[Thomas]

I checked the part numbers again. The list contains three different pistons for 1937 and I presume it is part number 13664 for my 500cc Model 9 (not really sure).

[Thomas]

OK, I understand! Then my only option is to wait until my piston is worn and then go with it and the barrel to a respective workshop. I am a bit surprised that there is no initiative in the club. I am no expert and no mechanic but I am sure that certain workshops can easily make a batch for different Sunbeams.

[wessex_man]

Hi Thomas the pistons that were made ten years back were not made by the club but someone who needed a piston so he had a batch made just one piston type (model 9 27-35). He made the surplus availble to other beam users. I don't know how many had to be made. I do know he used old pistons to measure and reverse engineer that one.

[Thomas]

Yes, W_Man, it might be somthing for an autojumble. But as you say, after 100 years... hm. That's the reason why I talk about pistons made for the club (as about ten years ago). Earlier or later everybody will run into the problem to get a new piston. Instead of having the fuzz with letting one or more made (still waiting for drawings from the club) I would prefer to get a ready one, of course. I don't know the part number and I still have the original standard bore (and would look for an oversize one).
Cheers, Thomas

[wessex_man]

Russ That explains the dullness. Yes you can do alot to bring an old piston back to life to get you back on the road. For example if the ring grooves are worn they can be re-cut and oversize rings be fitted.

For all your information currently I see there is a 250 Sunbeam piston on Ebay and a series 2 350cc OHV New old stock if anyone's interested including the Lurkers. This source is loosing momentum because of the rule changes this year there have be fewer listings.

Thomas at the moment it's a case of looking through autojumble stock and getting lucky. As I asked before do you have the part number and your current bore size. It's really a question of what you can get and sometimes you may have to overbore to suit the piston that you can find.

You have got to remember these machines are fast nearing 100 years old. I doubt the makers would have thought they would be still in use today and long may there use continue.

[Russ]

the picture of my dull piston is a Heplex 3051 (5809) by as you say Hepworth & Grandage (Graces Guide) this was a NOS Piston which I had to get rejuvenated as it must have been left in a damp environment as the Gudgeon pin was rusted solid and there were bits of broken piston ring rusted in the Ring grooves....but it was brought back to life easily enough and with the new Turner & Cox supplied rings and oil scrapper fit a treat and will definitely address my issue as there is considerably more compression on kicking over......unfortunately I haven't managed to get the old girl out on the road for her maiden voyage as I managed to crack the exhaust downpipe which is off being repaired fingers crossed I'll get it back early next week.....one thing I will check though is that the Crankcase breather non return valve is assembled in the correct order

[wessex_man]

Thomas explanation of oval ground. If you measure across the bottom of your piston across the gudgen pin then at 90 degrees you will find a difference in diameter in the order of 0.005'. Indicating that it has been oval ground. The piston is also taper ground from the bottom of your oil ring to the bottom of the piston (skirt).

Re the series two piston It's larger diameter than the pre 1935 Model 9's so the ones which were made a few years back by Sean would not have been any good for you. I don't have any more information on these.

Russ your piston is a Model 9. The number inside the pistion is a casting number not the finished item. This is A Hepworth and Gradidge No5809 Sunbeam 500 OHV Type C

Thomas yes you are right not any old piston will do for using a modified piston. I got one of the Norton ones modified for 1929-35 beams when Martin Bratbuy did pistons and have modified two since. They fall in between the 9 and 90 preformance wise and you have to fit a 1mm spacer under the barrel and adjust the push rod lengths.

Whats also needed is a mechanical archive even if the piston as reference is worn. Piston castings are bigger and normally diecast rather than investment cast and a pattern would need to be made. Hence why I said the tooling would be expensive.



 

[Thomas]

BTW: Can you explain this?

...when you consider most of the originals were cylindrically ground and are slightly oval by design.

[Thomas]

I would say pistons are of interest (normal and oversize) as requested. For example, I am looking for a first oversize for my 1937 Model 9. I mean, this is an old issue in the club. And before asking how much everybody is willing to pay we better find a company and the prices for the job. Modifying a piston is an interesting idea but at least I have no clue what could be possible for us and especially for the final workshop. I can't bring them ANY piston, right? So, if you have an idea then describe it in detail for those without a lathe... My request is somewhat desperate because the club delivers no solution athough we will all run into need of new pistons at a certain point. I know that about ten years ago pistons were available in different sizes. But nothing since then.

[wessex_man]

Interesting thread some thoughts. Which Model pistons would be of interest? What level oversize? I had difficulty in selling a couple of brand new Model 8's pistons a few years back if you look back. How much would people be prepared to pay for one? Even before you consider the range of stock which would have to be held for the range of models.

Tooling for a one off/ low volume  is very expensive especially when you consider most of the originals were cylindrically ground and are slightly oval by design.

I've been looking at the issue for model 9/90's up to 1935 for a while.

In part you can modify an obtainable new piston for far less than trying to get the real thing. Speaking with experience the WD Norton 16H can be modified sucessfuly. Ok +40 will get you standard bore beam (79mm +40  gives you near enough 80mm). You have to machine the skirt so the conrod clears, valve pockets and slightly re-profile the crown. There is enough meat on the crown to do this. Weight wise it's within 10 grams of the original so balance isn't an issue. Having said that even the oversized Nortons are becoming harder to source.

[Daniel]

I would be interested too into a piston.

[Thomas]

Ok, Graham, how can I get them?

[shorrog]

Hi Thomas
We do have a few drawings and they may be of use.
Graham

[Russ]

I'm in for a 1927/28 Model 9 +.040" & a +.060" (with valve cutouts) if they're going to make any the picture of the dull piston is one I had not sure if it's an original I'm sure it is the picture of the shiny piston is a batch that Sean Kelly (Sunbeamland) had made many moons ago it has a slipper type cutout for the Gudgeon pin and Circlip....perhaps I should ask him if he still retains any drawings.....he may well have sent an original to get copied

[Thomas]

As there have been no (oversize) pistons for years, one can have them made in specialised workshops. Are there any piston drawings in the club?