600 Weak Tranny/660 Kit

I would like to post a little warning for those of you considering a big bore kit. I have an 86 XR600R that I have had since about 89. About 2 years ago I installed a 660 cylinder & piston kit and an "all around" cam. Have an FMF pipe and a Baja Designs street legal kit. I don't know if the trannies are the same on the later 600/650s but mine can't handle the power. I broke the trans. twice. 1st time broke a peg off of 3rd gear. It broke a piece off of the inside of the case, broke off the bottom of the new sleeve, and bent the piston. I rebuilt the whole thing again. 2nd time I kind of got lucky and it only broke a peg off of 2nd gear with no engine damage. I have not been riding this bike hard. The power is so fun but I can't afford the money or frustration of rebuilding this thing every year. I feel like I have to unload this thing now. Also if you install a bigger cam with a rebuilt, (most are rebuilt) you MUST use hardened rockers. Learned that the hard way. The manufacturer didn't mention it. Also my first rebuilt cam appeared to be porous and chewed up one of the stock rockers. The second cam (from a different manufacturer, also rebuilt) broke in great with hardened rockers. I am curious if any one else has had simmilar problems with the power up kit or tranny problems. Also If anybody want's a go at this bike let me know. I had the case fixed and the top end is all new. Sorry this is so long winded.

86/87 have tranny issues. The problem was corrected for the 88 model.

Having to use hardened rockers with a welded cam is pretty well documented as well.

i believe 3rd gear is still a weak point on modified 600's.

as long as you replace the cam and rockers together, they're usually pretty good. i've run a few cams like this(hardfaced) and had no problems.

My belief is that if you heavily modify anything, there will be side effects. Last year though I modded an '88 XR600 which had with no reliablity problems. The aim was to increase power without losing reliability which many people had that I know of after fitting 630/640/660 kits, big cams and the like.

The mods were as follows-

*inlet port in head tidied up but not altered (polished)

*head shaved 0.5mm (or 20 thou) to achieve a higher compression ratio without resorting to using a clumsy and heavy aftermarket piston. Therefore, extra stress to the big-end bearing etc is kept at a minimum as the stock Honda piston was used.

*Stock exhaust replaced with Staintune stainless steel full system, which is claimed to increase power 10% throughout the rev range.

*Main jet was increased from a 165 (stock) to a 168. Airscrew richened from 2.5 turns out to 2.75 turns out. Other than these two minor carb alterations, the carb was stock, although the stock choke butterfly was replaced by an aftermarket one with no flap.

*The stock clutch was used save for replacing the standard clutch springs with White Bros items.

The power difference I experienced with this bike was very encouraging as the bike (with these mods) would now run dead level with a particularly good WR400 I had at the time, as well as numerous WR426's- much to the surprise of my riding mates! The bike had gained around 8 rear wheel horsepower as well as more torque. I continued to cover many kilometres on this bike completing around 3500 kms of dirt riding before finally selling it with the engine still running as sweet as a nut!

If I could have all the money back I spent on mods and the breakdowns, I would put it into a WR or a new 650. I just got too attached to the thing after 13 years and its low-end grunt. I have driven some WRs and they seem to have close to the same power, but rev so much higher and freely which is pretty addictive, as well as the weight and suspension improvements. I've got the XR geared up for the road and open trail, but it will still pull up a pure power wheelie in 3rd gear. She will do about 100mph according to the factory digital speedo when it's not windy. I am pretty sure I broke the tranny this last time snortin up a steep hill in 2nd gear at low rpm. It started having shifting problems about 10 minutes later down the trail when I got back into the low gears again. I finally purchased a cam chain tensioner holder tool; man is that spring a pain to get back in place without it. Does anybody have an opinion as to whether the higher gearing added to the tranny stress?

i know 2-3 people that have broke 2nd and 3rd gears one of the dogs broke off he put it back together less one and it was fine 1 1/2 years almost before it broke another one off then he bought new one to reolace it i just broke the gearshift spindle in mine hope nothing else will know tommorrow we are riding 93 and up 600s

You guys have been pretty unlucky with your tranny's! I've owned 4 different XR600's and mates have owned a further 2 and none have had any sort of transmission failure! That said though, all had stock engines save for the one I modded as described in my last post. :cry:

Well, torque is what breaks transmissions and since XR600s & 650Ls make alot of it, it is harder on the trans. Bigbores make it worse, but I think usage contributes alot as well.

It would be cool if the aftermarket had gearsets with more dogs or fatter ones. I wonder if cryo treating helps at all?

I have an 86 XR600 that I bought new and it is basically stock with the addition of a pipe and jetting.

I have been through 2 second gears and 1 third gear.

They are simply WEAK :cry:

It is difficult for me as well to give this Bike up, too much history and memories.


Mmm, the 600's that I and my friends owned were 88, 92, 94-95 models, I have a feeling honda changed a few things for the 88 RJ model for better reliability, so I think they're better than the earlier versions RF,RG,RH. I think the maintenance history of the bike would have a bigger bearing on tranny life though. Don't dispair though, there are many bikes with weaker gearboxes eg my WR400- 10 rides old when I bought it, 2 rides in it starts jumping out of top gear! To say I was a little peeved would be an understatement!

I believe they fixed the tranny problem by 87, seen it listed on one of those pages listing changes every year, and my 87 hasn't had any tranny issues. David

If you were to buy 2nd and 3d from the 88 maybe that would solve it? Maybe the gears you have bought are the later version. Or is it the design that was changed for 87?? anybody know?

the ones i have seen seemed to have broke while givin it gas landing off a jump

snapped one of the dogs right off

I've been thinking about it and the fact that only one dog breaks off at a time leads me to believe that the gears arent machined as precisely as they could be. Otherwise either none would break since all the load is spread over three times the area or all of them would break off. Just a theory.

i thought the main problem was with the actual gear teeth slowly wearing through the outer hard facing then failing altogether. I have only heard of the geardog problem being very occaisional. I also have a clymer workshop manual which states that the 88 on models have a bushing in the countershaft 3rd gear and mainshaft 4th gear, so maybe this was to combat these problems.

That would lead you to believe that the gears are not lining up correctly right!The first gear that broke had one side chewed up as though it wasn't fully in gear and that would explain the single dog breaking too. maybe the problem is that the barrel is not shifting fully into gear or not holding in gear.

I seem to remember in the HRC power up kit it came with a different gear for the primary drive. I think they wanted you to change the small gear on the crank and the clutch basket which had a different gear. Doing this changed the ratios an made the tranny spin slower which in effect makes it stronger giving it more leverage against the counter shaft. Again my memory is not what it used to be. :cry:

Mmm i read something along these lines in a special article in one of our oz mags. The feature was on an XR600 safari bike decked out for desert racing. This bike featured the hrc clutch basket and primary drive gear which made the gearbox spin faster (higher ratio - the same as gearing bike down) so as to decrease the wear to the transmission gear teeth. As far as i can see, the XR6 only gave problems under extreme conditions- long hard desert racing, highly modified engines, or long term plain misuse. My XR6's have been super tough.

The first time I broke 3rd gear. One dog broke off and took half of a tooth with it. The gear it mated with was like new. At first I thought the gear tooth failed and took the dog with it. But the second time I broke 2nd gear and it just broke a dog off. But it's mating gear had wear marks where the dog slides into. This could be a problem with it not engaging fully, but I think it was from me trying to get the thing out of first gear with the broken off dog wedged between. I think the dogs are just weak. When I replaced 3rd gear I replaced it's mating gear just to make sure that all three dogs would take the load equally. When I replaced the second gear it only came in a kit with the gear, mating gear, and a new fork right from Honda. This leads me to believe that they might be aware of a problem. I compared old and new forks, no problem with the old one. It shifts fine but now I am scared to ride the thing. I drove this bike stock from 1989 to 2002. Always shifted good and never popped out of gear. Never had a problem till the power up kit. I think it is a pure power issue. :)

In regards to "XR6's Rule"s previous post about the different clutch basket and crank gear, having the gear box spinning faster does make more sense to me than slowing it down. Maybe the fact that I have it geared up quite a bit is part of the issue. By being geared up the tranny has that hard "long" pull before you get to the next gear. You are forcing the bike to get up to a faster speed with the same gear. Your bike feels more powerful when it is geared down, but that doesn't necessarily mean it is harder on the tranny, does it? With lower gearing you get into the next gear quicker. You aren't forcing one gear to do all the work. 1st gear is so low that you are hardly ever in it if only for a short while. In 1st gear on the pavement, I can't open up the throttle all the way, it will simply go over backwards. 2nd and 3rd gear have a much wider spread and take the torque longer. By the time you get into 4th and 5th the counter shaft is spinning way faster and the bike has less torque to the wheel. The more I think about it, it makes sense to me that 2nd and 3rd would go first. Any mechanical engineers out there? The bike wasn't designed for that much power and use on the pavement. In the dirt it isn't as big of a problem because the tire spins. I'm guessing that I might have broken 3rd doing 3rd gear wheelies on the pavement. I think I might have broken 2nd gear lugging it up a steep hill too slow at low rpms so the wheel wasn't spinning. The problem didn't show up right away either time, so it is hard to tell. It's too bad that someone doesn't make machined gears out of harder steel than the factory cast ones.

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