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Author Topic: four smoking guns  (Read 2410 times)

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viking

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four smoking guns
« on: May 22, 2005, 05:48:59 AM »
hi, i have a 73 cb500 f, it starts easy, idles and runs good, but after som hard riding it starts to smoke badly,(grey/blueish), but it  stil runs good, anyone have an idea of what to look for? i have only had the bike for 3weeks.
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Offline Gordon

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Re: four smoking guns
« Reply #1 on: May 22, 2005, 06:10:04 AM »
Bluish smoke is an indication of burning oil.  Could be any number of things like worn/stuck rings, or bad valve seals.  Is it definitely a blue smoke?  If not it may just be running rich.  Check the plugs.  They're probably black either way, but are the oily black or sooty black?
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viking

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Re: four smoking guns
« Reply #2 on: May 22, 2005, 06:17:10 AM »
the plugs are more like sooty black,and the smoking started on one pipe , but is now on all four,it smells like a two stroke
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Offline bryanj

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Re: four smoking guns
« Reply #3 on: May 22, 2005, 08:04:24 AM »
Almost certainly valve stem seals with a secondary of stuck rings. At least the top end comes off in the frame on these
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

viking

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Re: four smoking guns
« Reply #4 on: May 22, 2005, 09:53:55 AM »
thanks guys, guess its up to me and the spanners now :) as a former BSA ovner im used to that ;D
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Offline TwoTired

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Re: four smoking guns
« Reply #5 on: May 22, 2005, 10:45:48 AM »
Blue exhaust smoke is indeed an indication of oil burning. 
Are you using any fuel additive that could contribute to this?
Often oil burners will show the symptoms on the spark plugs.  This site:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
 shows a plug with oil deposits.  But, I've seen examples where the deposits were much more bilowy.
Oil can get into the combustion chambers via the rings or past the valve guide.  You can get an idea of which to focus on by doing a compression check on the hot engine.   Take out all the plugs and record the highest compression reading you can get on each cylinder while operating the kick starter.  Now, put a half teaspoon of oil into each chamber and repeat the procedure for a second set of numbers.  Now analyze the data.  All the numbers from each test suite should be within 10% of each other across the cylinders.  If the oil has helped seal the rings, then the second set of numbers will be higher than the first set.  If the added oil didn't make a compression difference, then the blue smoke can be oil getting in past the valve guides.  In worn out engines, both problems can occur.

Heads up putting the cam cover back on: back way out all the tappet adjusters so they won't catch on the valve stem and bend valves during reassembly.

Cheers,

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Lloyd... (SOHC4 #11 Original Mail List)
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