b25 engine rebuild

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b25 engine rebuild

Postby thingsthatgobang » Wed Oct 12, 2011 8:15 pm

Hi everyone I'm a new member and rebuilding a b25 ss motor. I have a keihin pwk 28 carb with base jet setting and manifold and will run boyer ignition and a high rise short megaphone like the b50 mx
I am going to clean up the ports and polish but other than the above the motor will be rebuilt as standard, Are there any other mods you can recommend for reliability or performance
for road use, Thanks in advance
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Re: b25 engine rebuild

Postby minetymenace » Wed Oct 12, 2011 8:38 pm

<135 to the forum thingsthatgobang.

thingsthatgobang wrote:Are there any other mods you can recommend for reliability or performance for road use,


A spare engine? Seriously they are great road bikes. Oil filter, and keep an eye on the pressure. Get the mixture right and if it pinks retard the ignition. Post pictures of the bike in project bikes and edit you profile to let us know roughly where in the world you are. Con rod can break if you thrash them.

PS deleted your duplicate post, just incase you wondered, I do that sort of thing now and again :grin:
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Re: b25 engine rebuild

Postby bossy » Thu Oct 13, 2011 11:11 am

As MM has noted above the Conrod is always going to be the main concern, they were a problem when the bikes were new and now they are 40 years old.

A new, much improved conrod from thunder engineering is £185. Thats a lot of money to replace something that isn't broke........yet. But IMHO it is a vital investment and will allow you to rev the nuts off it without worring about the engine exploding and taking your nuts off.

Irrespective of what you decide to do about the 'rod , lets have some pictures of the bike/project. We like pictures here.
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Re: b25 engine rebuild

Postby kommando » Thu Oct 13, 2011 1:09 pm

Make sure you fit Triumph 500 twin big end shells not BSA B25 ones. See thread on al/sn and whitemetal bearings.

Use sealent on all the threads of bolts and screws that access the oil ways eg sludge trap, non return valve etc. Make sure the pump sits on its mounting properly and that the pump does not leak. Use a good quality brand of garter seal in the inner timing cover eg pioneer.
Last edited by kommando on Fri Oct 14, 2011 7:17 pm, edited 2 times in total.
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Re: b25 engine rebuild

Postby B44R » Thu Oct 13, 2011 1:34 pm

2011_10130007.JPG


One that came in with a load of dead B25 engine bits I acqured 20 odd years ago for clutch and gearbox spares for my B44.
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Re: b25 engine rebuild

Postby thingsthatgobang » Thu Oct 13, 2011 9:26 pm

Thanks for your replies The Triumph 500 shells are they a direct replacement for the BSA one's . I'm still playing with the head at the moment so when there is something to take a picture of I will post some up.
All advise gratefully received
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Re: b25 engine rebuild

Postby HPbyStan » Fri Oct 14, 2011 2:36 am

thingsthatgobang wrote:Thanks for your replies The Triumph 500 shells are they a direct replacement for the BSA one's . I'm still playing with the head at the moment so when there is something to take a picture of I will post some up.
All advise gratefully received

YES
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Re: b25 engine rebuild

Postby Graham B » Wed Oct 19, 2011 2:15 pm

Just make sure the new shells have the oil hole :thumb
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Re: b25 engine rebuild

Postby HPbyStan » Wed Oct 19, 2011 6:56 pm

Graham B wrote:Just make sure the new shells have the oil hole :thumb


OR, don't use Castrol "R" and don't worry about it :-)
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Re: b25 engine rebuild

Postby beat » Wed Oct 19, 2011 8:52 pm

HPbyStan wrote:don't use Castrol "R"


O------------ N-----------

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Re: b25 engine rebuild

Postby backmarker1959 » Wed Oct 19, 2011 9:56 pm

your talking about Triumph and BSA shell bearings, but are there many genuine Triumph/ BSA bearings around , or are most copys?
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