Author Topic: ignorance is bliss  (Read 1117 times)

Offline mike667

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ignorance is bliss
« on: 27.11. 2009 21:50 »
well after spending my first riding season with my A10, and thoroughly enjoying it for some 2500 trouble free miles (pretty good considering it is one of my 5 bikes) i decided to get it prep'ed for winter time with fuel stabilizer and fresh oil. While putzing around i decided to do a compression test on it - should of known better - showed 115 in first cylinder (great!) and then barely punched 90 in the other (YIKES!) -damn- oil down each pipe raised the pressure to damn near 145 in each - arggghhh *eek*. Weird as it never fouled a plug, they didn't look oily,  and she ran sweet ..... oh well guess i have something to do over the winter now -  if i can get the head and barrel off before it gets any colder - really shouldn't be to surprised as motor has got about 14K  on it now

 is there anything i should particularly  look at or  poke around upon in the bottom end while tops off ? didn't seem to be making any strange noises etc so hoping the bottom end is fine -  thank goodness i can't run a compression check on it!

mike




Online groily

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Re: ignorance is bliss
« Reply #1 on: 27.11. 2009 22:42 »
People will and can shoot me for saying it, but I'm not totally convinced by some of the compression tests one can do, especially if with one of those things with a rubber bung on the end. There are so many variables - hot, cold, oily, dry, etc. Hot and oily is best maybe, with throttle well open (well,that's what some unused gizmo hereabouts says on it).
I spent an interesting half day a few weeks ago with the relevant gauges off an old 'Sun' leak tester (and a compressor to pump it up) in a friend's shed. The 'results' dictated a head overhaul on one bike (ex valve leakage), a bigger engine rebuild on another (where the leakage seemed to be past the rings rather than a simple valve thing) and a blown head gasket on a vintage car (leakage between Nos 2 and 3 cylinders). We turned up a dummy spark plug and adapter to get round the rubber bung problem: better, but there were still 'leaks'. Not huge, but leaks nonetheless.
Not doubting at all what the toy told us - eyes to see, gauges can't lie, etc. The question was - what difference would it make?
Subsequent Expensive Head Job (valves, seats, guides, springs and so on) on first patient (a very well-maintained 500cc single not of the marque) made no noticeable difference to performance in any way (it ran pretty darn well before), and the jury's still out on the others, which were also running well.
Reckon he regrets ever having plumbed the thing in!

If it isn't breathing heavily, using oil, running like a lame dog, oiling up etc etc, personally I'd keep on running it until something actually reinforces the diagnosis. I absolutely refused to plug my A - which is what I was on that day - into the thing, as I reckon it was and still is running fine.
I may be totally cavalier and courting trouble and future expense, but . . . If it ain't broke . . . .
Bill

Offline Beezageezauk

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Re: ignorance is bliss
« Reply #2 on: 28.11. 2009 11:17 »
Hi Mike,

I'm with Groily on this one..... but if you do decide to pull the head and barrel off I would give the camshaft and cam followers a visual check for wear, plus a check on the big end bearings.   

These engines run quite well with a certain amount of wear and the only thing to be aware of is burning oil, knocks and excess rattles such as tappet noise.  Even tappet noise can be acceptable as long as it's not too much.  At least if you check the camshaft and followers it will tell you if the engine needs immediate attention or just something to keep your eye on in the future.

I'm sure you will find nothing wrong with it otherwise you would have checked it out earlier.  Lets face it...you had no reason to do a compression test other than your own curiosity.

Yeah, I'm with Groily.  If it aint bust....don't fix it!!

Beezageezauk     

Offline mike667

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Re: ignorance is bliss
« Reply #3 on: 28.11. 2009 11:40 »
Good advice,  Groily and Beezageezauk   -  yes curiosity got the best of me, i don't think i'll do any more compression testing on my bikes that are running good!
 - I think i'll end up just riding it leaving it as is and contemplating it after/during another full season of riding it - like you guys said if it ain't broke don't fix it - only reason i even gave it a little thought was I may be able to redo the top end, ride it for another 10K or so then redo the whole engine as opposed to redoing the top end farther down the road and not getting any real miles before the bottom needs attention....  especially since  i remember reading somewhere on the web (for what ever that's worth) that the A10 bottoms are generally good for about 22-25K if not thrashed and with frequent oil changes

thanks again!

 Mike

Online chaterlea25

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Re: ignorance is bliss
« Reply #4 on: 28.11. 2009 18:56 »
Hi Mike,
Before diamantling anything serious, have you checked the valve clearances???
Maybe you have a tight tappet??
or even a sticky valve in a guide??
HTH
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline mike667

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Re: ignorance is bliss
« Reply #5 on: 28.11. 2009 19:42 »
Hi Mike,
Before diamantling anything serious, have you checked the valve clearances???
Maybe you have a tight tappet??
or even a sticky valve in a guide??
HTH
John O R

 Hi John - good thought  - i adjusted them recently, and while i haven't checked them after seeing this problem, adding  oil to the cylinders and seeing a large increase in my readings  suggests my rings are probably worn (though i bet the valve are not the greatest too)
thanks!

Online groily

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Re: ignorance is bliss
« Reply #6 on: 29.11. 2009 00:19 »
Not wanting to start one of those 'I've done 3 million miles and never a problem' sort of threads, but 22-25K miles per bottom end job seems a bit thin to me Mike. I really don't know, but I can't see why a well-screwed together engine in a mild state of tune couldn't do double?
I expect, and have had several times over, 30-40K minimum out of twins of a less robust nature than our BSAs, and have done a good 20K on the bottom end of the A I've got. It had presumably done a few miles already as it didn't come to me with any claims to being 'newly rebuilt'.
(It'll probably run a big end this week now.)
Bill

Offline mike667

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Re: ignorance is bliss
« Reply #7 on: 29.11. 2009 22:57 »
Not wanting to start one of those 'I've done 3 million miles and never a problem' sort of threads, but 22-25K miles per bottom end job seems a bit thin to me Mike. I really don't know, but I can't see why a well-screwed together engine in a mild state of tune couldn't do double?
I expect, and have had several times over, 30-40K minimum out of twins of a less robust nature than our BSAs, and have done a good 20K on the bottom end of the A I've got. It had presumably done a few miles already as it didn't come to me with any claims to being 'newly rebuilt'.
(It'll probably run a big end this week now.)

 No i agree 100% Groily - like i said i saw it on the web somewhere (racked my brains trying to re-find it today but never succeeded) that A7/10 bottom ends are typically shot by about 22K - but like most things on the web i take them with a grain of salt. My norton turned 60K and when i tore it apart there was wear, but nothing that would of kept it from chugging another 20K.
On a good note i took the A10 out today - started first kick, as per usual - ran sweet and never missed a beat for the 100 miles i ran about the island. I am going to follow the don't fix if not broken advice until it gets more noticeable -
 thanks again

mike