Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: llessur on December 31, 2016, 06:15:55 PM
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Set about overhauling the engine today, and on the strip down I was surprised to only find four valve stem oil seals on the inlet valves i.e. nothing on the exhaust. I looked at the parts manual and this seems to confirm this. I would be grateful if you could let me know if I am missing something. Thanks and all the best for the New Year
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Some valve guides require stem seals and some don't.
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Many thanks, all the best
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Lots of engines only have seals on the inlets and the main reason is that during the inlet phase when the piston is descending there is a negative pressure within the cylinder and with a worn guide oil can be sucked into the cylinder to be burned with the fuel. On the exhaust side, the piston is ascending when the valve is open, creating a positive pressure to force the gases out so no oil can enter via the guide. The small amount of overlap with the valve timing when both valves are open together is usually considered negligible. Many accountants know about this and delete the seal on the exhaust side.
Ee, the nights are fair drawin' out now tha knows!
Ian
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That makes sense- thanks. What originally through me was that I had downloaded the Workshop Manual from this site and it shows eight seals, however on checking the parts manual it only shows four.
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That makes sense- thanks. What originally through me was that I had downloaded the Workshop Manual from this site and it shows eight seals, however on checking the parts manual it only shows four.
I noticed that too. It is in the 350 section of the manual though, although it says nothing different in the 400 section.
I had a look in the Haynes manual; that says the seals are only on the inlet valves.
Final clue was in the 350 Parts List. Early models (prior to a given engine number) had 8 seals, after that only 4 were used.
So as Orcadian says the inscrutable Japanese accountants possibly decided to save a few Yen and deleted the seals on the exhaust valves.
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That makes sense- thanks. What originally through me was that I had downloaded the Workshop Manual from this site and it shows eight seals, however on checking the parts manual it only shows four.
I noticed that too. It is in the 350 section of the manual though, although it says nothing different in the 400 section.
I had a look in the Haynes manual; that says the seals are only on the inlet valves.
Final clue was in the 350 Parts List. Early models (prior to a given engine number) had 8 seals, after that only 4 were used.
So as Orcadian says the inscrutable Japanese accountants possibly decided to save a few Yen and deleted the seals on the exhaust valves.
Not deleted Chris, upgraded from 4 seals to 8 seals. All the early engines never had the seals on the exhaust valve guides, even on the 750's.
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Not deleted Chris, upgraded from 4 seals to 8 seals. All the early engines never had the seals on the exhaust valve guides, even on the 750's.
That's not how I understand it from the Parts List Trig.
This is the text from the 350/4 Parts List:
[attachimg=1]
So up to engine number 1068969 there were 8 seals (for inlets and exhausts) then from engine number 1068970 there were only 4 (inlets only).
Not sure what the 2000000 series engine numbers are, a different market maybe?
The 400/4 Parts List also only lists 4 (inlets only).
I'm presuming that the 350 manual was put together in the early days which is why the diagram text shows 8 seals.
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Not deleted Chris, upgraded from 4 seals to 8 seals. All the early engines never had the seals on the exhaust valve guides, even on the 750's.
That's not how I understand it from the Parts List Trig.
This is the text from the 350/4 Parts List:
(Attachment Link)
So up to engine number 1068969 there were 8 seals (for inlets and exhausts) then from engine number 1068970 there were only 4 (inlets only).
Not sure what the 2000000 series engine numbers are, a different market maybe?
The 400/4 Parts List also only lists 4 (inlets only).
I'm presuming that the 350 manual was put together in the early days which is why the diagram text shows 8 seals.
So the 350 f0 has 8 seals and the f1 has only four, does anyone know how many 350s were made?
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Just looked at the Parts list again in case I had missed something (I had ....).
Quantities in the left column are for the F (F0?), those in the right are for F1.
So it looks as if F engine numbers were 106xxxx, F1 were 200xxxx.
Not sure if that actually helps though!
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My f is 1012587. engine 603