Bridgestone Motorcycle Parts Discussion Board
Bridgestone Tech Talk => 350 Talk => Topic started by: gtrman on December 10, 2015, 06:37:37 PM
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Mine were beyond staying in the flywheel recess so i had a machinist put screws like the Kawasaki Samurai. Finally after this and nikasil!! I've got it together. Anyone know what year a na1 4900 engine relates to? 1967? Need western high handle bars and shocks.
Cheers mates... Doug
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Doug,
The engine numbers can be a couple of hundred either side of the Vin plate number. It's the letter in front of the Vin number that dates the bike production, IE, 21 ? 04793. Would suggest yours was made late 67 or early 68. Let us know the Vin letter and we can pin it down.
Did you take a photo of the crank seal screws, would like to see that. Did something similar myself back in the day using 3mm countersunk screws and a hand held electric drill. Not the most accurate job but it worked and the seals stayed in. ;D
Brian.
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Brian,
What do you think of peening the outside seal to the chrankshaft in, say, four places? What about high temperature adhesive alone or coupled with the peening? Make any sense?
- Bob
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Hey Bob that's similar to what I did on both my GTR engine rebuilds, centre punch marks around the circumference of the recess holding the seal in tight.
Z
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Hi Bob, (must learn to type faster, Zs post came in while writing)
Not quite at that stage yet but I've been thinking along the same lines. This topic comes up on a regular basis. I will install the crank seals, despite the early problems. BS retained the seals during production and somehow redesigned the crank recesses after 21F5701 to 'ensure positive retention'. Not sure what they did, made them deeper or increased the interference fit tolerance ? I don't know. I do have cranks (both corroded) before and after this number, I'll have a closer look whenever I get them cleaned up and stripped.
Adhesive - I'm sure there are products available that would work but would have to be chosen carefully. Surface preparation would also be critical for long term bonding.
Peening - I think this is the option I will be using. As you suggest, maybe 4 centre punch dots on the flywheel face around the outer edge of the seal, 1- 1.5 mm back from the edge. This should push metal towards the seal lip and form small nibs to keep it in. What do you think.
From experience, I can tell you that should the seals come loose, you can hear them rattling with the engine on tickover. That saved me an expensive barrel replacement on one occasion but I may just have got lucky.
Brian.
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I thought the conventional wisdom was that the seals are not required. I don't want to beat this to death (maybe it has already been), but I am not planning to use the seals. What is the main motivation to use them?
...bert
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Bridgestone removed them due to the problems with them coming loose, then changed their mind and put them back in. One would have to assume that meant there were problems when they were removed. My guess is that there were problems with adequate connecting rod big end lubrication when run at high speed for extended time. The seals direct lube to the rod bearings through the center of the crankpin in lieu of the more common practice of slotted rod journals to get lube to the bearings. They probably were OK during normal riding, leading the factory to initially assume they would be OK without the seals, then they started getting reports of some failures and re-instated the seals.
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Thanks Brian... Vin 21 Z 048xx...engineNA1 049xx the machinist took pics ill try to get that. He used two counter sunk screws each side. I wanted three but he builds racing engines so im confident hes right about it..
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Im sure running without resulted in high oil consumption and poor fuel mileage... For racing it wouldn't matter...Doug
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Running without seals has no impact on oil delivery, that's determined by the oil metering pump. Oil consumption is not changed at all, so mileage is also unaffected.
My personal belief is that it was marketing that dictated the crank seals, not engineering. They sound like a good idea in the advertising, but I doubt they really accomplished much. Crank bearing failure is not really a common failure, and no other 2 stroke manufacturer chose to go with seals. Mine never came loose, but when I had my crank rebuilt by BS, I chose to leave them out.
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They arent seals actually. They are retainers to trap oil and lube the outer bearings otherwise oil will go straight through an go up in smoke...the way i see it anyway
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Kawasaki Avenger had these too. It was also a twin rotary valve engine. But i agree it seems a bit odd tthis design. Wether effective or not. Service bulletin reversed decusion to leave them out though...why?
Someone copied from the other manufacturer maybe. I have a racing engine in my spare parts no seals on the crank.
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Interesting to hear Kawasaki used them.
Sure wish we could go back in time and ask some questions of the original BS design team!
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Well i found a taka 100 ;D pros????? cons????? Should i go for it... i all ready have 10 bikes,,, watts one more ::) and it has the paper too..... ;D allso it only has 817 miles on it... ;D
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WoW....talk about a left turn. :o
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Always signal your turns, helps others know where you're headed! ;D
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Left turn Clyde - or was that right turn Clyde ??
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Yes i agree. Need to go back in time..but somebody knows for sure. Im certain there are Japanese collectors with this knowledge.
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Its in Bend so that has to be close to you. Buy it to ride on the coast, they are a fun bike...DL
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I am inclined to believe the re-instatement of the seals was from engineering, not marketing. Do we have any evidence that the these seals were marketed as an advantage? It's fun talking about this, but Steve Reed would probable say stop talking and start working! He told me the Kaw triple design migrated from Bridgestone to Kawasaki, so that's where the Kaw seals may have come from. Just learned that the H1 handle grips were the same design and it looks like, from appearnace, that the H1 has the same grab bar as the 350. We may want to look closer at early '70's Kawasakis for 350 adaptable parts.
The usefulness and attachment techniques of these seals really needs to be tested rigoursly and long term to determine their advantage. Maybe the road race guys could shed some light on this. Anyways, its fun to try to stay as OEM as possible.
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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.
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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
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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.
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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
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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.
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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
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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.
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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...
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Did the kawi triple have rotary valves? Thought it was old piston port technology, although awesome power just the same.
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Not rotary or reed. you're right, piston port that would snap your neck. ;D
...bert