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Re: 728cc sprinter/hill climber

You've just got to watch you don't do the same thing as the B44/B50's and start breaking gears. It sounds like the 250cc is being reliable as it is, it's a tricky one, more power without breaking things..!

Did you up-grade the oil pump? I've read in Rupert Ratio's book that the later pump can be fitted to the earlier engine with a bit of machining. I'm going to see if SRM or someone does a better pump for my 1970 bike.

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

I realise you have a different use for your B25 Nig, I just wondered if you'd had any experience with road gearing for them.

I wish I knew what I was talking about too Ron :-)

email (option): horror@blueyonder.co.uk

Re: 728cc sprinter/hill climber

looking at the original gearing for my 1968 TR250, this was 16 X 49 - pretty low.

Your 54mph @ 4000 rpm in 4th - equates to 81mph @ 6000rpm, my guess would be something like 80mph @ 7000 to 8000rpm would be more like.

As i say, i'm about to put my B25 onto a friends inertia dyno, mainly to get a base BHP but also to sort out my ignition/carb problems I've had all year.
I have the option on a 90x70 B44 motor for next year MX or Bonneville and need to get a handle on the b25 problems.

One thing about this type of dyno is that it can usefully predict road speeds for a given BHP

Re: 728cc sprinter/hill climber

looking at the original gearing for my 1968 TR250, this was 16 X 49 - pretty low.

Your 54mph @ 4000 rpm in 4th - equates to 81mph @ 6000rpm, my guess would be something like 80mph @ 7000 to 8000rpm would be more like.

As i say, i'm about to put my B25 onto a friends inertia dyno, mainly to get a base BHP but also to sort out my ignition/carb problems I've had all year.
I have the option on a 90x70 B44 motor for next year MX or Bonneville and need to get a handle on the b25 problems.

One thing about this type of dyno is that it can usefully predict road speeds for a given BHP

Re: 728cc sprinter/hill climber

Torque my friend is the killer - that lovely feeling we enjoy when you wide open big single - and that sinking feeling as it skips gears, as the teeth fall off!

The bottom end has been re-built as per E-V's article on B50 forum, the con-rod is a billet jobby, bought cheap as it was one of a pair for a Daytona.
The rod is a problem area, a trident or later daytona rod will fit, but depending one the year of the crank (mines 1969) you may need to machine the inside of the (removable) flywheels for clearance.
You also need better quality shell bearings, mine are NOS early triumph twin - lead/iridium types - the standard ones are soft and crush out of tolerance when revved.

Re oil-pump - yes mine is one the three bolt cast-iron jobbies, ended up bidding and winning (on Ebay) three pumps which where on at same time - priced from £70 down to £21 !!!
I waited a few weeks until none where listed and sold two of them for more than what i bought the 3 for - tee hee.
Make sure you get the higher output pump, not all CI/3-bolt pumps have a higher output - i think they are marked VC or something, i was able to strip and check which was which.

In my cases, i didn't need to do any grinding of the crankcases - 1970 cases shouldn't need machining either.

One thing i have picked up and will be fitting is a 1970 onward inner-case (cam side) - this has provision for an oil-pressure switch, i'm fitting a 20psi from some car or other connected to a warning light.

Make sure you fit a new crankshaft end oil-seal, that the end of he crank isn't bell'ed and that is is smooth and well lub'ed when you fit the inner case.

Re: 728cc sprinter/hill climber

HORROR - email me again please, managed to delete your email rather than passing to my PC for viewing ......

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