GTR crank seals

[gtrman]

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

[BRT-GTR]

    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.
           Brian.

[davis]

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

[ziggy stardust]

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

[BRT-GTR]

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.

[slawsonb]

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

[OldSwartout]

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.

[gtrman]

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..

[gtrman]

Im sure running without resulted in high oil consumption and poor fuel mileage... For racing it wouldn't matter...Doug

[BS Mechanic]

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.

[gtrman]

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

[gtrman]

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.

[BS Mechanic]

Interesting to hear Kawasaki used them. 

Sure wish we could go back in time and ask some questions of the original BS design team!

[srpackrat49]

Well i found a taka 100   pros??  cons?? Should i go for it... i all ready have 10 bikes,,, watts one more   and it has the paper too.....   allso it only has 817 miles on it...

[moonpup]

WoW....talk about a left turn. 

[BS Mechanic]

Always signal your turns, helps others know where you're headed!

[dcr]

Left turn Clyde - or was that right turn Clyde ??

[gtrman]

Yes i agree. Need to go back in time..but somebody knows for sure. Im certain there are Japanese collectors with this knowledge.

[Mopar392]

Its in Bend so that has to be close to you. Buy it to ride on the coast, they are a fun bike...DL

[davis]

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.