Worn crank case seals

clive.rickman
Posts: 29
Joined: Fri Sep 23, 2022 2:57 pm
Contact:

Worn crank case seals

Post by clive.rickman »

I have completed some re-commissioning work on an Ariel Arrow which has been dormant for an unknown period of time. The carb has been checked and cleaned and the ignition system 'revived'.

I have fired up the engine and found that it'll only run consistently on full choke. When the choke is opened, the engine will die unless the throttle is wound fully open. (I have established that the problem is not due to low fuel level in the float chamber).

I am thinking the problem could be faulty crank case seals. Is there a way of assessing the condition of these without an engine strip? I can't find the crankcase plugs found on some 2-stroke engines, which I could use to attach a pressure gauge. If the seals do need replacing, I guess that'll require a crankshaft rebuild, in order to access the centre seal?

I'd be grateful for your help & comments.
will_curry
Holder of a Silver Anorak
Holder of a Silver Anorak
Posts: 959
Joined: Thu Oct 08, 2015 12:56 am
Contact:

Re: Worn crank case seals

Post by will_curry »

It does sound like seals to me - especially as it's been standing for a while.

If you search the forum I think there is at least one thread on pressure
testing two-stroke seals but I don't think it's a simple process as there
aren't crankcase drainplugs as standard.

When you replace the seals do get modern ones, not old ones, they go brittle
with time.

The crank has to come out to do the centre seal and I'd do the main bearings
while I'm in there. There is an allen bolt holding the two halves on the crank
together. Separating the two halves is all the crank dismantling necessary.
It shouldn't be a major effort as the allen bolt also acts as an extractor once
unscrewed a few turns.

Do use an extractor to get the crankcase doors out - they'll break if you try
anything else.
clive.rickman
Posts: 29
Joined: Fri Sep 23, 2022 2:57 pm
Contact:

Re: Worn crank case seals

Post by clive.rickman »

Thanks for this info, Will. Good news regarding the crank dismantling procedure! You mention an extractor for crankcase doors - any idea where I can find one of these?
JohnnyBeckett
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 2381
Joined: Sat Jul 07, 2018 5:39 pm
Contact:

Re: Worn crank case seals

Post by JohnnyBeckett »

hi, you can keep looking on ebay for a puller they do come up from time to time just keep looking under Ariel parts
bh.sprint
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 425
Joined: Wed Oct 31, 2012 7:21 pm
Location: South Yorkshire
Contact:

Re: Worn crank case seals

Post by bh.sprint »

Hi, Draganfly are the main suppliers of the extractors but as mentioned they do come up on e-bay or at Ariel Rallies etc. I supply a few occasionally but have only just got back into the workshop after having a new roof/wall , so am not taking any new orders for the time being. Brian H. arielbikes.co.uk
will_curry
Holder of a Silver Anorak
Holder of a Silver Anorak
Posts: 959
Joined: Thu Oct 08, 2015 12:56 am
Contact:

Re: Worn crank case seals

Post by will_curry »

Any decent beam extractor should do the job. The important bit is to use
the two holes specially provided in the doors which if memory serves me
well are tapped 1/4" UNC but do please check first . . .
bh.sprint
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 425
Joined: Wed Oct 31, 2012 7:21 pm
Location: South Yorkshire
Contact:

Re: Worn crank case seals

Post by bh.sprint »

Yes, the tapped holes in the cranckcase doors are 1/4 unc and the holes for the extractor in the flywheel are 1/4 unf. The extractor also includes a seal protector for getting the case back on but protecting the oil seal. Brian H.
Attachments
DSC00196.JPG
clive.rickman
Posts: 29
Joined: Fri Sep 23, 2022 2:57 pm
Contact:

Re: Worn crank case seals

Post by clive.rickman »

Thanks, Chaps! Useful to have a pic. I might make one if none available.
Ivor Collins
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 129
Joined: Sun Mar 30, 2014 11:04 am
Location: Leighton Buzzard ish
Contact:

Re: Worn crank case seals

Post by Ivor Collins »

How easily does it start? If it is the crank seals I would expect that to be a problem.

If you plug the the barrel exhaust ports, remove the carb and plug the inlet, you can pressurise the case and check for leaks but it will only check the outer seals. There is no way of testing the centre seal.
clive.rickman
Posts: 29
Joined: Fri Sep 23, 2022 2:57 pm
Contact:

Re: Worn crank case seals

Post by clive.rickman »

Thanks, Ivor. I have begun the engine strip now...
Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest