BSA Owners' Club Workshop Discussions

The BSA Workshop => Twins => Topic started by: mandy [s] on 03 Mar, 2026, 21:32

Title: Plunger frame
Post by: mandy [s] on 03 Mar, 2026, 21:32
Hi all thought we would start on this, any ideas why the back wheel sits so high of the ground, when of the stand the the frame has a ground clearance of 5 inch from under the front two frame tubes, could the plunger units be seized,been sat for over 40 years.
Title: Re: Plunger frame
Post by: V500 on 03 Mar, 2026, 22:06
More like the wrong stand I would say.
If you think the plungers might be seized then bounce the rear of the frame on the ground and see if there's any movement.
Title: Re: Plunger frame
Post by: DAVE BRADY on 03 Mar, 2026, 22:18
Hi,

The springs look right for the wheel being at the bottom of the suspension travel - top spring extended and lower spring compressed.
Is the stand on back to front?

Dave.
Title: Re: Plunger frame
Post by: limeyrob on 03 Mar, 2026, 22:22
The plungers look right. The stand may be too long but that's odd because its quite a specific type.  The fork rake looks odd (could be a trick of the photo?), has that frame been modified?
Can you post a photo of it on its wheels?
Title: Re: Plunger frame
Post by: DAVE BRADY on 04 Mar, 2026, 09:27
Hi,

If you look at the feet on the stand they are on edge when they should be sitting fully on the ground. On this '51 Flash the rear wheel is about 4" off the ground.  Another possibility is that the 'stops' that limit the movement of the stand have been repaired and too much weld has been applied.  Carefully reducing the stops will lower the back end but do it gradually as a littler bit of material removed has a big affect. 

Dave.
Title: Re: Plunger frame
Post by: V500 on 04 Mar, 2026, 09:37
Fair point, but that said the centre stand in the pic looks to be at a good angle, and not nearly vertical as some repaired ones are.
Title: Re: Plunger frame
Post by: mandy [s] on 04 Mar, 2026, 18:59
Few more pics, thanks for the replies so far.
Title: Re: Plunger frame
Post by: mandy [s] on 04 Mar, 2026, 20:24
here is a few more pics thanks for the replies,
Title: Re: Plunger frame
Post by: Daz on 04 Mar, 2026, 20:58
I think that frame has been hacked about.
(https://cybermotorcycle.com/gallery/bsa-frames/images/BSA-Frame-a7-a10-spring-frame.jpg)
Title: Re: Plunger frame
Post by: limeyrob on 05 Mar, 2026, 09:39
I'm thinking the same, the rake looks wrong.  I think the stand is right.
Title: Re: Plunger frame
Post by: mandy [s] on 05 Mar, 2026, 17:21
Quote from: limeyrob on 05 Mar, 2026, 09:39 I'm thinking the same, the rake looks wrong.  I think the stand is right.
hi, we did renew all the headstock bearings inside the frame and headstock was all smooth no signs of weld or rough metal or join welds,no signs of smooth filler around the stock, I know it has some non original parts, just have to go with the rebuild and see what it looks like.
Title: Re: Plunger frame
Post by: mandy [s] on 05 Mar, 2026, 17:30
Quote from: V500 on 04 Mar, 2026, 09:37 Fair point, but that said the centre stand in the pic looks to be at a good angle, and not nearly vertical as some repaired ones are.
hi, I have posted a pic with the tape measure showing hight from ground, note the center stand hangs low  and will not pull up anymore, this is with the bike on its two wheels.
Title: Re: Plunger frame
Post by: Gup holland on 05 Mar, 2026, 17:43
Hello mandy , i have also a 1951 golden flash.
On the stand there is prox 40 mm under the tire. Center of rear axle is 370mm. Center of bolt footrest is 265mm on the right side.
If you doubt the rake , measure the wheelbase.

Gr gup

I tried to upload pictures, it was denied?????  Wrong file???
Title: Re: Plunger frame
Post by: DAVE BRADY on 05 Mar, 2026, 20:56
Hi,

It looks like the rear section has been extended. Look at the relationship between the line of the top tube and the rear frame sloping down to the plunger units.  Also, the distance between the plunger units and the frame down tube - this looks longer hence the wheel sits higher when on the main stand.

Dave. 
Title: Re: Plunger frame
Post by: limeyrob on 05 Mar, 2026, 22:04
"It looks like the rear section has been extended."  You could be right, I was focussing on the front but the line from the head stock to the rear top tube is much straighter on the frame than on the plan.
Title: Re: Plunger frame
Post by: DAVE BRADY on 05 Mar, 2026, 23:45
Hi,

I would guess that the idea would be to make a longer wheel base lowrider/bobber.

Dave.
Title: Re: Plunger frame
Post by: mandy [s] on 06 Mar, 2026, 09:02
Thanks, I can see from the pics of the diagram what you mean, I suppose I go with it or would a standard rear bolt on frame bring it back in line
Title: Re: Plunger frame
Post by: limeyrob on 06 Mar, 2026, 09:27
Build as a "special" for now, a lot of parts will be common and you don't need to get every part right so long as it looks good. It may turn out nice and be a bit different.
Title: Re: Plunger frame
Post by: mandy [s] on 07 Mar, 2026, 09:07
Thanks, good idea, will carry on see how it turns out.