Is changing valve springs and guides necessary?

ShadyOne

Member
Pretty self explanatory in the title but a little more info.
I have the heads and cylinders off my 81 XV750, it's got 55,000km on the clock and prior to removing the head it had 145psi and 135psi in each cylinder so plenty of compression.
I will be replacing the cylinder gasket, head gasket and valve stem seals but wanted to find out what else should be changed while I'm at it given the km's on the engine? I plan on re-seating the valves but didnt know if I should be changing the valve springs or valve guides or even the valves themselves just because...?
 

doc_rot

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Guides only need to be replaced if they are worn. The valve springs are probably OK as well but they are almost 40 years old. I usually replace them as it is cheap insurance against valve float and potential damage.
 

Tim

Administrator
Staff member
New springs and seals and you should be good for another 55,000km.

If you have a friendly machine shop, they could measure the guides to confirm.

Why are you doing a top-end rebuild? Oil leaks?

I did my BMW up a few years ago with a 1000cc kit from Siebenrock that included new forged pistons, new cylinders etc. and took the opportunity to replace the valves, springs, and guides. But mine were old and tired, and the new guides were a very small additional investment relative to the rest of the build.
 

ShadyOne

Member
Guides only need to be replaced if they are worn. The valve springs are probably OK as well but they are almost 40 years old. I usually replace them as it is cheap insurance against valve float and potential damage.
Thanks, I priced them up at only about $40 so pretty cheap.

New springs and seals and you should be good for another 55,000km.
If you have a friendly machine shop, they could measure the guides to confirm.
Why are you doing a top-end rebuild? Oil leaks?
I did my BMW up a few years ago with a 1000cc kit from Siebenrock that included new forged pistons, new cylinders etc. and took the opportunity to replace the valves, springs, and guides. But mine were old and tired, and the new guides were a very small additional investment relative to the rest of the build.
Looks like decision is made then...Is there any reason to replace rings too? At 135psi & 145psi there's plenty of compression.

The main reason I took the heads and cylinders off is to clean up the engine and paint it. Also the rear cylinder was fouling plugs and I wanted to investigate, I may have found the issue with a leaking valve stem seal, maybe....Or it may be the stupid single carb conversion kit ;)

Thanks again
 

Tim

Administrator
Staff member
The few times I've removed cylinders, I've always rebuilt with a fresh bore/pistons/rings.

Nothing wrong with making sure the pistons and cylinders are still in spec, and considering fresh rings and a DIY hone of the cylinders. 55,000KM isn't exactly low mileage.
 

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