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General => Douglas Motorcycles - General Discussion => Topic started by: Red on 10 Jan 2022 at 11:58

Title: Pistons
Post by: Red on 10 Jan 2022 at 11:58
I have perhaps foolishly volunteered to try and sort out a stock of old pistons that the club still has. I am told they have been stored away for several decades and I need to try and identify what engines they will fit. Sadly some are in a poor condition but could still be useable. I have a copy of the page from the Heplolite catalogue shown in the posting below, but does anyone have anything better or something that may cover some of the earlier models. Also can anyone identify any of the following Hepolite part numbers. Any help will be appreciated  https://www.douglasmotorcycles.net/index.php?topic=8989.0. Thanks

Roy

9747
4870
1600
9749
5788
Title: Re: Pistons
Post by: EW-Ron on 10 Jan 2022 at 20:51
If the numbers can't identify them, a pic and some basic dimensions might ?
The bore size and gudgeon pin diam will often suggest where they might be, chronologically. ??
And overall piston height....

Have fun !
Title: Re: Pistons
Post by: Dads bike on 11 Jan 2022 at 13:34
Afternoon Roy
I may be able to offer some help regarding the numbers that you listed
The Hepolite info that I am looking at is thier 1939 catalogue.
The highest piston ref number is in the 8000s therefore I guess the 9747 and 9749 may we'll be post war?

Ref 4870 is for the 1932 K32 350cc OHV machine. It is an aluminium piston (not heplex) of 60.8mm dia with three rings and has a flat head.

Ref 1600 Is for the 1926/9 350sv models B28, B29, EW and is the aluminium piston type (not heplex) of 60.8mm with two rings and a domed head. (NOTE 1602 is the cast iron type if you should have them)

Ref 5788 is a bit of an enigma! It is listed for the 1935 750cc OHV special?? Again this is an aluminium
(Not heplex) piston it is 76mm dia with one compression ring one scraper ring and one oil ring that is below the pin and a flat head. I don't know the machine that this is for.

I do have some other info for later machines but currently cannot find it.
Let me know if I can be of further help.

Steve


Title: Re: Pistons
Post by: Red on 11 Jan 2022 at 15:12
Thanks Steve that is very helpful.

We seem to have 2 x 4870 Std pistons and 2 x 1600 Std pistons. Anyway I have got a long way to go in sorting what we've got but all information I can get will make it a bit easier. Thanks again

Roy
Title: Re: Pistons
Post by: Tazmantic on 11 Jan 2022 at 16:16
Hi I've just bought a 1930 to 1958 list so this might give some info when it arrives
Title: Re: Pistons
Post by: Tazmantic on 11 Jan 2022 at 16:39
Afternoon Roy
I may be able to offer some help regarding the numbers that you listed
The Hepolite info that I am looking at is thier 1939 catalogue.
The highest piston ref number is in the 8000s therefore I guess the 9747 and 9749 may we'll be post war?

Ref 4870 is for the 1932 K32 350cc OHV machine. It is an aluminium piston (not heplex) of 60.8mm dia with three rings and has a flat head.

Ref 1600 Is for the 1926/9 350sv models B28, B29, EW and is the aluminium piston type (not heplex) of 60.8mm with two rings and a domed head. (NOTE 1602 is the cast iron type if you should have them)



Ref 5788 is a bit of an enigma! It is listed for the 1935 750cc OHV special?? Again this is an aluminium
(Not heplex) piston it is 76mm dia with one ring and a flat head. I don't know the machine that this is for.

I do have some other info for later machines but currently cannot find it.
Let me know if I can be of further help.

Steve

Hi Steve,

I have a piston that I believe is a aero 250 there are 2 numbers one I can read 2102 the other I cant as the inside of the skirt has been machined slightly but I think its 8875. Do these match anything in your book?

Cheers
Title: Re: Pistons
Post by: Dads bike on 11 Jan 2022 at 17:33
Evening

The only ref no for the 1934/36 250cc sv is 5322. a 51mm aluminium piston with three rings (two compression and one scraper) and the machine descriptions are for the Comet, Y, 5Y
See if I can cross ref your nos with anything else?

Steve
Title: Re: Pistons
Post by: Dads bike on 11 Jan 2022 at 20:06
Evening
Hopefully have attached Douglas info from 1939 Hepolite brochure
Steve
Title: Re: Pistons
Post by: Dads bike on 11 Jan 2022 at 20:07
Last two
Title: Re: Pistons
Post by: Dads bike on 14 Jan 2022 at 11:41
Morning Roy
A little more info, this time post war Hepolite piston ref numbers.
Hopefully helpful.
Steve
Title: Re: Pistons
Post by: Red on 14 Jan 2022 at 13:58
Hi Steve

Thanks for that. Every liitle bit of information helps

All the best

Roy
Title: Re: Pistons
Post by: cardan on 15 Jan 2022 at 05:09
Ref 5788 is a bit of an enigma! It is listed for the 1935 750cc OHV special?? Again this is an aluminium
(Not heplex) piston it is 76mm dia with one compression ring one scraper ring and one oil ring that is below the pin and a flat head. I don't know the machine that this is for.
Hi all,

Presumably the 76mm pistons "1935 750cc OHV special" go in machines like the Bury bros sidecar racer from the mid 1930s? 76 x 82 gives 744 cc - close but not equal to the 746 cc usually quoted for these engines.

https://www.douglasmotorcycles.net/index.php?topic=5444.0

There's also high compression racing version (and an aero version) in the catalogue Steve posted.

Leon