Discussion in 'Help Wanted' started by Skankin_giant, Feb 8, 2012.
It shows up better on Nicks Piston.
Looks like I’m sorted and at about £3.40 a ring
I have to say that I broadly agree with Dave Reed; it's a rotten design, with no good purpose. Clearly the bridge is intended to keep the locating peg in place, but the thinned ring-ends are a substantial defficiency; they won't exert the required pressure on the cylinder wall and are inviting blow-by.
I would be removing the set-up completely, to be replaced by a round peg in the piston wall, plus straight cut rings notched to match. Being a stroker it is important that the rings are pegged, but this method is very poor indeed.
It was good enough for the Motorcycles so Im not going to go about changing it. I dont really want to go on messing about with the piston as where am I going to get another 3" Scott piston from?
That's interesting, as far as i recall Scotts own literature suggests 73mm as the standard bore.
Indeed it does but the actual is 78mm.
Yes that’s what Nick and I believed to be true, but after measuring the bore on my engine and the piston of Nicks it turns out to be 78mm.
I think Nick has mentioned before that the engines depicted in the sales info look almost pre-production due to the separate induction tube. I should think it would be near impossible to decipher the discrepancy between sales literature and the actual engines.
Edit - viewtopic.php?f=2&t=3182
I’ll post a picture with the Vernier Callipers in place when I get home.
So it would seem.....
I fell over my Verniers...
I think we've all done that at some point............ :lol:
Aldi's £9.00 a set and quite good quality.
Cheers for that Martin, will have a look, that was a Halfords Set, seemed ok, but I didnt really use them for any real engineering.
A highly accurate adjustable perhaps
That horrid peg and half ground away ring probably worked OK ish when the engine was new. I'd be willing to bet that the smallest amount of wear leads to exponential deterioration.
I agree that the Scott piston ring stop is an odd design but since it has proved satisfactory for many years in the motorcyles, there seems little reason to change it for stationary engine use.
Your point is taken though I'm not a great lover of the "eat s***, three trillion flies can't be wrong" argument
On a serious note have enough Scotts been run for long enough to demonstrate that the design is OK?
Nick, Is this statement based on recent knowledge?
Maybe this guy would be worth contacting www.mossengineering.co.uk
he seems to know a bit about Scott bikes. Interesting to note that he lists Phillip Daintree for Piston Rings so another avenue to follow.
I see no reason why the piston shouldnt be changed to pegs but I understand Steve's reluctance based on limited experience? or tools to do the job? I would have thought filing those rings by hand will be just as difficult as any variations in thickness could lead to other problems, which is the whole reason for replacing the rings in the first place, I guess.
Well, my father had his first Scott motorcycle in the 1950's and still runs a couple. As is the way with these things, I have seen the inside of quite a number (EDIT; perhaps they would be in pieces less frequently if they had proper ring stops!) and as far as I can remember, all the ally pistoned ones had that type of ring stop. I can't recall whether the earliest (1919) which has CI pistons was the same or not.
Yes, Roger Moss is quite a chap and has something of a reverence for all things Scott. I know he uses Silk pistons (as in George Silk rather than the fibre!) when available for his more sporty engines and I don't know what type of stops they have, but I haven't heard or read anyhting about changing the stops on 'normal' Scott pistons. ISTR there is a link on his site to the collected 'technicalities' from Yowl, the owners' club mag - a trawl through that would probably reveal if the ring stops have been known to give any trouble and, if so, suggested mods.
I’v ordered some rings from Otto Gas Engine Works over in the states, came in with the right angle and at a good price (6 for the price of 2 in the UK inc delivery).
I could possibly make a new peg, but why take the risk? I think I’m more capable at shaping the rings then producing a new peg with out making a hash off it! The biggest problem I would come up to is securing the peg to the piston.
I dont really like fiddling with something I cant get another of, I would rather take a few attempts at the rings then bugger the piston, rings cheap, 3” Scott piston....not so.
I know most of you gents have the capability to “improve” Mr Alfred Scott’s design, I have not, nor the will to do so.
This chap had some pistons adapted from blanks to suite a flat top flyer, seems they put a more conventual peg in.
http://flyingsquirrel.nl/technical/pist ... der-stubs/
The original rings are being replaced as I broke one....
Not sure it dates back that far (have to ask dad about the early one), if it came in with the ally pistons, we've probably got Harry Shackleton to thank.
Had a look at spare PAB piston and it has more conventional peg type stops, probably screwed in as there is a thickened region inside the piston under each stop. Would there be enough meat to do the same on the SE piston? I wouldn't want to be the one to find out there wasn't!
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