Author Topic: BS90 Scored Barrel  (Read 266 times)

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Offline pafiat

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BS90 Scored Barrel
« on: April 01, 2020, 05:16:18 AM »
Hi, I'm a new visitor here. I have aquired most of a BS90 sport. I have removed the head and barrel to see what horrors lurk inside. Among other problems, the barrel is lightly scored. I understand from the Internet that the barrel surface is hard chromed. Can this barrel somehow be repaired and re-used. If not, how are people getting their sports back on the road?
Regards Pat

Offline Jeff Bar

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Re: BS90 Scored Barrel
« Reply #1 on: April 01, 2020, 04:16:36 PM »
You can have the cylinder re-chromed, but it usually  costs less to just buy a new one. Jeff Bar

Offline rwgibbon

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Re: BS90 Scored Barrel
« Reply #2 on: April 03, 2020, 01:07:52 PM »
I agree with Jeff. It may be cheaper to buy a NOS barrel.

Good luck, enjoy, and take pictures.

Stay healthy

Randy

Offline pafiat

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Re: BS90 Scored Barrel
« Reply #3 on: April 05, 2020, 10:53:06 PM »
Hi, thanks for the advice. Looks like Richard might have both the alloy and cast iron cylinders in stock. Any advice on advantages/problems with either? I don't have enough of this bike to make a pristine example so going for a period racer type look so something that can be tuned/ported would be good. An alternative is a 100 cylinder, is it a direct bolt-on to the 90 motor, they are the same stroke and I need a new head anyway as the current one has been attacked by several blacksmiths and is pretty much toast.
Rgds Pat (I'm in Australia)

Online BS Mechanic

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Re: BS90 Scored Barrel
« Reply #4 on: April 05, 2020, 11:07:19 PM »
Back in the day, I bought a 90 sport with a damaged bore and piston.  To save money I replaced the alloy cylinder with a cheaper cast iron one.  The cast iron one probably won't last as long, doesn't cool as well, and needs a bit larger clearance as I recall to avoid scoring if it gets too hot. The cast iron bore worked just fine for me.  As I remember I put about 10,000 miles on the iron barrel with no problems. 

Be absolutely sure you use chrome piston rings if you go with a cast iron bore, or the rings will wear faster.  Conversely, if you go with an aluminum/chrome bore, DON"T use chrome, as chrome on chrome is very bad combination.

Offline OldSwartout

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Re: BS90 Scored Barrel
« Reply #5 on: April 06, 2020, 08:41:43 AM »
The pistons for the iron and alloy cylinders are different. The one for aluminum has a higher expansion rate to match the cylinder.  As BS Mechanic said, if you reuse it in the iron cylinder it needs about an extra .001-.0015 in. clearance. It would be a little noisy when cold, OK hot. If  you can buy a new correct piston to go with an iron cylinder, that would be better.

I'm not sure the 100 cylinder is a bolt-on. On the 175 (same bore as 90), the 200 cylinders (same bore as the 100), won't fit because the spigot is too large to fit into the crankcase.
Karl Swartout
Mooresville, IN
BS175 Roadracer. BS200RS, BS175HS
BS350 GTR

Offline RayK

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Re: BS90 Scored Barrel
« Reply #6 on: April 30, 2020, 06:01:38 PM »
Pat from Australia
Your inbox is Full. You have replies from myself as well as Richard Clark backed up.
RayK.
Australia
BS 175DT, BS 50 Sport x 1, BS 90 Mountain x 3, BS 90 Deluxe, BS 90 Sport x1, BS 60 Sport, BS 90 Trail, BS100 Sport.

Offline paul

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Re: BS90 Scored Barrel
« Reply #7 on: May 02, 2020, 07:11:19 AM »

I remember a BS dealer back in the 1970 s that bored out a 90 iron cylinder and used a bigger piston from another Japanese bike, transforming it into a BS 120 cc

Offline pafiat

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Re: BS90 Scored Barrel
« Reply #8 on: May 04, 2020, 05:51:11 AM »
Hi RayK, thanks for the alert. I think I have deleted stuff in the inbox. Only one message I could find, would that fill up the inbox or do I need to look deeper somewhere? I'm keen to be part of this forum so please bear with me while I become familiar with it. Rgds, Pat

 


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