Wartime piston

[JERSEYMAN]

I've got to say I've never seen a floating gudgeon pin without ally ends and if I remember right, the short water jacket barrels had bridged ports to keep the motor from self destructing.

[Salvtecmarine]

My engine did not have end caps on the pin, what it does have is, rounded polished ends, and from what I have seen on my other engine is it is identical, there are no pads on that piston / pin, if there were indeed pads fitted, were these a later addition or just omitted in later builds as they were not required?

As I have said, the bore is perfect with no scoring at all, the pin is polished at the end, which to me would say it has contacted the bore, I have not had a close look , but I will when I get home, but could there be wear pads pressed into the ends of the pin?

[JERSEYMAN]

A photo would be great, all the gudgeon pins I have ever seen on Seagulls have been hollow and with the early ones, ally pads pushed in the ends.

That's not to say solid pins don't exist, with seagulls anything is possible, that's why a photo would be great.

[jerseydave69]

Hello Jon

Thanks for the reply, put my mind at rest.
I checked the piston and it is the original hepolite, the big end has the hollow end cap on it too, it has the short water jacket and the piston and cylinder are in quite perfect condition for an engine built in the 40's,
Engine number Sdp8969

I just want to get it to an original working state, it has taken a few years to get its scars and scrapes, only things missing are carb, flywheel cover plate and bayonet cap for the tank.

Thanks

What I find interesting is , I have SDP8988 ! Mine doesn't have the circlips either, but has the aluminium looking plugs at either end

[headdownarseup]

Perhaps these pics might help.

Although these originally came out of a model D, going by the SD's SDP's and countless other "older" 102's i've stripped/rebuilt, these would appear to be the standard/correct parts for something built before (approx.) 1952/3. After this date, (possibly quite a bit later) the crankshaft looks to have been re-designed into the solid big end type with re-designed hollow gudgeon pin with circlips.
If there's anything in your motor that doesn't look exactly like this, then it's probably been apart in the past.

I have a few motors that date from the early 50's that follow the same internal build spec. , but as we all know, who knows what might (or not) have been changed over the years.

Jon

[Salvtecmarine]

Hi Jon

That's identical to mine, phew.....

I was a wee bit worried for a bit.
Thanks

[Charles uk]

Perhaps it's time that I made a statement regarding gudgeon / wrist pin usage in the Marston / British Seagull product range.

From the first 1931 Marston Seagull until some time in the late 40's, all the range 78, 102 & the 340 cc twins had floating gudgeon pins, so that's a piston with no circlips or circlip grooves & a pin with end pads, the cylinder also had bridged transfer & exhaust ports to prevent the pin catching in the port.

These pistons should not be used in cylinders that they were not designed for, i.e. post 1950 ish, a defective SD piston can be replaced with a piston set (piston, gudgeon pin & circlips) from any of the later 102 cc models, though it will be found that the piston's transfer port deflector notch does not suit the port dimensions as well as the original.

These pins were hollow with pads inserted into each end.

After this changeover Seagull only used hollow pins with circlips & one blanked off end, this pin should only be fitted with blank end uppermost to avoid the hollow in the pin filling with lube oil & increasing the weight of the piston & possibly causing balance problems.

[Adrian Dale]

Thanks Charles, so the inference is that on my OA and also the AD and OJ, the ally end cap is missing, lost from previous rebuilds? cant recheck the OJ and SD as they are both in the UK but will pull down the OA again, couple of things to do on her any way..

Good photo of the pin with the ally insert posted by Jon above.

AJ

[Charles uk]

I've never seen any of these pins with a pad or pads missing, but then I've only had under 40 of them in bits.

So no circlips must have pads!

On the OA undo the exhaust retaining bolts & rotate exhaust after pushing down to save gasket, on many you'll be able to see enough of the pin to check.

[Horsley-Anarak]

[Charles uk]

I could kiss you H-A!

But Won't.

[JERSEYMAN]

Great Pic

[Adrian Dale]

Great pic I have down loaded to my collection for future reference.. thanks AJ