xr-crf maintenance

I had an opportunity to get my dads 85 xr600 running, and it was fun seeing just how different the crf and xr motors are. the caps for checking the valve clearance and the set screws for adjusting them are awesome, would be sweet if the crf had that capability.

do you thin that if somebody developed a valve cover with removable caps, and rocker arms with adjustable screws for the x that it would work out? you would probably need different valve springs to accommodate the the extra mass of having a setscrew and jam nut. would be nice to do away with the shims, and having to take the whole shebang apart to change them. i know, LAZY. i love working on bikes so it really doesnt bother me, it just got me thinking. what do you guys think?

I think it would make the motor to tall.

I had KTMs for 10 years and I much prefer the shim & bucket over the rocker arms with adjustable screws. It was always a PITA to coordinate the feeler gauge, screwdriver and 10mm open end wrench. I've never worked on a XR head so maybe it's easier and roomier, but the KTM RFS valves were a PITA to adjust in my humble opinion.

The shim & bucket is so incredibly easy to check and, most of the time, if you're keeping the air filter clean and regularly changing oil, you don't need to mess with shimming except maybe every 150-200 hours or so.

One little shortcut for the exhaust shims on the 450x - you don't need to remove the cam holder to change the shims. You can just remove the cir clip that holds the rocker arm shaft in place and lift out the rocker arm to replace the shims. Granted, most of the time the intakes valves are the ones that require shimming, but just a little shortcut I learned.

There are plenty of theories on which design is better. I'm not an engineer so I can't really comment :cheers:

Shim buckets are a better design for high rev motors IMHO. I've checked and adjusted many valve tappets in my day and if I never have to do it again I"ll be happy...including on XRs. CRF motors are more efficient and easier to work on then the XR's. That's not to say they need less work but the top ends on the CRF are about as simple as a 4-stroke can be.

As an aircooled Volkswagen guy, I love the adjustable rockers on my old engines. They're easy to adjust. They're also a low RPM, very different engine.

Having said that, I'm not a fan of modifying stock internals unless well proven. Not sure if I'd throw down the cash for something like this or not...

Was that helpful?

Kyle

all very true, and i definitely dont want to move back in time evolution wise. just got me thinking. thanks for the replies.

Shim buckets are a better design for high rev motors IMHO. I've checked and adjusted many valve tappets in my day and if I never have to do it again I"ll be happy...including on XRs. CRF motors are more efficient and easier to work on then the XR's. That's not to say they need less work but the top ends on the CRF are about as simple as a 4-stroke can be.

Shims are a higher-tech formula one design for engines that rev to the moon. They can't break and scatter valve train parts into the engine nearly as easily.

I had KTMs for 10 years and I much prefer the shim & bucket over the rocker arms with adjustable screws. It was always a PITA to coordinate the feeler gauge, screwdriver and 10mm open end wrench. I've never worked on a XR head so maybe it's easier and roomier, but the KTM RFS valves were a PITA to adjust in my humble opinion.

X100 It was a PITA to try and adjust the valves on my old Husky which had the adjustable screws. Infact I ended up taking it to a shop to have my valves adjusted because I didn't want to deal with it. On my CRF, I can have my valves adjusted in 30-45 mins and I'm sure they are done right. :ride: If the CRF ever went to the adjustable screw design, I'd sell my bike and get something else. :cheers:

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