Dear Nortonis,
Here's a strange tale. I have a 74 MK2. I inherited it in a barter for design work with a great MC gear shop here in Brooklyn called Union Garage. Love the bike though as an old airhead wrencher I had many lessons to learn. It was a heavily modified bike with a Harley style drum oil tank and many unsavory details. I cleaned up many of them and fitted an older style square oil tank. When I started the bike it pushed oil out of every seam and fitting. So I installed one of Jim Comstock's sump mounted breathers, filled the various holes between the crank and timing case put some 40 weight oil in and as soon as the weather cleared (this week) I went for a ride.
All was well until about a half hour in, traveling around town, when I see white smoke coming from both exhaust pipes. I rode about four blocks to my shop and had a look. I noticed that the thick neoprene rocker cover gaskets sold as a remedy for poorly fitted covers had separated. I had a closer look and discovered that they had shredded inside the engine and some neoprene was hanging around the valves.
So I did a compression test - 130 in both cylinders and I did a leak down test 9% both cylinders. Then I took the oil return line off of the tank and kicked it over. No oil flow.
So now I suspect that the oil pump or a passage is clogged by the damn neoprene. I'll pull the timing cover and have a look. Do you think my logic is sound? Is there anything else that comes to mind that I might have missed.
Thanks in advance for your help.
The oil return won't show…
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James, First thing to do i…
James,
First thing to do is as already mentioned - remove sump filter; this will allow you to see if it's blocked and you will also find out how much oil is down there. Don't know about your breather conversion; does it return oil to the tank as well as pump? Also you should have car style disposable filter does it look like it's time for a change ?
Finally for our avid readers - How much oil was left in the tank?
regards Martin
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Robert and Martin, Thank'…
Robert and Martin,
Thank's so much for the advice.
Here is a photo of the Comstock sump breather and it's filter. It screws into the sump plug and connects to the top of the oil tank.
The recommended installation is to plug all passages from the crank case to the timing chamber and drill a new 1/4" passage at the bottom of the oil pump. That is what I did. It was done quite carefully.
The bike does have a disposable car style filter mounted behind the transmission that was replaced with the breather installation.
With this problem there remained a good amount of oil in the tank. It was halfway between the marks on the stick. The oil was a bit frothy on top. With the engine was running very hot, the white smoke and given reasonable compression and leak down is it safe to narrow the problem to insufficient oiling at the head?
Can I assume that if oil is being returned to the tank the pump is doing it's job? Can you recommend a convenient way to check for oil flow to the head and the strength of the oil pump? I'm thinking of some clear tubing for the rocker feeds and perhaps a gauge.
I'll drain the oil, check for bits, and try to clear the passages. Seems like a good idea to open up the timing chamber and have a look too.
One more question - my airheads typically show about 155 pounds of compression with the gauge I use. Would you consider 130 to be a bit low for the Commando?
Sorry for all of the questions - thanks again! Jim
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The smoke is more likely t…
The smoke is more likely to be caused by too much oil in the head,particularly as you have gasket stuff up there floating around which could have blocked drainage . If the oil is frothy in the tank thats because it normally is .If you look into the tank you should see an intermittent return flow as it normally clears the oil faster than the supply and so brings up air. !30 could be fine, depends how it was done.I supose its possible that the oil scavenge is blocked and your engine is blowing some but not all the extra sump oil back to the tank thro the comstock.And the excess sump oil is making the smoking happen. love a good mystery!!.
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The oil return won't show much of anything at kickover speed, The sump filter ( if you have one?) would catch anything before the pump. You could have blocked the drain hole in the head , With a bit of care you could poke some wire down there. drain the sump and clean the filter, use an old vac to suck out the bits from the head , Duct tape a small bore pipe to it. If you are taking the pump off you could blow compressed air back through the pick up to clear blockages.