How to tell crank seals need replacing?

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How to tell crank seals need replacing?

Post by SeanW » Thu Apr 25, 2019 12:54 pm

My project KR-1S came to me in boxes and with a damaged piston (broken ring) and barrel and one side so I have no knowledge of how it was running (clean/smoky etc) before it broke. It has 19k miles on the clock which from mot history look like they're genuine

I'm stripping it down (currently stopped as waiting for flywheel puller to arrive) but when I do get it all apart I'm wondering about a few things.

Rather than replace/refurb everything just in case, I'm initially thinking of just fixing the obvious stuff (ie wrecked piston/barrel) and seeing if it runs OK.

So my question is, are there any obvious signs that would point to the crank seals being past it/damaged, or the crank bearings for that matter (beyond just spinning them or listening to them). As it's a specialist job to pull the crank apart and replace seals and bearings it would probably be better to get them done them now rather than later if it's clear they do need replacing. But if they are in OK order, then I'm happy to leave them alone for this summer at least. I'm just not sure how I'll know one way or the other...

I guess it's possible that fragments of broken ring could have made their way into the bearings so maybe the correct approach would just be go for a full crank overhaul?

What would people's experience suggest here?

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Re: How to tell crank seals need replacing?

Post by Garry » Fri Apr 26, 2019 7:16 pm

Well personally i always run an engine first to see if any major work is required - should soon become

However since you only have 1 cylinder you have a bit of a problem

Bottom ends seem pretty good/long lasting on these.

I had a seizure once - used a piece of petrol pipe taped to a vacuum cleaner nozzle to clean all around the
crank in case any debris in there. Guess you could also rinse out as well if your engine is out.
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Re: How to tell crank seals need replacing?

Post by maccas » Sat Apr 27, 2019 7:49 am

I'd be rebuilding the crank if I were you. 350-400 quid and it'll be like new. The crank has a habit of the centre bearings spinning on the shaft.

Send it to bdk, grampian or PJME. All of them will be able to sort you out.


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Re: How to tell crank seals need replacing?

Post by podman » Sun Apr 28, 2019 8:25 pm

Age/storage conditions hit seals harder than mileage...

You can only imagine how gutting it is to rebuild an already stripped motor and then have to remove it from the chassis and split it right down again because a few quid seal is goosed..

2 strokes don't do short cuts (especially old 2 strokes..) and will hit you in the wallet hard...if the left hand seal is goosed it could suck in air and seize that newly repaired barrel and piston...

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