TR6 TR6 Motor Question

[glemon]

OK, actually it is a TR250 Motor question, but still the 2.5 liter Triumph straight six.

I was pursuing a change from a single roller cam timing chain to a double roller on my TR250 engine, figuring the double roller is a reliability upgrade (the single does look a little wimpy).

I acquired the double roller cam sprocket from a later TR6 Motor, and then a double roller crank sprocket at a swap meet with a bunch of Triumph parts. The Double roller is the same outside diameter as the single, but when I went to put it on I discovered the I.D. is mabe 1/4" too small.

Did they change the crank from single roller to double, or do I simply have the wrong sprocket? I put the engine back together with the single, but I am still thinking about going to the double roller and since I haven't installed the motor yet shouldn't be that hard to switch if all I need is a different sprocket, I am not going to pull the crank and have it machined down at this point though.

Thanks in advance. Greg

Thanks,

 

[SpitBang]

Hi Greg,

I am afraid I cannot answer why you are finding different size, but I upgraded my '72 GT6 from single to duplex chains with no problems regarding crank diameter. So I don't think it necessarily has anything to do with changing from single to duplex chains.

 

[SpitBang]

Oh, and if it is any help, I have just put a micrometer round my crankshaft, where the sprocket would go, it measures 1.376"
How does that compare with your sprocket internal diameter?

 

[glemon]

That does help, my crank measures 1.37" my sprocket is 1.12" inside diameter, I think I have the wrong sprocket--oh well was free, maybe will try to scare up a new one or good used from a TR6 and see if it works, Greg