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🏠Home🏠RC Main Discussion › Wrist pin retainer
04-30-2021 04:21 PM  13 days ago
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Evolusia

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UK

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Wrist pin retainer
Hi, can anyone give a heads up on the type of material (plastic) used as a plug in some engines to retained the wristpin. Tia.
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04-30-2021 07:36 PM  13 days ago
dgoss999

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Probably a plug of PTFE..

DG
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05-01-2021 01:15 PM  12 days ago
wjvail

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Meridian, Mississippi

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I don't know exactly what material manufactures actually use. It's probably a note on some design drawing. PTFE would be a good guess.

Just about anything you can get easily get your hands on softer than steel would be acceptable. PTFE melts at about 620F and it not mechanically very strong. That suggests the little pad doesn't see much heat or load and many other materials would work. For instance, I've seen brass or bronze also used. Anything to keep the pin from brushing the liner.

Over the years I've seen modelers run engines with no pad at all. Typically they lost the pad while the engine was apart and didn't know one was to be installed. While I don't recommend it, the engines only showed a light scuff mark where the pin touched.

Anyway... I'll be interested to hear what others say.

Cheers,
"Well, nothing bad can happen now."
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05-04-2021 08:30 AM  9 days ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
/

I see your point.

I liked the regular pin retainer...

But, os15hz pin retainer was a pain in the neck.
We had serious problems when we tried to repair a OS15HZ.

Not easy to handle.
One of this monster got loose and damaged the liner.

/
Saludos cordiales,
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05-04-2021 03:35 PM  9 days ago
wjvail

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The small pads work well but, as you know, they can only be used where the wristpin (gudgeon pin) doesn't coincide with a transfer or exhaust port. For this reason these small pads are common in our 4-stroke engines but less so in 2-strokes.

It is common in our engines to have the exhaust out the starboard side of the engine which puts the two transfer ports fore and aft and directly in line with the wrist pin. The situation is similar for rear exhaust 2-strokes.

There have been instances in the past where the liner has been rotated in the case to allow a 2-stroke to avoid using common e-keeper. The OS "LA" line of engines comes to mind. While they had the typical side exhaust, the liner was rotated and the engines were able to use the small pads.

A 4-stroke doesn't have any "holes" in the liner so this is never a problem.

But you knew all that...

"Well, nothing bad can happen now."
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05-04-2021 04:10 PM  9 days ago
Evolusia

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UK

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Yes I did, unfortunately what I didn't know was that Thunder Tiger swapped from circlip to retainer plug for securing the wrist pin at some time during the production of the old pro 36h and hence there is no circlip groove in the later production pistons. Although they are still available it's not economical to get a new wrist pin assembly to my door what with shipping and all the thievery from Customs and Excise so before I turn one out of brass I was wondering what the plugs are made from.
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05-04-2021 05:09 PM  9 days ago
wjvail

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Meridian, Mississippi

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I have made little wristpin pads in the past. While I have a small lathe, they wouldn't be difficult to make using a hand drill. I made mine out of Teflon but again, just about anything softer than steel should work."Well, nothing bad can happen now."
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