Author Topic: GTR crank seals  (Read 6973 times)

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Offline BRT-GTR

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Re: GTR crank seals
« Reply #20 on: December 16, 2015, 12:35:44 PM »
     I'm jumping back a bit on this post.
       Karl, it's my understanding that removal of the crank seals was a field fix only. There were a number of Service letters from Rockfords to dealers stating that they should be removed when servicing and a credit would only be given for the work when the broken or removed seals were returned to Rockfords !!. Failure of the seal probably only came to light when they broke up and went up the ports taking out an expensive barrel and piston, so would have cost BS or Rockfords a lot of money.  I think one letter stated that the seal failure rate was 3% but I suspect it may have been higher. They certainly didn't want the buying public to know about this fault and kept it low key. I have never seen an official service letter reversing the seal removal fix.
      I would be surprised if any engines came out of the factory with the seals omitted, unless someone can tell us otherwise.
    
     So, I suggest BS believed the seals were performing a valid function and continued to fit them at the factory. From the 'Oil injection system' drawing in the manual, in theory they should help guide the oil through the flywheel drilling to the big end but just how effective they were is anyones guess. The drawing indicates a solid flow of oil into the back of the disc valve, through the outer bearing and flywheel to the big end which would be true for a high pressure fed 4stroke motor. As the BS pump only dribbles oil into the cases I suspect this positive flow never occurred. Anyway, as you say, the oil got to all the bearings and generally they don't give trouble, so the oil supply worked one way or another.

      I've often noticed a degree of cross fertilisation between BS and Kawasaki and the guy I took my GTR cases to for vapour blasting (who is a Kawa triples rebuilder), immediately asked me which kawasaki model they were off, some similarity there.  Kz 550/650 points & condensers also interchange with the GTR/GTO.   They both started bike production at about the same time in the early 60s and were fighting for a share of the market and with each other. Did they both recruit design engineers from failing companies like Meguro or more likely Tohatsu or did they simply use the same suppliers. I'm sure a bit of industrial espionage and copying went on, if one thought the other was gaining a lead. Kawasaki copying BS ?, I like to think so. It's possible some of the BS engineers went tp Kawasaki when BS pulled out of bike production. What do others think?.

   Brian.
« Last Edit: December 16, 2015, 12:43:29 PM by BRT-GTR »
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Offline slawsonb

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Re: GTR crank seals
« Reply #21 on: December 16, 2015, 12:45:23 PM »
When I first rebuilt my 350 in 1974, upon disassembly I discovered it had no seals (21S01306/NA1-01329) at 14K miles. It must have been rebuilt prior to my ownership. I put it back together with no seals and ran it another 13K miles with no failures of any engine internals. Perhaps since we will not be able to test this we could also evaluate members experience with engine longevity with and with out seals. Then stir that in with any racing experience.
...bert

Offline BS Mechanic

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Re: GTR crank seals
« Reply #22 on: December 16, 2015, 03:08:46 PM »
I have no direct evidence on reasoning behind the seals, it's just fun to speculate so late after the fact!  My guess is based on my own experiences as a design engineer and dealing with marketing and sales people.  Engineers don't typically like to included features that offer small benefits, and have a high risk of catastrophic damage.

I do distinctly remember seeing a very nicely done poster at the Cedar Falls IA Bridgestone dealer extolling the virtues of the 350's oil injection system, showing how the oil is directed to the main bearings first, before flowing past the "seals" or better "shields" and then on to the rod and cylinders.  All two stroke manufacturers were at that time trying to overcome a poor reputation for reliability due to lubrication issues.  One of the ways they did this was by trying to show that the new oil systems were like a four stroke, with pressure lubricated bearings.

I also remember that at the time I attended the Bridgestone training program in Rockford their recommendation was to remove the seals if the engine was opened for any reason to eliminate the very real threat of severe damage if a seal came loose.  It happened enough to make the guys at Rockford pretty gun shy about the seals.  Apparently that direction was changed later, but I didn't have any later contact with the Rockford people.

Offline slawsonb

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Re: GTR crank seals
« Reply #23 on: December 16, 2015, 04:06:10 PM »
My guess is based on my own experiences as a design engineer and dealing with marketing and sales people.  Engineers don't typically like to included features that offer small benefits, and have a high risk of catastrophic damage.
I couldn't agree with this comment more, although I have spent an inordinate amount of time talking marketing types out of offering features with potential negative consequences. Guess that's why engineers stick together. ;D
...bert

Offline davis

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Re: GTR crank seals
« Reply #24 on: December 16, 2015, 07:46:58 PM »
Okay, this thread stimulated a closer look at the manual. I definitely see the design intent now. Oil is introduced to the outside of the outboard bearings, through them to an annular volume enclosed by the seal. The seal keeps oil from being slung out and around the crank, encouraging flow through the piston pin to feed the big end bearing and center crank bearings. The theory seems sound. Apparently not necessary under normal use as testified by Bert. I've been exposed to about eight cranks now and all nonrusted bearings remain pretty smooth and tight. All-in-all, I'm impressed with the crank bearing design which must have receive sufficient lubrication.

Offline slawsonb

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Re: GTR crank seals
« Reply #25 on: December 17, 2015, 11:57:48 AM »
The lubrication of the big ends without the seals may be more accident or serendipity than anything else. As someone said earlier, without the ability to consult the designers we'll just have to speculate (fun huh?).
...bert

Offline Gerrit

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Re: GTR crank seals
« Reply #26 on: December 17, 2015, 05:16:24 PM »
The original rods don't have slots in the big-ends and personally I'd prefer rods with slotted big-ends. Having said that, the original Kawasaki S series rods didn't have slots either and engine lubrication did not include direct oil feed to the big-ends as on the H series so as long as the oil pump works and a good quality oil is used I don't see any harm in running without the end seals.

Offline gtrman

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Re: GTR crank seals
« Reply #27 on: December 19, 2015, 06:09:50 PM »
I concur with your observation...i think those oil retainers are necessary unless running premix. Mine won't fall out now...they are screwed in place hehe just like the kawasaki A7 of this period.

Great advice here...

Offline gtrman

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Re: GTR crank seals
« Reply #28 on: December 19, 2015, 06:13:55 PM »
Did the kawi triple have rotary valves? Thought it was old piston port technology, although awesome power just the same.

Offline slawsonb

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Re: GTR crank seals
« Reply #29 on: December 19, 2015, 07:23:05 PM »
Not rotary or reed. you're right, piston port that would snap your neck. ;D
...bert

 


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