Author Topic: valve stem oil seals, cb340/4  (Read 787 times)

Offline dickyta2

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valve stem oil seals, cb340/4
« on: July 17, 2018, 09:17:03 PM »
Has anyone had any issues with aftermarket valve stem oil seals?

   I`ve just rebuilt a 350/4 motor, including new pistons and a rebore  and I`m getting smoke coming out of the breather pipe and a small amount out of the exhaust...it does seem to be running fairly well though!!!

Offline Trigger

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Re: valve stem oil seals, cb340/4
« Reply #1 on: July 17, 2018, 09:41:52 PM »
It is most probably not smoke, it is oil vapour from the oil cooking because it is hot

Offline dickyta2

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Re: valve stem oil seals, cb340/4
« Reply #2 on: July 18, 2018, 10:22:17 PM »
Okeydokey, cheers for that Trigger :-)

Offline Trigger

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Re: valve stem oil seals, cb340/4
« Reply #3 on: July 18, 2018, 10:42:15 PM »
Your engine breather hose should go to your air box. If it is not vapour maybe, someone did not rebore your barrels to the correct spec.

Offline dickyta2

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Re: valve stem oil seals, cb340/4
« Reply #4 on: July 19, 2018, 08:43:33 PM »
Theres no airbox on it I`m afraid!!

Offline royhall

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Re: valve stem oil seals, cb340/4
« Reply #5 on: July 20, 2018, 10:08:51 AM »
Not all 350/4's had valve stem oil seals on the exhaust side, just taper top guides. On the exhaust side the pressure in the port tends to push the oil back up the valve stem so it's unlikely to be the exhaust side. Seals are fitted to the intake as the suction of the descending piston pulls the oil down the stems so if one is displaced or worn out the engine will burn oil and cause smoke. Hope that makes sense. That said, stem seals won't be the cause of vapour from the breather hose that's usually crankcase pressurisation from worn bores or a bad rebore. Or as Trigger says overheating engine, if your running pods you may be way too lean and that will cause the overheating.
« Last Edit: July 20, 2018, 10:10:38 AM by royhall »
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Offline Bryanj

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Re: valve stem oil seals, cb340/4
« Reply #6 on: July 20, 2018, 06:08:51 PM »
Always got vapour but not liquid from 500 and exhaust guides gone gives clouds of blue smoke

Offline royhall

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Re: valve stem oil seals, cb340/4
« Reply #7 on: July 20, 2018, 06:36:40 PM »
Always got vapour but not liquid from 500 and exhaust guides gone gives clouds of blue smoke
As Bryan says if your guides are shot you will get smoke regardless of seals or not. But I am assuming they were checked when you rebuilt the engine. The CB750F2 as an example is notorious for knackered smokey exhaust guides. How many miles has it done since the rebuild?
Current bikes:
TriBsa CCM 350 Twin
Honda CB350F in Candy Bacchus Olive
Honda CB750F2 in Candy Apple Red
Triumph Trident 660 in Black/White
Triumph T100C
Suzuki GS1000HC
Honda CB450K0 Black Bomber
Honda CB750K5 in Planet Blue Metallic (Current Project)

 

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