350 Cylinder Differences

[rocketman]

O's and M's.  Odd or even years in a vin production code. I wonder if there is any correlation?  Mark.

[Bikenstein]

My spare set has beefed up flanges, pins and an O on the left cylinder, unlike Smokeys which has an O but no pins.

[steve]

Just caught up with the additional posts and have been surprised at how inconsistant the cylinder production appears to have been...obviously, alot depends upon whether or not the bikes mentioned still have their originals fitted. Thanks all for the posts...all very interesting stuff!

[old smokey]

Just looking at this thread as the GTR for sale in Random Lake seems to have pin cut-outs in the cylinders. I'm wondering if it's an early model that was titled as a '68...?

[Tom Meadows]

As Old Swartout noted, the pins through the cylinders are for noise damping, to help reduce that "ring" that makes two strokes a little noisy for some.You can achieve similar results by cutting 1/2" long pieces of 1/16" ID rubber vacuum tubing and pushing them between the cylinder fins, about four per row of fins at the corners, for total of 16 per barrel, which will make a noticeable difference in the sound.

I am guessing Bridgestone didn't think them worth the effort, or eliminated them for cost reasons.

My March of '73 GTO has no pins and has the cutouts in the side of the fins.



Tom

[BRT-GTR]

  Old Smokey,   There have been a number of threads on the pin/cut out subject :-

        http://bridgestonemotorcycleparts.com/index.php?topic=3159.msg16086#msg16086

   I think we can conclude that it is not possible to date a GTR/GTO from the presence or absence of the pins or cut outs in the barrels. The two features appear right through production on a completely random basis. Likeliest answer is there were at least two barrel suppliers, the Nippon Piston Ring Company possibly being one of them. BS used whatever type they had to hand.
   The only barrel feature that can be used for dating is the beefing up of the exhaust flanges which occurred after Serial No 21S01100, dated July 67 only a month after production started.

     Brian.

[BS Mechanic]

As a point of reference, the weak exhaust flange cylinders were still being used when my GTR was built, s/n 21T02281.  I am quite certain the cylinder are original as I purchased the bike new.

[slawsonb]

I am thinking that the theory of multiple suppliers is the only way to tie this story out.
...bert

[BRT-GTR]

Hi BS Mechanic,
                       Well, your post fouls up my previous suggestion that the exhaust flanges would have been beefed up at S/n 1100. The BS service bulletin, dated July 67, refers to the barrels being modified, I.E, shortened and the exhaust port reprofiled. It doesn't actually mention the exhaust flange change so maybe that happened later.  Anyone out there got a GTR in the vin range 1100 to 2281, please let us know whether it has the original weak flanges which are recessed at the back (like Bikenstien's picture, Page 1) or the strengthened flanges which are flared into the finning at the back.
   Thanks, Brian.

[slawsonb]

I expect the mixture (as I said earlier) is due to multiple suppliers and I should also have included loose inventory management.

...bert