End pads for Gudgeon pins

[Keith]

I'm using a pair of cast iron pistons in my rebuilt CW motor. It has the fully floating gudgeon pins but not the ends pads.
I'll make these up out of some PB2 rod, but wonder how much end float I should allow?

Thanks, Keith....

[cardan]

Hi Keith,

I never measure it because it doesn't matter very much - just allow plenty of over-all clearance. Say a mm or two. Radius the ends to something a bit smaller than the bore (so there are no sharp corners if some contact occurs), and drill a small hole to make sure there is no pressure build-up when things get hot.

Well done for using cast iron pistons. I think it's a great way to maintain the original feel of an old bike. I do it when I can.

Cheers

Leon

[Keith]

Good point about the pressure build up Leon - I never realised that the pads were fitted that tightly into the pin 
My pins are solid so I'll have to drill into the ends to create the hole for the pads to fit in. The pins seem to be hardened on the outside but not the ends, so I should be okay.

[cardan]

Solid pins... what are they made from? I have used "linear shafting" on occasion, and that is hard on the outside but easily drilled up the centre. You don't have drill all the way through.

I have a knowledgeable friend who swears that teflon is OK for the endcaps. I used it once, but the engine wasn't mine and I don't think the bike has been used.

Cheers

Leon

[EW-Ron]

That sounds a wee bit like the story of Villiers (are we allowed to mention them here ?) who were experimenting
with some form of plastic big end bearing (nylon ?).

The engine was on test, but came to a bit of a strangled halt.
The technician went to remove the spark plug, but "was startled to see the spark plug snap back almost into position."
Apparently the nylon had migrated a fair way throughout the engine....
Make sure your chosen plastic is sufficiently heatproof. ?

Teflon is probably a good choice.

[Keith]

I'm pretty sure that my pins have been made from linear shafting. I did a test drill on the lathe with a center drill pilot hole followed by a 3/16 HSS bit and it all went smoothly. I'm just wondering how deep I should go. The old pads I have seen did not have more than 5mm or so of spigot to go into the pin. Are they supposed to be a tight fit in the pin?

Yep, plastic can be a real pain to remove once its melted onto a surface. There are some modern high temp ones around (think of the 'oven ready' meal containers etc.), and certainly (some) teflon is high-temp rated. But I think I'll stick with the old PB2 bronze as it seems to have worked fine for over century 

[cardan]

No they don't have to be a tight fit in the pin. Just a spigot to stop them turning sideways!!

Cheers

Leon

[Bob M]

Of course you can mention Villiers here Ron. Even Douglas made a Villiers powered machine. The first year of the Douglas Bantam was Villiers powered before they made their own two stroke engine. This is the top Douglas on my shopping list, followed by the EW of course.

Anyway, gudgeon pin end pads. Villiers used a 1/2" solid gudgeon pin with bronze endpads on all their engines for donkeys years. I've never found a pre 1940 engine without them. I don't know when they finally dropped them. All with a little pressure relief hole as Leon says. From memory it is 1/16" but don't hold me to it.

Teflon was used for end pads as well but the only examples I know of were in American competition pistons where life expectancy and usage would be very different from what you are aiming at. Bronze works quite well and is easy to machine, why change?

Cheers, 

[Keith]

Job done.
Thanks for the guidance and help   

Cheers, Keith...

[tck]

I have found engines with aluminum end plugs I cant see a problem with that after all pistons are often alloy and if you were substituting end plugs for unavailable gudgeon pins or circlips alloy would not affect balance.

[graeme]

I have used teflon pads in a couple of race engines, and they work well