# Honda xr100r



## 1gr8bldr (Dec 21, 2012)

Rebuilding the top end. The timing chain jumped. I bought this thing from a teenager that has apparently tried his tools out on every nut. It was not running when I bought it. Every bolt on this thing is loose as if someone took it apart and just throwed it back together again. I bought it thinking that what he said was wrong would be an easy fix. He said something was wrong with the carb. I figured a good cleaning would fix the ethanol damage. But after getting it home, it soon became apparent that I should have checked it out before agreeing to the deal. I took his word on it and since he is the son of a friend, I'll just deal with it. Anyway, I've always heard that when the timing chain goes, that it will bend the valves. How do I know if the valves are bent? They are under much pressure from the springs. Do I need to remove them to find out? Or do they not move when bent? Thanks for the help. The last time I rebuilt an Polaris 350 motor I swore I would not do it again. I am not a mechanic but I got a pair of vise grips


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## Backlasher82 (Dec 21, 2012)

If you can get the cam timing set a compression test will tell you if the valves are bent. If you have the head off you can pour mineral spirits, contact cleaner, etc in the intake and exhaust. If the valves are bent it will leak past the valves.


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## 1gr8bldr (Dec 21, 2012)

Backlasher82 said:


> If you can get the cam timing set a compression test will tell you if the valves are bent. If you have the head off you can pour mineral spirits, contact cleaner, etc in the intake and exhaust. If the valves are bent it will leak past the valves.


I have it tore down. So if I turn it upside down, fill with a liquid and let set for a couple of hours, then look to see if I have lost my original level???? If it is all drained out or lower than when I started, they are bent????? If the level holds, then valves are good????


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## Backlasher82 (Dec 21, 2012)

1gr8bldr said:


> I have it tore down. So if I turn it upside down, fill with a liquid and let set for a couple of hours, then look to see if I have lost my original level???? If it is all drained out or lower than when I started, they are bent????? If the level holds, then valves are good????



If the valves are bent the fluid will leak past the valves just about as fast as you pour it in, you won't have to wait it'll be obvious right away. And yes, if it holds fluid you're good to go.


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## rayjay (Dec 23, 2012)

I don't know if Honda ever updated the cam bearings on the later XRs. The cam rides directly on the alum cyl head and this eventually wears out requiring a new head and rocker holder, cam, rockers, valves, seals, etc. If the head is worn badly there is a centrifugal oil filter made into the rh side of the crankshaft that should be opened up and cleaned out. This requires removing the main bearing on that side and destroying the oil filter cover to get it off. 

You also most likely need to replace the cam chain and both sprockets and both guides.  While the motor is apart I would replace the clutch plates, output shaft seal and inspect and repair the crankcase sealing surfaces that are just in front of the countershaft sprocket. When the chain jumps off it destroys this area letting water into the ignition cover. The ignition cover will also probably need replacing.

I used to refurb a lot of the XR80s, 100s and 200s and know their trouble points pretty well.  Did I mention the drive chain and sprockets are probably junk ? Same for the shock linkage under the swingarm. Probably have a lot of broken or missing spokes also.


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## Backlasher82 (Dec 23, 2012)

It's also possible that the cam chain was never adjusted and that's why it jumped timing.


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## 1gr8bldr (Dec 23, 2012)

rayjay said:


> I don't know if Honda ever updated the cam bearings on the later XRs. The cam rides directly on the alum cyl head and this eventually wears out requiring a new head and rocker holder, cam, rockers, valves, seals, etc. If the head is worn badly there is a centrifugal oil filter made into the rh side of the crankshaft that should be opened up and cleaned out. This requires removing the main bearing on that side and destroying the oil filter cover to get it off.
> 
> You also most likely need to replace the cam chain and both sprockets and both guides.  While the motor is apart I would replace the clutch plates, output shaft seal and inspect and repair the crankcase sealing surfaces that are just in front of the countershaft sprocket. When the chain jumps off it destroys this area letting water into the ignition cover. The ignition cover will also probably need replacing.
> 
> I used to refurb a lot of the XR80s, 100s and 200s and know their trouble points pretty well.  Did I mention the drive chain and sprockets are probably junk ? Same for the shock linkage under the swingarm. Probably have a lot of broken or missing spokes also.


Sounds like I should throw it in the dumpster and cut my losses


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## rayjay (Dec 23, 2012)

What did you pay for it ?  And you should inspect everything before making the decision. Maybe it already had a lot of new parts put on it. Unlikely, but possible


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## rayjay (Dec 23, 2012)

I just remembered something else. Does it even have the foam airfilter element in the airbox ?  With time the foam deteriorates and falls apart allowing dirt to go straight to the cylinder. This kills the valves and piston and rings and cylinder walls requiring a new bore job and oversize piston kit to match.


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## Backlasher82 (Dec 23, 2012)

1gr8bldr said:


> Sounds like I should throw it in the dumpster and cut my losses



Did you check the valves yet?


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## 1gr8bldr (Dec 23, 2012)

rayjay said:


> I just remembered something else. Does it even have the foam airfilter element in the airbox ?  With time the foam deteriorates and falls apart allowing dirt to go straight to the cylinder. This kills the valves and piston and rings and cylinder walls requiring a new bore job and oversize piston kit to match.


No foam filter, but the inside of the cylinder looks good to me


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## 1gr8bldr (Dec 23, 2012)

Backlasher82 said:


> Did you check the valves yet?


Yes, they are bent. Runs through as fast as you put it in


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## 1gr8bldr (Dec 23, 2012)

rayjay said:


> What did you pay for it ?  And you should inspect everything before making the decision. Maybe it already had a lot of new parts put on it. Unlikely, but possible


$300. No muffler, cut off over the foot peg, and no side plastic. I have now taken the half wore tire and switched it with our other xr100r, which had no tread left. The running xr100r would not run full throtle without cutting out unless you half choked it. So I switched carbs with the tore down xr100r. Now it runs good. If the parts were not so high, I would enjoy rebuilding it. Lucky for me that at least one is running good, for now. My son and his friend think they are a dirt biker gang


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## 1gr8bldr (Dec 23, 2012)

The running one, I bought from someone who claimed that it just had a top end rebuild from the Honda dealership. I suspect that it is so since it does not smoke at all. But it does have a chatter. What might this be?


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## 1gr8bldr (Dec 23, 2012)

I may cut my losses with the one and use it for parts. Or I have found an xr80r that has been robed of parts but the engine runs. Since they are the same frame, everything except motor, for $100, I could put this motor on my frame, and try to sell it to get back my money.


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## 1gr8bldr (Dec 23, 2012)

For now, since one is running, I should invest my time and money in rebuilding my smoking bad, Honda Fat Cat


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## Backlasher82 (Dec 23, 2012)

1gr8bldr said:


> The running one, I bought from someone who claimed that it just had a top end rebuild from the Honda dealership. I suspect that it is so since it does not smoke at all. But it does have a chatter. What might this be?



It could be a lot of things but I would adjust the valves and cam chain first. While you have the valve cover off see what kind of shape the cam and rocker arms are in. 

You can pinpoint the noise by using a screwdriver as a stethoscope. Put the handle to your ear and hold the tip to different places on the motor while it's running, you'll be able to hear what's going on inside pretty well.

A long handle screwdriver works best, you don't want to put your face on a hot engine or exhaust.


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## rayjay (Dec 25, 2012)

1gr8bldr said:


> I suspect that it is so since it does not smoke at all. But it does have a chatter. What might this be?



You need to get a manual. 

First pull off the seat and gas tank and wash the machine good so you don't get dirt down in the motor when you pull the valve cover off. 

Once the machine is dry pull off the valve cover and the ign cover and remove the sparkplug.

Using the flywheel turn the motor until both cam lobes are pointing upwards more or less. This will kinda keep the cam locked into position. Now rock the flywheel back and forth and see if there is a lot of slack in the cam chain. 

If so you need to adj the cam chain. Loosen the lock nut on the lower lh side of the cyl and then with a flat blade screwdriver loosen the set screw. The tensioner is spring loaded so it should move up automatically. Then tighten the set screw and the lock nut and see if you have removed the cam chain slack.

Sometimes the spring breaks and when you loosen the set screw the tensioner goes even looser. If this happens there are ways to adj the tension without having to take the topend apart and replace the spring. Let me know if this is the case.

NOW HERE THIS !!! It is better to have a tiny bit of slack in the cam chain. Just a tiny bit. Remember me talking about worn out cam journals ????  Having the chain too tight and constantly adjusting the tensioner accelerates this process [ I wish I had known this in the 70's when I had Honda singles  ]. 

If you look at your disassembled motor you can look at the tensioner and see how it works. You can see the shaft of the tensioner that the set screw bears against in the cyl casting. If the tensioner puts an excess of tension on the cam chain you can loosen the set screw and push down on the shaft of the tensioner from above with a small screwdriver. Replacing the head costs over $200 if you do it right so it doesn't hurt to spend a little effort in adjusting the cam chain to make the head last longer.

After you get the cam chain adjusted properly then rotate the flywheel so the cam lobe points directly away from the ex valve and then check and adjust the clearance as needed. Then do the same for the intake. Then reinstall the valve cover. You can reuse the gasket over until it starts to get hard. You don't need any sealer in these motors anywhere accept the ignition cover.

Anytime you have to replace the clutch plates you should install 2 heavy duty clutch springs straight across from one another. Using 4 is overkill for stock motors.


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## 1gr8bldr (Dec 25, 2012)

Thanks for the help


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