Author Topic: BS50 Sport iron cylinder  (Read 320 times)

0 Members and 1 Guest are viewing this topic.

Offline CL-100

  • Trade Count: (0)
  • Expert Registered Bridgestone Member
  • ****
  • Posts: 325
  • CL-100
BS50 Sport iron cylinder
« on: October 28, 2021, 03:04:04 PM »
I'm in the process of getting set up to start a full restoration on a BS50 Sport.  The bike was thought to be a runner, although I was never able to get it started.  I spent some time trying to figure out what wasn't working and I found that I was only getting an intermittent and weak spark so I just packed the bike away and bought a new coil and ignition parts that went into the storage bin for that bike.  I recently pulled the cylinder off with an intent to send it out for a fresh bore to accommodate the first-over(0.25) piston I already had.  The machine shop cautioned me that a first-over bore might not clean up the cylinder enough if there was existing damage.  Well, as it turns out, there is some damage (see attached pictures). 
What really caught my attention is that the area between cylinder bore and the transfer port opposite the exhaust seem to be real close.  I put a digital caliper on it and it measures about 1.7mm at the thinnest part of the skirt.  The farther you go down the skirt, toward the top of the cylinder as it's laying upside down, the thicker it gets. 

Also, on the photo with the burnt and scarred piston you can see that both rings look to have a shiny appearance.  It was my understanding that the iron cylinder used a chrome plated top ring and an iron bottom ring.  Both rings look the same to me. 

So my first concern is whether or not the cylinder is suitable for a rebore, assuming I can find a second-over (0.50) piston and rings.  Secondly, is the damage to the piston and bore from someone installing the wrong rings on this piston?

Any thoughts out there from anyone with iron cylinder experience is appreciated.  Thanks.

 

Offline Chibi62

  • Trade Count: (0)
  • Full Bridgestone Member
  • ***
  • Posts: 79
  • Retired USAF E-9 Combat Veteran / F-16, A-10, F-15
Re: BS50 Sport iron cylinder
« Reply #1 on: October 29, 2021, 11:57:33 AM »
I have had a similar cylinder condition successfully bored. From what I'm seeing with yours the level of damage on the bore wall would indicate a decent amount of material needs to be removed. It appears to me your likely to get into trouble with the cylinder port thickness. Not knowing what your machine shop will charge you. I suppose it's worth a shot to have it bored up to the point the damage is removed. Otherwise you might be better off looking for a good used cylinder. It's a coin toss .. Your machinist should be able to definitely say yes or no ..

As for possible mismatched rings. I have unknowing used wrong rings in a few applications. Bikes ran well with no real issues. I'm seeing chrome rings here in a iron cylinder. From the pictures it appears the cylinder was seizing due to lack of lubrication. Check the piston for signs of the wrist pin starting to scuff & seize. That is another sign is was ran dry ..   

Kevin
   
« Last Edit: October 29, 2021, 12:01:33 PM by Chibi62 »

Offline OldSwartout

  • Global Moderator
  • Trade Count: (0)
  • *******
  • Posts: 1247
Re: BS50 Sport iron cylinder
« Reply #2 on: October 29, 2021, 07:26:13 PM »
I agree with Kevin, definitely ran without lube for a short time.  Wrong rings won't cause that, only chrome rings on a chrome bore will. Iron rings or chrome are OK in an iron bore.

IHMO, the 0.25 over piston will work. The serious damage is all below the transfer ports, so if it doesn't totally clean up, it won't hurt performance. The rings will seal properly above the ports. There could be some long term effect on piston and ring longevity, but you probably won't put 15-20,000 miles on it, so no worries.

Karl
« Last Edit: October 29, 2021, 07:28:43 PM by OldSwartout »
Karl Swartout
Mooresville, IN
BS175 Roadracer. BS200RS, BS175HS
BS350 GTR

Offline CL-100

  • Trade Count: (0)
  • Expert Registered Bridgestone Member
  • ****
  • Posts: 325
  • CL-100
Re: BS50 Sport iron cylinder
« Reply #3 on: October 30, 2021, 06:42:44 AM »
Kevin and Karl, thanks for your responses.  Since I'm at the beginning end of this project, I'll spend some time looking for replacement parts first.  I'm hopeful but not optimistic I'll find a 0.50 second-over piston and rings or even a good used cylinder.  At least I have an option of trying the first-over bore.  I'm not likely to put more than 20 miles a year on it.  I've always been partial to the little Sport 50's and 60's so I'm determined to make this work. 

Rowland

Offline Chibi62

  • Trade Count: (0)
  • Full Bridgestone Member
  • ***
  • Posts: 79
  • Retired USAF E-9 Combat Veteran / F-16, A-10, F-15
Re: BS50 Sport iron cylinder
« Reply #4 on: November 05, 2021, 09:21:48 AM »
I also wanted to mention that when you see a recess hole on the top of the piston (see picture) indicates it's intended for use on a iron wall cylinder. A piston with a "swirl mark" on the dome of the piston indicates use in a chrome bore cylinder.

Under most applications. The upper ring is chrome (compression) while the bottom ring is Iron (for oil sweep). In race motors it's not uncommon to remove the lower iron ring, and run the engine with only the upper chrome ring.

Kevin     

Offline CL-100

  • Trade Count: (0)
  • Expert Registered Bridgestone Member
  • ****
  • Posts: 325
  • CL-100
Re: BS50 Sport iron cylinder
« Reply #5 on: November 05, 2021, 05:35:45 PM »
I did not know that the recess hole in the top of the piston indicated that it was for an iron wall cylinder.  I appreciate the lesson as well as the  information on the purpose of the two piston rings. 

Thanks!

 


Gallery


Views:18
Comments (0)
By: Steve Swan

Views:46
Comments (0)
By: rwgibbon

Views:39
Comments (0)
By: rwgibbon

Views:51
Comments (0)
By: rwgibbon

Classifieds

one pair new 8435-9000 speedo/tach cushions
Price: $70.00
Date: 12/07/2021 11:50 pm
Time Left:
BS-7S/Surfrider piston rings and parts needed
Date: 12/03/2021 11:58 am
Time Left:
Need used rear spokes for BS 175. Three outer and One Inner. Any help greatly appreaciated
Date: 12/01/2021 01:08 pm
Time Left:
Need Hurricane 175 air tubes and front mud flap
Date: 12/01/2021 09:22 am
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