Mystery camshafts. Not 3H5 Or 2H7

[Orange4]

I read through the engine ID thread but my shafts are marked 3B for the intake and 9X for the exhaust. Any insights? Bike is a Canadian 79 standard. Engine matching VIN.

[crazy steve]

Probably service replacements or possibly aftermarket. There's specs and the procedure for checking the cams in the factory manual.

[Orange4]

Checked carefully with a vernier caliper, I measured .334 in. lift on the intake and .316 in. lift on the exhaust.

That's lower than stock 78 no? Read somewhere 80+ lift is .345 Is the 79 lower lift that the 78? Then it all makes sense.

You would think a regrind would be higher unless the original owner was after low end torque.

[crazy steve]

You should have .347 lift on the intake, .020 less on the exhaust if they're 78-79 cams, the 80-82 cams are .347 lift on both but have less duration.

Probably later service replacements, as it's not uncommon for manufacturers to 'detune' replacement parts...

[Orange4]

So now they are steampunk candle sticks...

Unless someone wants to de-tune their XS...

...crickets chirping.

[fredintoon]

So now they are steampunk candle sticks...
Unless someone wants to de-tune their XS...
...crickets chirping.

Hi Marcus,
lift height ain't a camshaft's only criterion, just perhaps them candlesticks will work real good, eh?
Didja ever run the bike with those cams in?

[skids]

So Steve, would you use those cams and if so, would you keep the shim clearances tighter on that side? Like just one shim size?

[crazy steve]

So Steve, would you use those cams and if so, would you keep the shim clearances tighter on that side? Like just one shim size?

I'd look for a set of 2H7 cams...

[Orange4]

Thanks Steve,

Previous owner of my 79 (built in 8/78) bent all the valves so I found a later head/jugs with the bigger valves that was is in such good shape I got them even though they are not 78-79.

I know I will have to check clearances but I'm planning to get the head shaved to keep the compression. Is there enough meat on the stock pistons to increase the valve pockets if I need the room?

Another route I was thinking was to weld the domes higher on the stock pistons. Is this a possibility or too much danger of warping/cracking? I am a fabricator and I have a TIG welder so I can pull it off but don't have the experience with automotive applications

Thanks.

[mrbisbob]

Welding piston domes

As a professional motorcycle performance machinist I would say that welding the domes of those cast pistons or any pistons would ruin them. The biggest risk would be changing the dimensions of the ring grooves which are very tight. The next problem would be accurately profiling the "new" piston domes to be consistent from chamber to chamber. Next would be removing the heat treat on the aluminum making it softer. A better way to get a little more compression would be to tighten the squish clearance by leaving out the base gasket and using yamabond in its place. Its an easy .5 mm with no machining of critical parts and when combined with milling of the head can increase your compression a significant amount. You would have to check your valve to piston clearance as you intend to run the cams for a minimum of 1mm IN and 1.5mm EX. If you can't get those clearances then you would have to machine the valve reliefs to get more room which will of course reduce the size of the dome a small amount and the compression ratio with it. If you use smaller lobe centers when you degree your cams you can generally increase bottom end torque. Hope this answers your questions.

[crazy steve]

Your best bet is just swap the whole top end; head, cylinders, and pistons. You can mill the head, but that will change your cam timing and open yet another can of worms.

These are great motors, but spending money on custom machine work for these has been proven to not be productive...

[Orange4]

All I really need then to do this the easiest way is the newer pistons. I guess I'll need to start asking around.

Thanks.