The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: jachenbach on 12.05. 2015 23:42

Title: Wristpin too long??????
Post by: jachenbach on 12.05. 2015 23:42
Started assembling the top end for the Golden Road Super Star. New Hepolite piston kits (std bore), newly sleeved cylinders. Piston to cylinder clearance? Check, good. Ring end gap? A bit tight, filed for .008" clearance. Installed right piston on rod, all good. Left piston, what the hell????? Wristpin doesn't go in far enough to install circlip. Looks like its up against circlip on the other side. Warm it up, remove wristpin and measure wristpin length and distance between circlip grooves. Not a great measurement, but wristpin looks to be about .010" too long! Make sure everything is clean (again), oil wristpin, heat piston, try to install (not on engine). Yup, the wristpin is too long, by just an rch more than the width of the circlip groove.
  So............. Anyone have an idea what kind of tolerance I should allow for? I'm guessing this is not real critical, but I've never had to do this before.
  Also, a while back, someone had a sleeve slip down. Seems to me it would be easy enough to drill and tap a hole in the cylinder skirt, dimple the liner, install a grub screw and grind it flush. The case mouth would prevent the grub screw backing out and the liner couldn't move. Worth doing or is this too rare a failure mode to worry about? Got these cylinders already sleeved with a truckload of parts, so don't have any idea who did the work.
Title: Re: Wristpin too long??????
Post by: wilko on 13.05. 2015 00:21
Just get it ground down to length.
Title: Re: Wristpin too long??????
Post by: Butch (cb) on 13.05. 2015 13:02
Yeah – But I think the question here is what should that length actually really be? Same as the one on the others side you might presume. If you have confidence that that one is really right, maybe it is short by the 10 thou that this one is long? Or maybe send it back to the supplier for a replacement.
Title: Re: Wristpin too long??????
Post by: Derby Rob on 13.05. 2015 19:26
only looked at this post because i had never heard of a "wrist pin" .....now i know
Title: Re: Wristpin too long??????
Post by: Butch (cb) on 13.05. 2015 22:32
Indeed - 'gudgeon' to you and I.
Title: Re: Wristpin too long??????
Post by: jachenbach on 14.05. 2015 03:30
Oops, sorry. English bike, guess I should use English terminology. Yes, gudgeon pin. And I'll use my spanners to assemble it (we call them wrenches in the USA).  *smile*
Title: Re: Wristpin too long??????
Post by: wardleybob on 14.05. 2015 19:37
Hi I would send them back hepolit is now wassells !
Title: Re: Wristpin too long??????
Post by: Triton Thrasher on 14.05. 2015 19:49
They've sent you a wrong pin.

They're not supposed to be too long!

What does the seller say?
Title: Re: Wristpin too long??????
Post by: jachenbach on 15.05. 2015 03:12
I got these with the truckload of parts from which I'm assembling bikes. They were probably bought by the previous owner about 25 or 30 years ago. The box says $28.95 and contained 2 pistons with rings, circlips and wristpins (sorry, gudgeon pins). I'm going to take it in to work and try to turn it down on a lathe. If the cutters won't cut it, I'll use a grinder.
Title: Re: Wristpin too long??????
Post by: duTch on 15.05. 2015 04:38

use the grinder with it spinning in the lathe- steady steady like
Title: Re: Wristpin too long??????
Post by: Triton Thrasher on 15.05. 2015 06:45
Those will be British Hepolite then.

Put a chamfer on the end of the shortened pin, same as original.  Not tapered inside, are they?
Title: Re: Wristpin too long??????
Post by: Butch (cb) on 15.05. 2015 08:52
Yes, it will surely need to be ground - I don't think a cutter will touch it. Best to take the one from the other side as a pattern for size I guess.
Title: Re: Wristpin too long??????
Post by: chaterlea25 on 15.05. 2015 10:13
Hi All,
The pins will machine down in a lathe if the correct tool inserts are used
I chamfered a couple recently without trouble
I scored a box of tips for very hard materials on fleabay for €20 inc post
I was able to machine down a bearing outer diamater with them *eek*

HTH
John
Title: Re: Wristpin too long??????
Post by: edboy on 15.05. 2015 10:34
could it be an a65 gudgeon pin?. i would use an old a10 one as they very rarely wear unless corroded.
Title: Re: Wristpin too long??????
Post by: jachenbach on 15.05. 2015 13:10
Darn it , edboy, why didn't I think of that????? More than likely have others, I'll have to look. Hate it when I miss the obvious.
Title: Re: Wristpin too long??????
Post by: jachenbach on 17.05. 2015 23:10
Well, I measured several wristpins (gudgeon pins) and all were the same length, so went ahead and ground one down by .020" and piston is now mounted on connecting rod, circlip in it's groove. All well and good until I started to lower the barrels on........... Huh????
Where are the cylinder base studs? Only have 3 on this case. Looked through parts boxes, none there. Guess I'll order studs, nuts and washers before proceeding. Oh well, plenty of other work to be done in the meantime. Need some other odds and ends anyway (clutch adjusting screw, gearbox inspection plate screws, mainshaft) so may as well start putting a parts order together (again). Making progress, but slow. Don't know these bikes well enough (or at all, really) to plan ahead. Just dealing with one thing at a time. Funny thing is, I'm really enjoying it, rather than getting frustrated. With the frame painted, forks and wheels mounted, engine/trans in the frame, it's starting to look like a bike!
Title: Re: Wristpin too long??????
Post by: duTch on 18.05. 2015 00:22
 
Was thinking that A65 piston pin would be a bit longer, but no matter- jobs done... *smile*

 When ordering barrel flange studs, keep length in mind (obvious to some, but easily overlooked) that there's thin flange barrels too, I got slightly longer ones, as I wasn't happy with what I had- can't recall detail without digging for the info
Title: Re: Wristpin too long??????
Post by: Butch (cb) on 18.05. 2015 11:22
I had the same thing putting my H1 (a K – sorry) together from boxes of bits. A gradual process of working on different areas, looking through the boxes and then sourcing what couldn’t be found. I very much enjoyed the process up until I started the bike for the first time (about 18 months in). After that it ceased to be a pleasing project to while away time against and was just another bloody bike that didn’t work properly.