Author Topic: Douglas piston rings (Read 19130 times)

Mike · « **on:** 27 Oct 2004 at 20:24 »

Hello. My name is Mike Porter. I run Porter's Motorsports and have a customer bike which is a 1948 T-35 that minimally needs piston rings but I would like to find pistons as well in oversize so as to bore the cylinders.
I gather there is a Japanese piston that will fit but have no idea what make or model. Any help you can provide is greatly appreciated. thanks, Mike

Doug · « **Reply #1 on:** 29 Oct 2004 at 03:00 »

Mike,

You will need to determine if it is a 1946-48 T35 or a 1948 Mark 3, which started shipping in June that year. The T35 has domed pistons, and the Mark 3 through 5 series has flat top pistons. Barrels and heads are different, though the whole cylinder assembly will interchange; the bore is the same at 60.8mm. T35 hemispherical heads requiring the domed pistons are readily identifiable by the name 'Douglas' cast into the rocket covers.

Mark series pistons are made by Peter Hepworth in the UK, but many folks complain they are prone to passing a lot of oil and smoking. My personal experience confirms this. Do not know of a source of T35 pistons; so you might be better off with just a ring job in any event. Using Mark series pistons in a T35 would result in an abysmally low compression ratio.

I have heard tell of Japanese piston conversions, can not recall what was used, but seems to me it involved boring the cylinder out beyond its maximum limit.

-Doug

Mike · « **Reply #2 on:** 29 Oct 2004 at 03:32 »

thanks for the info.this is not a 1948 then according to the description.it has domed pistons and is on the original bore of 60.8mm.do you know where i can obtain ringsets? oversize would be ok as i can file them to achieve correct end gap.thanks. mike

KiwiJohn · « **Reply #3 on:** 29 Oct 2004 at 07:39 »

Don't give up on the Japanese pistons, I am sure excess boring is not necessary but I cant find the information just now.

However take a look at http://www.douglasmotorcycles.co.uk/ who have all the information and spares you might need. I highly recommend joining or telling the owner to join.

Doug · « **Reply #4 on:** 29 Oct 2004 at 12:01 »

Mike and KiwiJown,

I agree, the owner ought to joint the London Douglas Motor Cycle Club. They sell the Peter Hepworth pistons, and might also have just the ring sets in their Post-War Spares department.

But, currently they can not sell spares to North America due to liability insurance issues. They are trying to find a new inusurance policy that includes this coverage, yet is affordable.

You might do better to try to track down the Hepworth firm and order directly.

-Doug

Mike · « **Reply #5 on:** 29 Oct 2004 at 13:52 »

thanks gents.yes i have emailed the club to no avail.i simply get a reply to do as you say but have found no parts available.why would there be any liability issues? makes no sense to me.i will wait for more info since i am a neophyte about these bikes.my knowledge is in asian bikes so any help forthcoming is appreciated.

Doug · « **Reply #6 on:** 29 Oct 2004 at 15:02 »

Mike,

The liability issue is this:

The LDMCC carries insurance for club events and for selling spares which they have manufactured for sale to members. In the last five years, their insurance companies have either dropped the club's policy, or raised the premium cost astronomically if the club continues to supply spares to North America. The insurance companies view the North American market as high risk for product liability lawsuits; wonder how that happened. Even though the club might have disclaimers and such as to limited liability in the sales of spares, the insurance companies do not feel this is adequate protection and adjust their rates accordingly. Without insurance protection, the club feels that members of the committee could be held personally liable. In the worst possible case literally lose their homes for volunteering to serve as a club officer.

The LDMCC is not the only small one make club in this situation, several other clubs I know in the UK have had to enact similar policies due to the inability to get insurance at a reasonable rate. It is a sad state we have come to.

-Doug

KiwiJohn · « **Reply #7 on:** 30 Oct 2004 at 08:51 »

Mike,

I have found reference to using Honda 250N pistons but it is unclear to me what is required in the way of boring etc and the Honda pistons are not so high crowned as the T35 pistons leading to low compression. Not as simple as I thought.

However I may be able to find some good information for you, if sucessful it will show up here!

Mike · « **Reply #8 on:** 30 Oct 2004 at 21:36 »

thanks again for the replies.too bad the greedy ass attornies of the world cant find legitimate ways to make a living,[just my opinion].anyway,i do need some rings so if anyone can find some please advise.thanks again.

Dave · « **Reply #9 on:** 30 Oct 2004 at 22:29 »

Did a quick search... these people might be worth faxing or emailing.

Peter Hepworth Components, York, UK
Cylinder liner, engine chassi & brake components manufacturers
Crayke
York
YO61 4TB
United Kingdom
Tel: (01347) 821340
Fax: (01347) 822942
http://www.peterhepworth.com

Board Bros, London, UK
Piston & piston ring wholesalers
103-105 St. John's Hill
London
SW11 1SY
United Kingdom
Tel: (020) 7228 6846
Fax: (020) 7228 8136

Motive Components Ltd
Motor vehicle parts
13 James Way
Bletchley
Milton Keynes
MK1 1SU
United Kingdom
Tel: (01908) 368995
Fax: (01908) 373722
http://www.motivecomponents.co.uk

Bradford Piston Rings
One of the few manufacturers of piston rings and sealing rings in the UK
Unit 22
Missouri Ave
Salford
M50 2NP
United Kingdom
Tel: 0161-736 5211
Fax: 0161-736 4785
http://www.bradfordpistonrings.co.uk

Cambridge Motorsport Ltd
Caxton Rd
Great Gransden
Sandy
Beds
SG19 3AH
United Kingdom
Tel: (01767) 677969
Fax: (01767) 677026
http://www.cambridgemotorsport.com

They offer a custom piston service
http://shop.cambridgemotorsport.com/department_template/departments.cfm?id=16&template=je_pistons.cfm&CFID=700297&CFTOKEN=96160932

Mike · « **Reply #10 on:** 01 Nov 2004 at 15:00 »

thnak you.i have emailed these companies and wait to see what happens.

Doug · « **Reply #11 on:** 03 Nov 2004 at 03:08 »

Mike,

I have made a slight edit to my post above. Seems the T35 or Mark 1 models were made into 1948. Early in 1948 they were working on the cylinder head redesign; prototypes were available in April for testing. By early June the road test appeared in the Motor Cycling, and the factory was shipping out the Mark 3.

Mark 3 models were numbered from 4001 on, though as I said someone could have interchanged early cylinders and heads onto a later crankcase. So you can not go just by the numbers. Engine/frame prefix is not to be counted on either. All T35 or Mark 1 and the early Mark 3 models shared the same prefix of T35/S/****.

-Doug

bmwmyplace · « **Reply #12 on:** 05 Nov 2004 at 10:29 »

Hey Mike try this link they make pistons and rings for some douglas bikes and will also make to sample Regards Peter
http://www.jp.com.au/JPPistons.html

Mike · « **Reply #13 on:** 09 Nov 2004 at 13:42 »

thanks again.i have emailed these companies.no success yet but i appreciate the help

tommy · « **Reply #14 on:** 09 Nov 2004 at 21:12 »

Hi guys,
Just to let you know the best pistons to use are Honda 750 K4 ( I think from memory )
You have to bore to maximum, but the chances of you clocking enough miles over the next 20 years to wear out are slim!

You do have to alter the small end bush for the pin, but it is a small job.

The compression is spot on and the alloy used for the Honda piston is first rate (low expansion).

I have them fitted in my MK4 and it pulls like a train, with no smoke from first starting onwards.

I have also fitted them to an 80+ I am building, but it is not finished yet.

The pistons are available from Dave Silver Spares and from memory are around £100.00 for a pair including ring sets and pins.

I am sorry, but I do not have all the info to hand right now, but I will find the part numbers, telephone numbers for Dave Silver and notes on bore size and clearances given ect and post them on the site for you.

This is an easy fit, no messing, low cost cure to the problem and it definately works.

Hope this is of some help.

Tom Rees