Monday, 30 November 2015

RG 500 stripdown

So if you remember, the last outing on the RG ended with what I thought a small seize at the end of the straight at Ales.

Well I was kinda putting off, stripping it down (for fear of what I would find), but over this last week, finally got down to it. To be honest, I was considering just selling up, as the lack of reliability this year, has been a disaster.

Well it didn't dissappoint, I could see with just the head off that something had been bouncing around in there, with impacts on the head. After pulling the cylinder, I found a part of  a thrust washer sitting on the inside of the crankcase, about two thirds of it. The other third had wreaked havoc around the the piston, cylinder and crankcase.

The piston  has a slice taken out of it, and unfortunately the cylinder aswell, from the central transfer port down about 1 cm. Difficult to see on the photos but here they are anyway :-
The cylinder is basically toast... although will now need to investigate a new sleeve, which holds it's own complications as that would that cylinder back to the standard bore whilst the others are all 1.5mms bigger.... maybe need to re-sleeve all....
To add insult to injury, the piece of washer had also tried to escape through the rotary disk, so that needs changing as well!
I continued to strip the engine down, and although there are some impact marks on the conrod, I don't think there is any damage to the bearings... although I will need to get it checked professionally, as the last thing I want to do is have it go again. 
The cylinder head is going to have to be OK, after some filing down of the impacts.
I have decided that I will build it back up and not part it out, but I will not run it again until I get airboxes built, although none of these break downs are due to stuff getting in from outside.
I now think the reason that the thrust washers keep breaking, are that there is not enough clearance between the piston webbing and the thrust washers.
I measured the failed piston gap between piston webbing and it was machined to 21.9mms. The gap on a standard piston is 22.2mms, so missing 0.3mms of clearance. If you remember I had to open out the clearance on 3 of the pistons that ALCO did as they not machined straight - well this was the only piston I did NOT touch, and I think that was the reason for the failure.
The clearance of the other pistons (that I machined) is larger than the standard Suzuki clearance, I am pretty convinced that having a slightly bigger clearance is better, as long as (of course) the conrod can not move to touch the crank webbing.
Anyway sorry to be so wordy..... the bench is very busy....

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