Cautionary Tale

[Tukig]

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.
Gary

[manosound]

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.

[A10Boy]

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.

[kommando]

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 .

[Pete Gray]

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)

[bikerbob]

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.

[BVSR]

Hi, here You can see one!

Markku

[Pete Gray]

Thanks for that guys, I'm just fitting a cartridge filter, a bit late maybe but I'll live in hope !

[BSARoadRocket]

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!