Topic: When removing head, is replacing cylinder base gasket a must?

[fxef79]

I’d like to pull the head on a CB750 motor to check oil passages, perhaps valve lapping. Mainly because I need to pull the cam and towers and check the oil restrictors.

If you break loose the head, is it necessary to go all the way down to the base gasket, and this have to pull the cylinders, deal with pistons and rings, etc? 

Or, if you don’t break loose the cylinders can you just pull the head and then put it back on?


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[bryanj]

Some people sayno but i think if you have got the engine out, which is the hardest part, you would be peed off if you put it back in and the base O rings leaked plus everything is inthe gasket kit

[PeWe]

I have lifted head several times without changing base gasket.

But base gasket was not old and dry when done.  Maybe a year or max 2.
Can be different with old,  hard gasket and the 2 o-rings for oil feed.

If lifting the cylinder block you have opportunity to replace cam chain tensioner if rubber is hard and falling into pieces.
Finding more issues too

[fxef79]

Thank you.

I ask because doing this gets me into untrod territory (piston rings).

It’s not that it looks terribly difficult - it’s just one more new thing to learn that I’m not sure I’m ready for.


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[PeWe]

Typical for CB750 is worn exhaust guides. You will notice the play of valve when lifted 10mm without springs.
It should not be any play, maybe more like a softness sideways.

If bike has milage ( about +60000 km) there is a risk of a total head job by professional cutting the seats after guide replacements if needed.

And a rebore to next oversize pistons.
Check cruzinimage.net for cheap pistons.
This will end up in a good running bike.

My CB750 K2 runs fine with k7 +0.5mm pistons from cruzinimage.