Polybushes

[Reckless Rat]

I'm sure most of you (unless you have an engine that is completely oil tight) have had to replace the engine mounting rubbers on the later crankcases. I have lost count of the number of times I have replaced mine, mainly due to the generosity of my engine sharing its contents with the wider world. I have given up trying to make it oil tight and live with it as it is, accepting its foibles as part of life's great tapestry.

However I am getting fed up as it's happened again - the rubber mountings "blow" and split due to the oil contamination, rendering them useless:



Being generally tighter than the windows on a submarine I have thought about alternatives and have made myself some replacements, using polyethylene bar at 90 shore. It is machineable on the Myford providing you use a high speed and a lot of positive rake on the cutting tool, which must be as sharp as possible. It's not the easiest of material to secure due to its pliability but you can get a good enough grip if you use a rotating centre.

Anyway, it's peeing it down here today so I've been busy. I obtained a short length of poly bar from Direct Plastics in Sheffield, but I'm sure there are other stockists near you. Here's the result of my labours thus far:



I'm using a spare crankcase just for fitting purposes. The poly bar as you can see is red but the material can be painted if necessary. I think I'll leave mine as they are.





The job's not yet complete as I haven't yet turned the small inserts for the mountings - due to the flexible nature of the poly I'm going to have to bore it first and then mount the material on a mandrel so I can turn down the outside diameter. That'll be tomorrow's task if it's still raining...

My thanks to Ruairidh for the dimensions.