 7 hours on the 93 and just put the cylinder on the 89 last night. Looks like you are at the first or .5mm over on the cylinder since the decompression slots are still there.
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Old 02-12-2014, 09:34 AM
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The cylinder is the original bore size. I'm not planning on plating it, with a fresh top end I'll get a good many years of use out of it before I ever have to worry about it again.
I'll probably repair the subframe to have threaded mounts, I have a couple ideas on how to accomplish that. I need to do it for the rear brake pedal bolt too because it was stripped out and poorly heli-coiled.
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Old 02-12-2014, 10:18 AM
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i have one cylinder that is original and never run. i am plating it before it runs. my reason is that it will be put together with a balanced crankshaft. you get quite a noticeable weight gain just going one size over.
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Old 02-12-2014, 11:58 AM
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What's a reasonable expectation for piston life on a 500? I can't see putting enough hours on this bike in my lifetime to ever need to go to the next size bigger bore. Change the piston out before it fragments and destroys the bore, hone and re-ring and you should get a good many years out of it, no?

This is starting to become exactly like owning a diesel truck. You can't change this without also changing this, this, and that. You can't fix this issue without buying this upgrade, which also requires you to buy this upgrade...
I may just buy a top end gasket kit, reassemble the motor and sell it all off in pieces.

Last edited by cowboyona426; 02-12-2014 at 12:12 PM.
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Old 02-12-2014, 12:31 PM
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This should be a good project. Remember when welding up any problems
areas, your frame is Chrome Moly. Make sure you use the correct shield
gas and rod.

As JMV said, those mounts used capture nuts. Easiest fix is to just clean
the back up with a flap wheel and weld in a new nut so you can use the
OE bolt again.

I'll have to disagree about splitting the cases. One of the key problems with
the CR500 is cracked cases in the vicinity of the kickstart stub shaft. It is
important to split the cases, strip them and NDI the Right side case for
cracks. These cracks aren't always visible to the eye until they really get
going. Catching one early is good because 1. you don't have to tear down
your newly rebuilt engine and 2. early detected cracks can be welded.
You can also check for any loose bearings, the main and countershaft
bearings are notorious for this. If you are fortunate enough to not have
a cracked case, I recommend installing a compression release. It's the
heavy duty kick starting that cracks the case.

dogger
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Old 02-13-2014, 12:04 PM
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about every right side case I have run across lately has tiny cracks visible around the the bearing on the pto (right side). some extend up and are visible around the oil passage in the transfer port. pretty easy to correct before it causes any shifts.
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Old 02-13-2014, 12:21 PM
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Everything is on hold right now until I can sort out which size piston to order so I can get everything needed, including the case splitter, headed my way.
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Old 02-13-2014, 08:01 PM
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Are these cracks you guys are referring to in the right case or the right case cover? Guess I never really looked at mine for that.
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Old 02-14-2014, 08:12 AM
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Quote:
Are these cracks you guys are referring to in the right case or the right case cover?
Right case. One of the first "signs" you may have a problem is either the
main or countershaft bearing on that side will spin in it's mount. This isn't
always caused by a crack case, sometimes it's just poor casting quality
(especially on new replacement cases), but if either of those bearings spin,
check the case very carefully.

I've had good success with a testing kit from Aircraft Supply that uses dye
penetrant and a blacklight to find hairline cracks even when the bearings
are tight. Once you locate any cracks, a TIG welder, carbide bit and sanding
discs can bring the case back to like new condition. Even after the repair, the
bearings may still spin. Here, you have a couple of choices. You can use a
TIG to pad the boss with a low, wide bead (just make sure the bead goes all
the way around), then grind and sand it until the desired interference fit is
acheived, or you can just use some Loctite 641 bearing retainer to lock it in
place.

dogger
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