400F valve guides in a 350F

[royhall]

Is it okay to use a set of 400F valve guides in a 350F. Are the valves the same diameter stem etc. Am struggling to find 350F exhaust guides that have the stem seal and would like to use this set from Yamiya   http://www.yamiya750.com/index.php?main_page=product_info&cPath=179_273_180_186&products_id=3630   Alternatively, does anyone know of a source for the stem seal guides. Many thanks again.

[royhall]

Anyone got a micrometer and a pair of 400F valves. Can you measure the stems please. Cheers.

[Orcade-Ian]

Hi Roy,
I have a complete 400 head so I will pull a couple of valves,  1 in, 1 ex and measure the unworn bit just below the collet groove with a mic.  Might not be until tomorrow though - a few glasses of wine may have put me under the affluence of incahol and I have to walk a straight line out to the workshop.

Ian

[royhall]

Thanks Ian your a star. Hope your Mikes in real money not that god awful French crap that needs converting to the real world. Hic Hic

[Orcade-Ian]

I can measure them in imperial, metric or Orkney strides, whichever you wish.

Ian

[royhall]

feet and inches please.

[Orcade-Ian]

Hi Roy,
Just sneaked out to the toy cupboard and pulled a couple of valves from this old head.
Measured just above the wear mark near to the collet groove:

Inlet 0.2160”

Exhaust 0.2155”

Looking in my Cycleserve manual that tallies with their table within a few tenths of a thou.

Stems are virtually the same figures where they have been in the guides.

Strange but this spare head has only got seals on the inlet side whereas the heads on both my 400’s and the 350 have seals on all valves.  Is there ever enough overlap to warrant a seal on the positive pressure exhaust side?  Perhaps the seal on the exhaust side just holds enough oil in there to prevent the valve drying up in the guide?

Ian

[royhall]

Thanks Ian, I shall cross check the 350 valves tomorrow. They are the sizes for the 400 valves, thought I had better double check. Cheers Roy.

[Trigger]

Different size guides 

400 Four EX stem is 5.477
              IN stem is 5.480

[Orcade-Ian]

Hi Roy,
Yes the sizes I have given are 400 valves. 

Trig (and Roy)

Not sure where the Cycleserve info has been culled from (published Sept 1975 with permission from Honda and thanks given)
The valve stems are indeed half a thou different with the exhaust the smaller.
However, the service limit is the same for both at 5.35mm (sorry Roy, 0.2106}

These figures for the 350 are all identical to the 400 in this same manual

[ Guests cannot view attachments ]

400 info above


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350 info above

Ian

[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]

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

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.