4bl (3mb0?) cylinder with a 3bn head?
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What cylinder is currently on the engine? If it’s a 3BN then that is the only cylinder you have can fit without adding a later crank...
It doesn’t matter what the engine and head have stamped on them, just the current barrel that is running on the bike... -
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@Bavarian are you sure it says 3DD and not 3DB? Because only the first year dt125r was 3DB and after that it was 3RN1, 3RN2, 3RN3 etc up to 1996. The early 3DB had a bore of 56.4mm and stroke 50.0mm. after that they were bore 56.0mm and stroke 50.7mm so if you have the early one you'd think it would be quite hard to come by for a used one as it's a one year only item, but that same early cylinder of 56.4/50.0 was used in the tzr125 up to 1996 so that would make it a lot easier to find searching for tzr125 1988-96 cylinder.
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You would only be down on compression. The real problem would be putting a 3bn barrel on a later engine because the stroke of the crank/piston would be longer than the barrel and smack into the head...
The 3bn barrel wasn’t even a whole year model was it? My 1988 DTR125 has a 3mb barrel and crank...
Didn’t the TZR use 3mb barrels? I know I’ve used the TZR pistons in my 3mb Dtr as oversized. I’m not well versed in the history...
I wonder it the ‘R’ was for revised? Definitely wasn’t for race!...
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@Bavarian I just looked your VIN up on Yamaha France and your bike is 100% an early 3DD1 model (sold as a 3BN in the UK); 56.4 x 50.0mm bore and stroke, VM26SS round slide carb and different electrics including a separate YPVS controller on top of the airbox.
So if you were going to fit a later crankshaft and cylinder you might end up needing a TM28SS flatslide carb and different stator, loom and CDI unit to fully convert it. Is your original cylinder serviceable?
Take a look here: https://www.yamaha-motor.eu/fr/fr/service-maintenance/parts-catalogue/#/
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I would like to add my 2 cent's.I have 3MB and 2RH(=3BN) cylinders,I've measured them off the bike and on the 3BN00 cases from my 4BL bike,and everything is the same,I think on '88 DT's and early TZR the less 0.7mm is on the crankcase side not the cylinder..
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@MadGyver obviously the .7mm difference in stroke would be acquired by altering the crankshaft as that's the only possible way to alter the stroke, but you're saying they both use the exact same cylinder dimensions? Did you measure the port heights because that is where we'd see these possible differences?
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@markus-w I had put the cylinder of a TZR125 2RH on my DTR,complete with piston using the DT's stock base gasket,did not mount the head.I wanted to take measurements to make a custom gasket in case I was going the TZR way and not the Athena170. Everything aligned like the stock,piston bdp was same level with the ports floor and at tdp was level with the cylinder.Put it out and started measuring the height of the cylinder and was the same with my 3MB and the Athena. Didn't do a full port map.
@Calum I didn't have 2RH crankcases to do the reverse measuring.I assumed that the 0.7 is from the cases.
I had the belief like everyone that was from the cylinder. -
Thanks everyone! That's very useful information for me.
@MadGyver so does that mean 3MB will possibly work on 3BN engine with shorter stroke?
Perhaps the difference on the stroke comes from the connecting rod? Could that 0.7mm difference in stroke cause a significant performance drop?My barrel still has some life in it although it has been resleeved and sleeve quality doesn't look that good. But I want to buy another one for spare and to play with
It seems it's quite difficult to find a 3BN one.
