BSA C25 motor

[dave higgins]

Just at the close of last season, i picked up a c25 scrambles bike cheap, it was lacking on compression & smoking a touch but the rest was a fairly tidy basis for a project build for another day.
Just for the hell of it, i rode it at the coombe martin meeting & was pleasantly surprised at how well it went, to be honest it pulled like a train & sounded sweet to.
This week i started pulling it apart & was shocked to see the damage inside, ( shocked because i new how much it was going to cost... ).
The valve guides were so worn that they were sliding up & down on the valve stems!!, the valves had elongated the seats, the piston had lost one of its clips & the gudeon pin was making its way out through the liner.
It looks like the pin has been quite happily chattering away on the liner for some time, you could put a penny in the groove & it would not foul the pistons movement & the rest of it was not that much better.....
Now as a mechanic of over 30 years sufference, i have seen some weird & wonderfull things, but i`ve never an engine seen so mechanically rough sound so sweet?.
I have said it before somewhere on the forum that some british engines were so crude that they would run on very wide tolerences & i think this bears this out. dave

[Peter Rotherham]

C.25 Engine.

Made at the evening of the BSA/Triumph Manufacturing Giant's life, these engines suffered from over development and poor materials. The Starfire/Barracuda/Fleetstar series all had undersized oilways that lead to premature wear. The last in the line, the Triumph Trophy/Trail Blazer and BSA 'Gold Star' 250's were better, but plagued by poor machining. I've worked with some of the machine tools that came out of Armoury Road, and to be quite honest they were totally worn out. The late Fred Barlow of FBS Norton fame who I worked with, often told me of "The bit of Wood" that was adjusted for each machining job. He was telling the truth.
That said, if left alone, these engines will run on, either sounding awful but being ok, or sounding ok but being awful, very much like Harley Davidson engines !
Todays CNC machines and better technology/materials can transform old British engines. The CCM engines were in essence the B.50's that had been breathed on in the BSA Comp Shop. For Scrambles, get some CCM innards into your C.25 and you'll have a sound motor.

[Andy Z]

Noise

Just at the close of last season, i picked up a c25 scrambles bike cheap, it was lacking on compression & smoking a touch but the rest was a fairly tidy basis for a project build for another day.
Just for the hell of it, i rode it at the coombe martin meeting & was pleasantly surprised at how well it went, to be honest it pulled like a train & sounded sweet to.
This week i started pulling it apart & was shocked to see the damage inside, ( shocked because i new how much it was going to cost... ).
The valve guides were so worn that they were sliding up & down on the valve stems!!, the valves had elongated the seats, the piston had lost one of its clips & the gudeon pin was making its way out through the liner.
It looks like the pin has been quite happily chattering away on the liner for some time, you could put a penny in the groove & it would not foul the pistons movement & the rest of it was not that much better.....
Now as a mechanic of over 30 years sufference, i have seen some weird & wonderfull things, but i`ve never an engine seen so mechanically rough sound so sweet?.
I have said it before somewhere on the forum that some british engines were so crude that they would run on very wide tolerences & i think this bears this out. dave

Interesting!
My mate had a Triumph TR25, with a totally rebuilt engine, and that sounded like a bag of bolts!

Having said that, I look after a firend's Honda NSR250, which started running on one cylinder all of a sudden, with no rattles or bangs. When I took that apart, the half the piston was missing in the front cylinder, a locating pin from the rings had fallen out and most of one of the rings was stuck in the exhaust port!

Good luck with the rebuild Dave,

Cheers,
Andrew

[Colin Sparrow]

They reckon that on the pre-war Mercedes Grand Prix cars drivers could tell if the crankshaft was about to break because they started to run more smoothly...

[druid]

Dave,
The C25/B25 has acquired a reputation as a hand grenade, unjustly in my opinion.
I've been campaigning a pair of B25s for the past 5 or so years in pre 65 scrambling. The only major problems in that time were a couple of big ends going, one because it was just worn out and the other because the oil filter collapsed and cut off the oil supply. Even then it was only £10 for a crank regrind and £8 for a set of shells ( same as Triumph twins).

They may have suffered at the hands of spotty youths thrashing them to death in the '60s but they last well for pre 65 and parts, both new and s/h are plentiful at reasonable prices.

Druid

[dave higgins]

Hi druid, yes i couldn`t agree more on what you are saying, its not one i`m going to rebuild at the minute as funds are low, i was merely commenting on how well the engine had done to run as well as it did with such severe internal injuries.
There is one thing you could enlighten me on though, the bottom ends shot & the rod & crank pin look the same as the earlier ss heavy roller type, i thought the c25`s had the shell bearings like you said, so what have i got????
Also the flywheels are a lot smaller than the c15 cranks, on the plus side some one had spent some time tuning it though as it was on 13.1 cr with a 72mm piston, so it was looked after at one point. terry weedy quoted £220 for an alpha pin & bearing fitted, so i`m thinking around £750 to rebuild it, which is means its gonna have to wait. dave.

[John-Boy]

Dave,
you might like to look at the NEB price list, whether or not you buy anything, it will give you an idea of the price of various racing components. Some of it is very expensive but other bits are reasonable.

http://www.joemaxwell-engineering.com/neb_pricelist.html

[John Wakefield]

Parts prices

Crazy prices, in the late 60's you could buy a genuine service exchange Villiers 32A re con crank shaft assy. for around £12-10-6 (old money.) C15 parts would have been at similar prices. Just popped into you local friendly dealer, & get one off the shelf by a storeman who new his stuff & did not need a computor to identify & find it in the stores. Happy days.

[dave higgins]

Yes john, but its now 2011, the storemans probably dead!! move on?