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400F valve guides in a 350F

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Bryanj:
If you dont think exhausts need seals try a 750F2 with worn guides!

Orcade-Ian:
Hi Bryan,
So the mechanism of oil getting from the cam and valve gear top chamber and into the cylinder must be because the cam flings the oil at the side of the valve stem which then runs down onto the head of the exhaust valve when shut and then drops into the cylinder as it opens?  Is that what must be going on?  I hadn’t realised this was worse on some 750’s having never owned one (apart from a brief dalliance with a 750 FA (DOHC of course)

Ian

royhall:
Measured the 350 valves this morning.
Intake - 0.2160
Exhaust - 0.2152
Looks like using the Yamiya 400F guides would result in a 0.0005" increase in stem to guide clearance on the exhaust side, the inlets are the same. Doesn't sound a lot, will that be a problem in reality. Remember the 350 spec is without a stem seal and the Yamiya items have a stem seal, also it is on the exhaust side where a bit of oil is not as troublesome. I would prefer NOS items but cant even find a part number for the items with the stem seal let alone the actual guides.
I am undecided, are the Yamiya parts a Go or a No. Any views on the subject would be gratefully received.
Ian, thanks for your measuring service.

royhall:

--- Quote from: orcadian on May 20, 2019, 07:51:08 AM ---Hi Bryan,
So the mechanism of oil getting from the cam and valve gear top chamber and into the cylinder must be because the cam flings the oil at the side of the valve stem which then runs down onto the head of the exhaust valve when shut and then drops into the cylinder as it opens?  Is that what must be going on?  I hadn’t realised this was worse on some 750’s having never owned one (apart from a brief dalliance with a 750 FA (DOHC of course)

Ian

--- End quote ---
F2's have larger valves Ian. To get them in Honda changed the valve gear geometry that puts a side loading on the exhaust valve stems that leads to premature wear. The wear can be quite enormous letting oil run down the stems past the seal. I got Kibblewhite guides and valves for mine from CycleX in the states. They are supposed to mitigate the problem. Cant say it fixes it as that would need another geometry change.

K2-K6:
As Roy says,  the F2 used larger valves.  To get them into the combustion chamber without then being too close for the valve seats they pushed them up along the same axis and used piston shape to keep volume in size they needed.

It's not by much but places the top of valve stem higher too, resulting in the tappet geometry starting in more of an arc and producing higher sideways load.
In addition they reduced the oil drain routes in the head,  looks like they where trying to elevate the level to control wear. Plus an increase in fin size to cope with more heat. That raised level certainly seems to get them smoking when worn. It all goes to show how the original was just under the critical for wear as this small step really breaches it.
It all indicates that they were struggling with advancing the design by hitting limits imposed by original architecture,  probably a major contribution in going toward the 16valve successor to keep up with competitors or jump them.

Back to 350,  it looks like guides without seals have tight clearance because they get oil. With sealed guides needing more clearance to avoid problems from having the oil wiped from them.

Is that true from looking at it? In other words the two combinations do the same thing but have to be paired to work as intended.

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