Leaking Crankcase

[grahamcamm]

Took my silver century out today and noticed clean fuel leaking out of the crancase seal and sitting on the flat plate that the tiller bolts to. I wiped it away but it was back in seconds so it is continuously being forced through whilst the engine is running. Is it just the crancase seal or is it the piston rings? How much do I need to take apart? Thanks in advance

[phil]

Your options are to live with it, or to fix it. If it is not affecting motor running[runs well when cold, but not when warmed] you might leave it and wipe it down as needed. To fix it, take engine apart, lap the mating faces of the crankcase until they match seamlessly and reassemble. Usually caused by some undue strain or fall on tiller handle.

[grahamcamm]

What's at fault though? Is it normal for clean unburnt fuel to enter the crankcase? Do I put new rings in or just try to seal the crankcase or both? Thanks
ps the engine is a little awkward to start from cold (10 - 15 pulls) and needs to run on choke till its warm but runs well once warm. However, it doesn't seem to rev as high as other seagulls I have had

[phil]

Yes it is normal to have unburnt fuel in the crankcase. The fuel is drawn from the carb through the intake transfer port into the crankcase on the upstroke of the piston, the piston downstroke forces the air fuel mix through an internal channel to a port in the cylinder which is open on the last of the downstroke, it is then compressed by the piston and burned rapidly [exploded] when the piston reaches top dead center [TDC] Think of the crankcase as a holding area during part of the stroke.

It is not too likely that it needs rings unless the compression is unduly low [say 35 lbs.] use more than one compression tester gauge to eliminate possible error, unless you have one known to be accurate.

Reclean points and plug check for accurate gap, and clean entire fuel system several times if necessary to eliminate hard starting.

[grahamcamm]

Thanks Phil.
So if the compression is more than 35lbs I'll leave well alone. Do you think I should re-seal the crankcase with gasket sealant or leave this well alone as well?

Usually caused by some undue strain or fall on tiller handle.

I bought her off fleabay and this would tie in with why the throttle lever was snapped, probably had a bit of throwing around by the courior

[billyboy]

lap the mating faces of the crankcase

hi phil........ could you please explain a little about how one should do this? would appreciate it....Bill

[phil]

Composed an in depth reply taking about 20 mins after logging in, lost it all when it would not let me post without relogging in. Don't have time for that kind of crap!!

[phil]

OK Graham, ready to give it another try. Take motor apart, flywheel and mag off. Cylinder off. Leave piston attached to crankshaft if you want. Now find a true flat level surface, undo crankcase into 2 halves. Remove any locating dowels that may protrude. Now you should have 2 crankcase halves. You will need at least 1 sheet 220 grit wet/dry sandpaper and a thin lub oil. Kerosene[paraffin] works good. Paper grit side up on flat true surface, crankcase piece lightly held in fingers mating surface on lubricant covered sandpaper [ silicon carbide or aluminum oxide like the auto body paint shops use] Make figure 8s with mating surface of crankcase lightly held until newly surfaced area covers entire mating surface of crankcase half. Repeat with other one . Reassemble. I use the flat cast iron surface of my large tablesaw. As added insurance some use a sealant between halves on reassembly, most beginners use WAY TOO MUCH, no squeeze out allowed inside crankcase, check after test [without crankshaft] assembly and redo if any squeezed out.

[phil]

Plate glass 1/4" [6mm] or more thick, a new nicely polished gravestone, etc etc will also make acceptable surfaces to lap the mating faces of the crankcase on as well. If you haven't completely disassembled a motor before this is about the simplest one you could start on. Clear a good sized area and plan on 4-6 hrs of uninterrupted time, before the motor is running again. Fresh water motor!
As you disassemble lay pieces down in a systematic way that will enable you to reassemble logically and or take notes or photos.
After you have done a few you should be down to a couple hours start to motor running again.

[billyboy]

thanks for that phil. as a slow typist myself i hear you and appreciate the time. by the time i get some of my posts up somebody else has usually jumped in in the meanwhile either saying or asking the same thing!

[grahamcamm]

Thanks for the reply Phil

[Hugz]

Didn't I read somewhere that the factory used a hammer and punch and squashed the joint together if found leaking on final test? Sounds dodgy to me.

[charlesp]

You probably did read that here. Bashing back into shape requires lots of practice and it helps if you have a huge stock of spare crankcases if you get it wrong!

[Ian Malcolm]

I've had good results on a Forty Plus with a paper gasket cut to fit between the crankcase halves. It was proper gasket paper, pretty thin, doped with thinned Hylomar on all surfaces (or you could use the spray on stuff very lightly) and allowed to dry to 'fingerprint' sticky. It avoided all problems with squeeze-out and the block face was trimmed flush with a razor blade after assembly.

[Collector Inspector]

YEP!


That would do it Mate!

B