aero 250 spark plug issue and oil leak

[Tazmantic]

Hi all couple of questions for some reason the spark plug on the rear cylinder just wont seal, the seat is flat but new plug or new copper washer and it still blows bubbles if i put washing up liquid round it... any ideas

also the crank cases seem to be leaking quite a lot of oil out the bottom when parked (i didn't build this part) i really don't want to strip this down is there any additive I could add to the oil to stop this 

[Dads bike]

Evening.
Some points to look at
Ref the spark plug, A couple of raps with PTFE tape round the plug thread will seal any thread damage, If that doesn’t work next paint the cylinder head sealing face with something like pot black and put the plug back in whilst still wet.
Leave to dry and try again. If it still leaks you need to check for a cracked head.

The lower part of the crank case. Check the drain plug fibre washer, if over tightened they tend to crack and leak.
Other than that you will need to identify exactly where the leak is coming from.
Primary drive chain, is that oil mist Lubricated from the valve chest? Maybe just finding its way out and on to the lower crankcase.
Additives, don’t, they will cause problems to the crankshaft seal, magneto seals and Dynamo seals.
Are you using at least a straight 40 oil?

Hope some of that may help
Steve

[Tazmantic]

Thanks for the reply, I've put a smear of blue hylomar round the washer on the spark plug and that seems ok fingers crossed just odd as cant see any damage etc.

As for the oil leak it deff looks like is coming from the crankcases so looks like an engine strip  though I have removed the engine to frame clamps and see what happens as I'm wondering if as they are just flat plates maybe as I tighten them up they might pull the cases apart a nadgers...

[eddie]

If the leak proves to be coming from the crankcase joint, don't be tempted to use a thicker gasket - that will make the problem worse! Carefully file back any high spots until you can't get a 1½ thou feeler into any part of the joint, then rebuild with a thin gasket (5 thou max). Thicker gaskets will squeeze up around the stud holes, thus forcing the joint apart between the studs.

  Regards,
                Eddie.

[Tazmantic]

Hi Eddie,

Thanks for the reply, so it’s looking like an engine strip down then 

Cheers Neil

[Tazmantic]

So I did a little test and have come to the conclusion for some reason the plates that are clamping the engine down are some how spreading the cases, they are not the correct clamps just flat plates I’ve attached 2 pics fires is 2 days no clamps second is clamps nipped up over night....




[Edit image aspect ratio. 17Sep20 -Doug, Site Moderator]

[Dads bike]

Have you tried the clamps off your other machine, if they produce the correct clamping effect, then you will need to get some new ones cast.
I had some made up a little while ago, they’d were sand cast so not the prettiest and cost something like £20 apiece, pic attached

[Hamwic]

The results of your test would suggest that the centre distance of the lower frame tubes does not match the centre distance of the grooves in the cases. Either the frame tubes are too far apart or the pitch of the grooves in the cases is too close together. I would imagine that  the engine lifts when you take the clamp off, so some kind of surgery is required to make the two match. If the tubes can be seen to be parallel, then perhaps a slight easing of the channels in the crankcases is called for. If the tubes are perhaps spread a little, they could be carefully squeezed in to correct the pitch. However, as the alloy cases expand more than the frame when hot, perhaps a little extra clearance on the outside edges of the crankcase might be beneficial when the engine cools down?

[Tazmantic]

Thanks for the reply's, Ive ended up cutting the plates in half and welding a piece of square on the back edge so it touches the bottom of the engine when it clamps to the frame and all 4 are now independent. 2 days later and only one small drip so the plates must of been spreading the engine.....

Time to produce some better looking ones