The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: sprint on 12.07. 2016 09:12
-
Trying to help a friend with a Road Rocket with heavy smoking on the RHS.
Soon after he bought the bike it started smoking on the RHS. We took the head an barrels off. Could not find anything amiss with the head/valve/guides. The RHS bore had clearly been bored slightly larger that the LHS but measured up OK. So the bores were honed and new rings fitted, which had to be filled to get the right gap.
Re-built the engine and low and behold the same problem still being experienced. Sometimes it will run fairly clear for a while but then it can start to smoke fairly heavily and if you are following the bike it is very oily smoke.
Anyway, decided that it may be wise to just run for a miles to see if it settles. Has done around 500 miles now with no significant change. Went with him for a run over the weekend and for about the first 40 miles it was fairly free of smoke but then it started to smoke very heavily on the RHS again and the last 30 mile home was in a trail heavily oil ladened smoke. When he got home he had lost about 3l of oil and whilst the inside of the RH silencer was coated in oil the rest of the bike was clean.
Drained the sump and about 1pt or so of oil out, which seemed fairly high but enough to cover the loss.
Have done a compression test and both sides give about 170 psi, so the indication are that the piston/rings and valves are sealing OK so what is causing the RHS smoking and massive oil loss?
Any thoughts and ideas as to what the cause might be or what we need to be looking for would be appreciated.
-
Drained the sump and about 1pt or so of oil out, which seemed fairly high but the enough to cover the loss.
Sounds like it is wet sumping check your oil return 1Pt oil in sump is a bit much *eek*
Peter
-
A cracked head " try a hot compression test.
A worn valve guide.
A blocked drain from the right side rockerbox.
Now for the rest of the story.
You were nice & detailed about the bores but ignored the pistons & heads.
Was the right heavily coked up or at the least significantly heavier than the left ?
If not then it is a safe bet that the oil is coming in from the exhaust side and blowing directly into the right silencer.
You would not normally get oily smoke from the exhaust.
You get instant London sunshine.
-
I just finished a RR engine that was doing almost same thing .
There can be various reasons but in my case it turned out to be the alloy head .
The crack was not obvious at first and when spotted did not seem that bad .
However when a machine shop checked it the crack extended from the pushrod tube holes across the head up the the combustion chamber and across a valve seat to the guide bore .
-
Thanks for the replies and advice.
The compression reading of 170 psi was with the engine hot, though only from running the engine and not after a long run. There is a manual valve in the supply oil line so not wet sumping from standing, so it could be poor oil pump scavenging or a problem with the oil pressure valve?
However, none of that explains how it lost around 2 to 3 l of oil in a 70 mile run which does not appear to have been dumped out of the breather but straight out the exhaust?
The RH piston crown had a soft black oily deposit when we took it apart last year but otherwise the pistons looked fine, but there may a fine crack? Head looked fine at the time with no apparent massive wear between the valves and guides. However, we did not make a very detailed inspection of the head, so a crack may be a possibility?
Looks like the head will have to come off again with a more detailed inspection of the guides and head for wear or cracks. Just wanted to get a better insight as to what the problem may be and where to focus attention.
-
Hi Sprint
Drained the sump and about 1pt or so of oil out,
so it could be poor oil pump scavenging or a problem with the oil pressure valve?
Way too much oil, it pumped burned the rest as it was driven, its not scavenging
Check for ,,
Dirt in the pickup pipe, the filter fitted wrongly
A magnetic sump plug with the magnet near the pickup *doh*
a loose breather sleeve (cork too thin)
loose oil pump mounting screws, or loose screws in the pump body
or a bad oil pump gasket
John
-
Or, flow and return hoses wrong way round.
-
Or, flow and return hoses wrong way round.
It would have seized in short order *eek*
John
-
I don't understand why it would cause a seizure. Its not a common mistake, but it does happen and it can cause exactly the symptoms described. If, as I know this has been done on AMC twins which have a 1/2" bore hosing hasn't caused a seizure just excess oil feed and insufficient scavenge. Causing too higher oil level in the sump etc.
-
Because the return line hole is above the oil level so it sucks ( or does not suck to be more accurate ) air down into the engine.
No problem for the return running backwards except the depositing of particualtes on the feed side of the oil tank strainer.
-
Fair enough! makes sense.
-
Sprint, Let us know what you find I'm intrigued, or should I say we are *conf2*
Peter
-
Well, we have replaced the pump and oil pressure valve with known good items. In the next few days will take it out for a run to see what happens, hopefully at least the oil loss should be sorted as it previously used to smoke but did not suffer oil loss?
If it still smokes and or losses oil still then the head will be off for a good inspection and take it from there.
Thanks for all the comments and advice so far, which has been appreciated and helpful.
Andy
-
Broken oil ring on the RHS would appear to be the problem. Ironic that it was the RHS that was originally smoking and that was the same side on which part of the oil ring has clearly been broken during the re-build, sods law.
No damage to the bore, so just a overall check of all the valve and bore clearances whilst it is apart and then put it back together hopefully now smoke free?
-
Good to hear you have found the problem *smile*
Peter
-
Sprint, good to see you solved the problem, what brand rings were they?
-
Hi Sprint
I would check the condition / thickness of cork washer in the breather in the timing cover.
Anji