Author Topic: 1966 Sport 90 piston/cylinder swap?  (Read 3313 times)

0 Members and 1 Guest are viewing this topic.

superspin1

  • Guest
  • Trade Count: (0)
1966 Sport 90 piston/cylinder swap?
« on: March 12, 2016, 08:22:42 PM »
My 1966 Sport 90 has a bad piston/cylinder. The Sport 90 had aluminum cylinders with chrome plated bores I believe. Is it possible to swap a cast iron 90 cylinder/piston assy like from a Mountain 90 onto the Sport 90 engine? Or, maybe even a TMX 100 piston/cylinder? Just looking at options here and wondering if other 90 Sport owners had run into this situation and what they did? Any help/information on the subject would be greatly appreciated. Thanks!

mqtsteve

  • Guest
  • Trade Count: (0)
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #1 on: March 13, 2016, 07:18:11 AM »
The aluminum cylinder bore from the 90 sport can be re-chrome plated.  There are several companies that do plating.  There's probably one near you (there are other threads about platers).  You could put the cast iron cylinder, piston and rings on it.  If you do, you should also change the cylinder studs, head studs and head gasket.  Download a parts manual to figure out the parts needed.  The 100 TMX parts will NOT fit the BS90.  The parts should be available from Richard(site owner) or on eBay.  Good luck with your project, Steve

Offline BS Mechanic

  • Trade Count: (0)
  • Expert Registered Bridgestone Member
  • ****
  • Posts: 278
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #2 on: March 13, 2016, 09:51:04 PM »
I did the aluminum to cast iron swap on a 90 I bought cheap because it's cylinder was bad.  This was about 1969, and it was a cheap solution.  As I remember, the cast iron cylinder was about $15!  No one had any idea where to get the aluminum cylinder fixed, and a new one was off the chart for a poor college student at that time.

It was an easy swap, but not necessarily the best solution in todays world. 

I would definitely check with one of the cylinder repair places first to see if it can be fixed.

Offline disc_valve

  • Trade Count: (0)
  • Expert Registered Bridgestone Member
  • ****
  • Posts: 406
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #3 on: March 14, 2016, 07:08:23 AM »
Hi,

the cast iron cylinder is a straight swap for the alloy one, and if you buy a used cylinder it will come with the right head studs anyway, I'm not sure that you need to change the cylinder base studs, though. I built a spare engine for my 90 staring with a knackered bottom end from a 90 Sport, end fitted a 90 Deluxe top end onto it. It seemed to fit OK. One extra thing you will need to change, though, is the Exhaust Clamp nut - the alloy cylinder has an internal thread, whilst the cast-iron  one has an external thread. Also, the Exhaust pipes are different part numbers - I'm not sure what the difference is, though. It may be a different bend angle or maybe slight difference in length. I guess that's a case of try it and see.

Graham

Offline OldSwartout

  • Global Moderator
  • Trade Count: (0)
  • *******
  • Posts: 1251
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #4 on: March 14, 2016, 08:49:13 AM »
Make certain you use the piston for the cast iron cylinder as you said. There will be an issue if you use the piston from the alloy cylinder in the cast iron cylinder.  The pistons have a different coefficient of expansion and the one for the aluminum cylinder may tighten up in the cast iron cylinder at operating temperature unless you build in slightly more clearance than recommended. There is about .0015 in. difference in cylinder bore growth between the two cylinders from room temp. to operating temp.
« Last Edit: March 14, 2016, 08:51:03 AM by OldSwartout »
Karl Swartout
Mooresville, IN
BS175 Roadracer. BS200RS, BS175HS
BS350 GTR

superspin1

  • Guest
  • Trade Count: (0)
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #5 on: March 14, 2016, 11:59:11 PM »
Thanks all, I have a line on a Mountain 90 cylinder but condition is unknown at this time. I don't think the original aluminum cylinder can be saved due to the deep 360 degree gouging. I'm thinking at this point a usable cast iron cylinder/piston is going to be the least expensive way to go. I'm hoping I can utilize my stock muffler and get away with just swapping the head pipes between the two? I will know more once I get the cast iron cylinder in hand. I really appreciate all your help and input (and I will probably have more questions as I proceed)...:)

Offline slawsonb

  • Trade Count: (0)
  • Master Registered Bridgestone Member
  • *****
  • Posts: 1398
Re: 1966 Sport 90 piston/cylinder swap?
« Reply #6 on: March 15, 2016, 11:30:02 AM »
I have had cylinders repaired (welded) to fix large chunks missing around the exhaust ports of a 350 cylinder. They weld them up, machine and hone, and replate (in this case with nicasil). Pretty severe damage can be fixed. If you send pics to one of the shops that specialize in these fixes, they can give you a quick idea of your cylinder's repairability.
...bert

 


Gallery


Views:299
Comments (0)
By: Steve Swan

Views:286
Comments (0)
By: rwgibbon

Views:259
Comments (0)
By: rwgibbon

Views:294
Comments (0)
By: rwgibbon

Classifieds

Gtr Gto rear grab rail
Date: 01/17/2022 08:15 am
Time Left:
Mud flap wanted
Date: 12/29/2021 08:31 pm
Time Left:
175 Dual Twin Wanted

Date: 12/24/2021 09:44 am
Time Left:
BS 90 Front Brake Lever
Date: 12/17/2021 12:26 pm
Time Left:

Recent Downloads added

BS200 Mk II RS & MK II SS Exclusive Parts
Rating: (None)
Filesize: 358.29KB
Date: March 07, 2021, 07:30:10 PM
1970 sales brochure
Rating: *****
Filesize: 6753.33KB
Date: July 16, 2020, 10:01:18 PM
2018 Article in Motorcycle Classics
Rating: (None)
Filesize: 3877.88KB
Date: June 29, 2020, 05:26:00 PM
350 GTR pdf version

Rating: *****
Filesize: 7366.26KB
Date: March 14, 2020, 09:41:23 AM

Powered by EzPortal