Bridgestone Motorcycle Parts Discussion Board
Bridgestone Tech Talk => 350 Talk => Topic started by: Kenneth Pagel on June 12, 2017, 10:04:05 PM
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I've just read an old thread regarding the 350 crankshaft end seals that says it's just fine to run without them. (Service bulletin BSG-0070) I have very low mileage 1967 GTR that I'll be restoring shortly. This bike started and idled after sitting over 30 years when I acquired it. It does put out white smoke from the rh muffler, and was told this is due to bad rotary valve seals, and not the labyrinth seal. My question is do I need to remove the crankshaft end seals due to the age of the motor to prevent possible distintegration and risking blocked oil passages? The motor is still mostly together;only the carbs and clutch have been removed. Thanks in advance!
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Smoke from the right side is nearly always caused by a failed crankshaft seal, behind the primary drive gear. It can be replaced in the bike by removing the right side transmission cover. The seal is housed in the rotary valve cover, at least that's my memory! Shop manual shows details.
I have seen no indication that the seals improve engine life. My personal belief is that they were added not by engineering, but by marketing who at that time were trying to get out from under the poor reliability view many held about two stroke engines.
The seals do occasionally come loose, and can cause catastrophic damage.
So in my view, there is little to no benefit, traded against the very real potential to destroy a good engine!
Simple choice, at least for me at the time. I'm not sure I'd take an otherwise sound engine apart just to remove the seals though. That's a harder choice, but based on the potential harm, "probably" best.
My 350, purchased by new in 1968 had the seals for 45K miles, till a main bearing cage disintegrated (unrelated to the seals). When I had Rockford rebuild the crank (1972) they removed the seals. The engine now has about 60K miles, still with no other issues.
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nysz1b,
Whoever told you about the smokin right cylinder may not have been fully familiar with the GTR engine/crank construction. To clarify :-
The title of this Topic refers to 2 special 57mm seals that BS installed on the outer cheek of the outer crank flywheels, one either side. Theoretically, these 'encouraged' the injected oil to flow towards the big end bearings, whether they were ever effective is debatable. As BS Mechanic states above, they sometimes come loose, break up, and get sucked into the barrel ports !! It does require a full engine strip to remove them but can be done without pressing the crank apart. It's your choice. I'm leaving mine in but will peen the outer edge to improve retention.
The seal that is likely causing the over oiling is set into the R/H disc valve cover, where the crank passes through and stops oil from the primary drive case being sucked into the right cylinder, again as stated above. (The left cylinder is not affected by this issue). My GTO has a similar smoky right cylinder. As far as I can assess this is the only potential source of additional oil to the right Cyl. Although an incorrect fuel mixture or poor combustion may also cause a smoky cylinder. Correctly set up, the 350 oil pump cannot send more oil to one cyl than the other, so can be ignored at this stage.
The labyrinth seal referred to is in the centre of the crank and separates the two cylinders. Of all metal construction, it should never wear unless the adjacent crank bearings fail.
Hope this helps, Brian
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BS friends
Rockford, years ago determined and recommended that those end seals 09090-117 be removed
or left out when ever one rebuilds a 350 engine
Hope this helps
Richard Clark
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Good to know, just leave them out
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Thanks for all the feedback!
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Kawasaki had them fastened in place with three screws. No trouble. I did mine this way, but with two screws. They aren't really seals. They retain oil for the bearings..so they are oil retainers. I'd load a picture if i could of mine, but i cant seem to browse my folders.
That BS service bulletin was retracted i think.
Doug