The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Slymo on 17.02. 2019 04:39
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58SR is going much better now. I lifted the needle jet one notch and all but eliminated the pinking. It is however still smoking out the rhs pipe and has developed a wet sumping habit. It occurs to me though that I might have a leak from the oil pump gasket. Does that cause a smokey right hand pipe in anyone’s experience?
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can't see why an oil pump leak would affect on cylinder more than the other.
when you say smoke, do you mean its running rich (sooty) or burning oil (oily wet plug etc)
my SR always runs richer on the right. i think its to do with a slight bias on the porting somehow, aiming more fuel towards the right. (someone with a better memory will be along in a minute). also i discovered my timing was different left to right (as i recall it by about 4-5 degrees) due to the cam ring being mis-ground (fixable), and correcting that helped a bit.
if its oily then that's a different story...
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No its definitely oil smoke not rich mixture.
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I had to retorque my head gasket to clear up a smoky right hand side.
Lee
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I replaced the scrapper ring on that side and replaced the head gasket but this made no difference.
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usual suspects: when apart did you check the bore clearance and valve guides?
hows the compression?
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Rule of thumb
Smokes on acceleration = rings
Smokes on deceleration = Valve guides
Which one you got ?
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Neither, both are mint however as I suspected the timing case was full of oil and it seems the oil pump was leaking from the gasket joint. The pump is an original mazac one and has begun to grow out of shape. Ive flat filed the face and made a new gasket and will see if it back syphons the oil as fast once I refit it.
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And don't forget the little round gasket under the forward fixing on the pump.
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Worth checking the scavenge side of the system for air leaks and obstructions, as these this will result in wet sumping. The timing bush will vent oil into the oil pump cavity, where the level rises to the keyhole, and the oil then overflows and passes to the sump. Some oil is normal around the pump but the timing case cannot fill with oil entirely. A badly worn timing bush will also vent a lot of oil against the crank web, and get thrown up the bore. Easy to check for lift in the bearing with the pump off.
Sorry, but I cannot understand what is meant by "back syphon" in this context, but I suspect you mean " returns oil to the tank."
Swarfy.
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The oil tank being so high maintains a positive pressure on the pump so I agree not really a siphon more just pouring in from above. Re the washer under the front of the pump. I’ve assumed this is simply a spacer which I will now need to modify as the face of the pump has been filed down somewhat. The question though is it simply a steel spacer or do I require a copper of aluminum washer to seal it?
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Hi Slymo,
The purpose of the fibre washer is to compensate for the thickness of the gasket on the front mounting
he crankcase should be flat and so should be the pump
A piece of the same material as the gasket is the best to use in my opinion, I make one piece gaskets with an extension to accommodate the front mounting
John
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That makes perfect sense but with my pump there is a distinct difference between the plane of the body and the end, probably 020" but I will compensate and make it fit. Thanks for the help all *smile*.
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Slymo, In theory the pump faces (body and drive spindle casting) should all be flat and in the same plane. The time honoured way was to assemble the pump, tightening the bolts bit by bit and twisting the body and spindle casing , checking all the time to try and stop it binding. Then rubbing the pump flat on a sheet of fine emery paper, supported on a piece of window glass. Then came the washing out of the emery dust and aluminium filings with petrol, turps or paraffin, whatever you had. These days blocking the holes would be a good idea....that was then.
An A65 pump gasket, with a strip cut out to shorten it, can be used to ensure all three pump mounting points are in the same plane in an attempt to stop the pump twisting as it is tightened against the crankcase.
Swarfy.
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That makes perfect sense but having made a reasonable fist of flat filing the mating face of the pump body when I pressed it down onto a sheet of glass I could still slip a .026" feeler gauge under the spindle mount. So Ive made a suitable sized washer on the lathe and then a 0.4mm gasket for for both sides.
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Vast progress in a number of areas other than smoke. Went for a 200 mile ride the other day and on going up the BIG hill on the ride I found that the bike was still pinkng like a bugger. Lifting the needle valve to notch four cured the flat ride pinking but clearly there was more to be done. I retarded the bike far more than usual and suddenly gained about ten horsepower and the pinking was gone. Got home and measured the full advance position with a stick down the plug hole and foumd it was the best part of 3/4" btdc. The sweet spot (surprise surprise) was about 3/8". Resetting the timing was interesting because about six times I reset the position to 3/8" only to discover that once tightened it had shifted to between 1/2 and 3/4". Finally got it set right and crikey what a difference! This old machine has some go. I've ordered a new set of rings and will pull the top end apart again when they arrive but until then I will contine to strop around making smoke.
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G'Day Slymo.
From the way you described adjusting the timing it sounds as if you have a manual magneto. For those of us with the ATD, you have to consider the backlash in the gear train and it was always a case of setting the piston height as usual, then moving the idler gear and cam wheel backwards against their usual direction of rotation. Then add the ATD, set and wedged at full advance again ensuring that it is turned with a clockwise bias against the cam wheel teeth. This means that all the teeth are set in light contact on their driven sides at rest and the variation in timing due to backlash is eliminated.
You know this, just posted for the benefit of those folks who perhaps have never considered this variable and wonder why the timing seems to have moved. Obviously this is not so critical with a manual maggy.
Smokin' on.
Swarfy.
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G'day Sly.
With the timing that far advanced she would have detonated like a Vietnamese rice paddy! Which may explain your smoke issue. Broken rings!
Yes fudging the timing so it's right when the nut is done up. Hands up who gets it right the first time?????
Cheers
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Pretty sure I haven’t broken any rings as I have a fairly gentle throttle hand. Also it’s smoked since day one. However I do think the rings are under par tension wise so a new set beckons. The nuisance is that the market seems crowded with “NOS” Hepolites which I don’t intend to purchase as I have severe doubts about the sudden influx to the market of sixty year old piston rings and if that is bollocks what else is. Gandini are proving elusive but Hastings Rings appear to be available. Does anyone have any experience with these?
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g'day slymo.
Hastings rings have a very good reputation, I wouldn't hesitate to use them.
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Finally found a source of Gandini rings so those are on order.