XR600 HRC urban legend...?

[hrc1]

I just wanna ask around and see if there is any truth to this, but i was talkin to some friends who said that the old 628 hrc kit bikes that ran baja had some issues with case failure and tranny failure. Somethin about the cases couldn't handle the added power and the baja gearset in the tranny stressed the cases and cracked them... He mentioned that the gearing up of the bike caused it to hook up almost too good and stressed it to the point of breaking. Has anyone had issues with increased compression or the big bore kits on there bikes? The only thing i found on the net was they referred to campbells xr600 as "the hand grenade". For being unreliable but it didn't go into datail...Just trying to shed a little light on this story. Thanks guys.

[phil_j]

Sorry I don't have any specifics, but I've always heard that stock, they finished no problem, but not fast enough. As soon as they were built up enough to keep up with the kx500s, they had reliability issues.

I think it has more to do with how it's run than how it's built, there are a lot of 628s out there, still reliably thumping along. But I don't know how many of them are running wide open for a thousand miles at a time.

This is, however, the first I've heard of the cases actually failing. You're not just refering to third gear failures, which this bike is known for after a LOT of miles?

[rmhrc630]

I just wanna ask around and see if there is any truth to this, but i was talkin to some friends who said that the old 628 hrc kit bikes that ran baja had some issues with case failure and tranny failure. Somethin about the cases couldn't handle the added power and the baja gearset in the tranny stressed the cases and cracked them... He mentioned that the gearing up of the bike caused it to hook up almost too good and stressed it to the point of breaking. Has anyone had issues with increased compression or the big bore kits on there bikes? The only thing i found on the net was they referred to campbells xr600 as "the hand grenade". For being unreliable but it didn't go into datail...Just trying to shed a little light on this story. Thanks guys.

all BS.

What you're mate ius talkig about is the 675cc monster Honda was forced to build when the big KX500s kept walloping Honda in the 500. HOnda simply could not match the 500 Kwakas and then built a hand grenade in the form of a 675cc beast.

The 628 HRC kit is well proven and futhermore compared to the 450s today positively under stressed.

[XR4DEZ]

Mine had the original Honda HRC 628 kit and the bike ran flawlessly for over 20K miles. I did not like that it needed race fuel and the high compression piston made it a pain in the rox with stalling. But in the open desert hit fifth and just keep building speed.The guy I sold it to is still riding the bike without a problem.

[bork]

Rob at barnums pro could tell you.

[hrc1]

Thanks guys. I just wanted to see if anyone else had herd of this. I'm not building one but a friend is with one of the ebay pistons and i just wanted him to feel better about putting that thing in his motor.

[Beyond The Pale]

Thanks guys. I just wanted to see if anyone else had herd of this. I'm not building one but a friend is with one of the ebay pistons and i just wanted him to feel better about putting that thing in his motor.

The biggest issue is that the HRC pistons are 11:1. This can be marginal with premium pump fuel. My understanding is that you can get heavy detonation in conditions that make the engine run hot like sand dunes or steep slow technical terrain on a hot day. I get light pinging on my 9:1 stock 600 in those conditions.

[amcgraw]

A former Honda mechanic was telling me about a somewhat similar problem when they tried to run the XR400 down there when it first came out. The final drive ratio had to be so high to get the speeds necessary, and it put unexpected loads on some of the engine parts. If I remember correctly, I think he said that they were breaking cranks because of it.

Not a 600, but I thought it might be a related issue.

[xrslagfan]

Older 600's had third gear problems. My 93 had over 30K miles on it when I sold it and no failures. The last 5-10K miles was with a Thumper big bore 660 kit and a 10.5:1 piston. I do however ride mostly above 5000 ft. which lowers the compression some. I liked the extra compression. Sea level may have been an issue.

My bike did have splines stripping on the countershaft from a lot of street use but it never failed!

[creeky]

I rode the crap out of my '98 HRC XR628 for three years with no mechanical problems at all. It needed at least a mix of 50-50 93 octane and race gas to prevent detonation under heavy pulling conditions.

[hrc1]

I was wondering about the compression being the factor since the cylinder wall isn't the roumoured thing thats failing. I have run high comp 12:1 pistons in air cooled motors before and have a buddy that builds race motors that has run as high as 13.5:1 in a 400ex with no issues other than they run hot.

Maybe a combination of the increased comp and the higher gearing stresses the motor beyond it's design, but i doubt the piston by itself if used with stock gearing would be an issue. Thanks for the feedback guys.