The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Tukig on 07.02. 2012 10:59

Title: Cautionary Tale
Post by: Tukig on 07.02. 2012 10:59
Hello everyone,
On a recent ride my 59 A7SS all was well but the motor started to lose power so I took it easy and power came back. Thinking it was a temporary glitch I carried on only for the power to tail off and a horrendous noise to come from the bottom end. The good folk at the RAC took me home. The subsequent strip down revealed that the left hand big end had seized, dragging one big end shell over the other and bending the con-rod. The sludge trap wasn't completely blocked but was quite full, prior to the trip the oil return was good. The timing side bush looked good with no play. The con-rod bolts did seem as though weren't fully torqued up, perhaps this was the cause. The bike did seem to me to vibrate more than I would have expected since I bought the bike, but smooth up to 55mph.
The bike was mainly used for show before I bought it for regular use. So what can be learned? Show bikes are necessarily mechanically perfect despite looking good. If the history of the bike is not known then a strip down to examine the important internals is advised. Finally don't ignore any untoward symptoms to prevent future heartbreak and expense.
The strip down has also revealed worn bores, camshaft and valve train. A major rebuild is now required or, possibly sell as a rebuild project.
I hope this sad tale will provide thought for other riders.
Title: Re: Cautionary Tale
Post by: RichardL on 07.02. 2012 12:07
Hello Tukig,

Similar occurance happened to me after the first engine rebuild I did, knowing nothing, "Huh, what's a sludge trap?" Results very much like yours, but without the bent rod. In my opinion, the engine rebuild is an easier and smaller job than bringing a project bike up to show condition. Additionally, if you get a new bike, you still don't know what's below  unless you buy it from SRM, or the like. Rebuilding your own engine means knowing what's in there and, therefore, having only oneself to blame if things go wrong. Not saying you're laying blame elsewhere, but now you have the benefit of your own cautionary tale, at least that's how it worked for me.

Richard L.
Title: Re: Cautionary Tale
Post by: A10Boy on 07.02. 2012 13:25
It's always a risk when you run an engine that you haven't built yourself.

Loose big end bolts on a failed big end can be missleading, it doesn't mean that they came loose and caused the siezure, they will often be loosened by stretching due to the hammering effect of the failing big end on the crankshaft. If the oil supply is restricted in some way, the bearing "runs" and even properly torqued bolts will be hammered loose as the bearing fails. You were lucky you didnt have the rod break and trash the motor.
Title: Re: Cautionary Tale
Post by: kommando on 08.02. 2012 10:55
The sludge trap wasn't completely blocked but was quite full, prior to the trip the oil return was good.

If the sludge trap fills the oil pressure increases and trips the pressure release valve to dump oil to the sump, which the pump grabs and returns to the tank, so a good oil return only tells half the story. A pressure gauge may give more info as the pressure readings may increase at lower revs, not sure if increased oil pressure would spark the thought of impending doom though ;) .
Title: Re: Cautionary Tale
Post by: Pete Gray on 08.02. 2012 14:43
Is the sludge trap under the sump plate gauze ?
(If I told my missus I was going to clean out the sludge trap I expect she'd tell me not to be so disgusting)
Title: Re: Cautionary Tale
Post by: bikerbob on 08.02. 2012 15:27
Hi there. To clean out the sludge trap you have to completely strip the engine and split the crankcases, then there are 2 plugs in the  ends of the flywheels which have to be removed then you can clean out any sludge which accumulates in the crankshaft oilways that feed the big ends and the timing side bush not a job that should be undertaken if you are not experienced in stripping down and rebuilding a complete engine. However if you have a modern cartridge type oil filter fitted then it is unlikely ever to be a problem or if you do not have a filter fitted if you do oil changes on a regular  frequent basis then you should not have a problem.
Title: Re: Cautionary Tale
Post by: BVSR on 08.02. 2012 15:31
Hi, here You can see one!

Title: Re: Cautionary Tale
Post by: Pete Gray on 10.02. 2012 10:47
Thanks for that guys, I'm just fitting a cartridge filter, a bit late maybe but I'll live in hope !
Title: Re: Cautionary Tale
Post by: BSARoadRocket on 22.03. 2012 06:51
I bought a '47 A7 that I was told had been unused since 1965.  It was one of those bikes that nobody ever spent any money on unless it was an absolute necessity.  If there was any way chewing gum and bailing wire could be used to fix something with out spending more than the cost of the already chewed chewing gum that was how it was fixed.  The front tire was completely bald and the back close to it and both rims bent.  The mudguards and many other parts were butchered and banged up, (it's amazing how badly some people can beat up a bike in just 18 years use) and the crowing glory was a brush paint job.
Anyway much to my amazement the bike still had good spark and seemed to have good enough compression to where I'm sure I could have just cleaned out the tank, installed new fuel line and petrol taps, bolted on a good carb and it would have started right up.

Common sense intervened and I decided that at the minimum I would check check and probably replace the primary chain which is something that is usually in bad need of replacement on an old neglected bike.

One thing led to another and I decided to dismantle the engine to make it easier to perform a weld repair on the primary cases. 

Guess what????  I found all four connecting rod bolts were barely finger tight (glad somebody installed the cotter pins)  and two of the bolts had been replaced with badly stretched, nearly stripped hardware store bolts.   The time was nearing when the engine would have destroyed itself!     It would have been a shame too since the motor was otherwise in pretty nice shape!

It pays to carefully go through everything yourself because you never know what the last mechanic did a month ago or 60+ years ago!
Title: Re: Cautionary Tale
Post by: metalflake11 on 05.02. 2013 17:06
Speaking of sludge traps, if you start with a clean one and change the oil every 1,000 miles or so. With qaulity straight oil and no filter what sort of mileage could you do before starting to worry about it blocking up?
Title: Re: Cautionary Tale
Post by: muskrat on 05.02. 2013 18:51
You won't need to worry mf unless you plan on doing a round the world trip twice. Just clean the sump plate and oil tank gauze now and then.
Title: Re: Cautionary Tale
Post by: metalflake11 on 05.02. 2013 21:15
So you reckon about 50,000 miles then Muskrat? ......Serious question, mines heading towards that and it would be a shame to split the crank for no other reason. I know S.R.M. put one together for a rather eccentric character that had two A10's that he used for despatch riding. He was also a part time inventor and his bikes were full of strange contraptions, some very good and others a bit daft. Well, one of those did over 200,000 miles before failure. Sadly, he became too old or died and they were sold a while back. I wonder if that was the last B.S.A. that worked for a living? The last one I saw was about 20 years ago, An A10 with a sidecar and two guys on a window cleaning round. That was in Levenshulme, Manchester UK.
Title: Re: Cautionary Tale
Post by: kiwipom on 06.02. 2013 02:30
hi guys, is it possible to use an engine flush to clean the sludge trap,cheers
Title: Re: Cautionary Tale
Post by: metalflake11 on 06.02. 2013 04:20
Definately not!  You do not want the loosened 'sludge' running around your engine at any cost. Nice idea though!
Title: Re: Cautionary Tale
Post by: JulianM on 06.02. 2013 07:13

Don't be disheartened you are not the only one to have problems like this and it's well worth it to persevere!

My engine was built by a "Qualified Engineer"  so you can imagine how bad that was  :o)    Rod scrap, barrel split in three etc etc!  I don't think he got anything right!  God only knows what engineering degree he had but it wasn't something even Quickfit Euro would recognize and that's for sure!   He spent lots of money though  *roll*

Good luck and keep on it!

Title: Re: Cautionary Tale
Post by: edboy on 06.02. 2013 07:28
a canadian jim sinclair despatched in london during the 80-90s on a bsa a65 spitfire . with an srm bottom end ,he and his girlfriend kept it immaculate and clocked about 200,000 miles. i last met him around 20 years ago and i believe he was going around the world before settling back in canada.not heard from him since but i hope he and his girlfriend are well wherever they finally settled.
it was fairly obvious even then that for relable motorway speeds or high milage a needle conversion bottom end was the way to go especially as straight oils were becoming expensive and hard to find. now plain old 20/50 is becoming hard to find at the side of the road.
it could be that using straight oil  caused the sludge trap to blockup as after periods of no use it can turn to mud inside the sludge trap.
regarding dodgy rebuilds and sluge traps. why dont you send the lot to srm ? it may be cheaper in the long run.
regards edboy
Title: Re: Cautionary Tale
Post by: wilko on 06.02. 2013 20:33
200,000 miles! That'll be the day! Vincents with 1,000,000 miles. That'll be the day!
Title: Re: Cautionary Tale
Post by: metalflake11 on 06.02. 2013 22:42
Buddy Holly a big influence by any chance?
Title: Re: Cautionary Tale
Post by: gavinoz on 07.02. 2013 00:52
w.r.t. flushing oil, one of the websites says "never use flushing oil, it will wreck your engine in seconds."
30 odd years ago I did, and it did. so don,t! Gav
Title: Re: Cautionary Tale
Post by: gold33 on 07.02. 2013 02:33
I've been very busy lately unraveling the sins of an old fella from QLD who "restored" my machine.
After re-doing the top end (missing valve spring seats worn out valves etc.) and having his "rebuilt" magneto rebuilt I went for a nice 2500 mile ride and have been off the road ever since! Tab washers for the clutch nut are clearly hard to come by up north.

After the clutch fell off at 75MPH on the freeway the fibre drive gear on the magneto lost all its teeth and spread throughout the engine, when stripped down for a clean I discovered the con-rod bolts used are varying sized caphead screws some with washers some without and all of them a loose fit but fortunately torqued within an inch of their lives (con-rods ground to suit the varying length bolts). With the level of quality workmanship displayed on my machine I expected to find the sludge trap to be in a very poor state... but it wasn't  *smiley4* Since I bought the bike 4-5yrs ago I have changed the oil every 250 to 500mile using 20w50 oil for vintage engines from the supermarket, I assume these frequent oil changes are the reason she is so clean inside.
Title: Re: Cautionary Tale
Post by: muskrat on 07.02. 2013 07:33
That's exactly why I rebuild every 2nd hand thing (bike, car, whipper snipper) I get before putting it to serious work. The A65 is the only exception, a fresh top end and hope keeps it going.
At least it didn't have LEATHER big ends Darren. I have even seen that. *eek*