Recent Posts

Pages: 1 [2] 3 4 5 6 7 8 9 10
11
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by muskrat on 27.02. 2020 10:17 »
G'day Jim.
Another way to tell difference between inlet and exhaust valves is the ex are thicker in the tulip.
Scoring on the TS of both barrels suggests to me the bores aren't at 90 degrees to the crank throw. Meaning the barrels were bored from the head face not the flange face.
As Swarfy says they don't need to be perfect, but it helps!
Cheers
12
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Swarfcut on 27.02. 2020 08:50 »
Jimbo... Your mention of scoring to the bore is interesting, and it depends what you mean by " scoring"  A nasty gouge, smear or  mark matching where a displaced circlip and pin or broken ring have damaged the bore is your worst case, all easy to see when the barrel comes off.
    As it is I think you have it all back together, so you may as well give it a go,  checking first that it all turns over easily with the plugs out and no binding or nasty noises from the valve gear. At least if it runs on one pot, you know where to concentrate your effort. The real test of the valves is whether the compression pressures are anywhere decent. Cam timing can play tricks and overlap means both valves can be open at the same time, you may find your hand over the exhaust is a red herring.

  If the barrel has been rebored relatively recently, a single straight vertical score can simply be evidence of the incompetent so called machinist raising the cutter of the boring machine at the end of the cut, without moving the machine slightly to one side.  Typically a Van Norman boring bar and table set up.

 If it does have to come apart again, regarding  the head, check all the valves are the right size, and get them to seal. As a gut feeling I doubt the seats were adequately recut to match the valves concentric to the new guides. Most engine reconditioners subject valves and seats to a quick vacuum test, and a fault here flagged up.  As the good advice there from Slymo says, get the bores checked and cleaned up with a light hone if necessary. 

 These engines will perform OK without true perfection, which costs a lot. You're almost there, but as mentioned, another machine shop with a different attitude is in order.

 Swarfy.

 
13
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Superflash on 27.02. 2020 07:07 »
Hey Jim.  Cheer up mate.  We all live and learn apparently.  Have been reading this thread with extreme interest as I'm a complete novice at this BSA thing.  Of immense interest was the bit about the inlet valves being magnetic. So I raced off with magnet in hand to check the newly installed valves......and guess where the magnetic ones are  *problem*
14
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by KiwiGF on 27.02. 2020 06:07 »
Ok, so hears an update. BigJim is not a happy bunny so just gonna unload some stuff here then will be taking a break for a bit
Backstory is:- Replacement head purchased, get it blasted, stove enamelled,new cast iron guides,new valves collars collets and springs. First ride cut short, plugs keep coming loose. Head off and scrape out paint around plugs, plugs now do up tight and stay tight, progress, refit head and take for longer ride. loses power when holding at 50 and basically stops but not cutting right out, idles then returns home with less use of the throttle. settings on valve timing,ignition and carb are unchanged from before new head fitted and had been running well. Strip and clean carb, loosen tappets, try again, same problem. Remove head to check valves, bend 2 exhaust valve tops due to poor use of compressor (didn't know about the tap after light tightening, my fault, lesson learned). Walk away. Return with grinder, remove valves carefully. Wash the whole shebang in petrol to guarantee cleanliness, shorten life by a good few years with lung damage. Am reminded from years ago that inlets are larger than exhaust by Swarthy, useful stuff. Take a look at cut exhaust valves and see one is an inlet in size (marked as such on face also. I never checked when i collected it from engineer ( my fault, lesson learned). Steal a new inlet from old head (3000 miles since April) which seems to fit ok, not too much rock, and fit a new (cheap, not the expensive srm type) exhaust valve. Then as i about to fit i notice the vertical scoring on the cylinder wall!!. Only on the timing side but on both cylinders. Think bollocks to this and rebuild the bike anyway. Walk away and open a can and shout and swear for a bit.
Contact engineer today who does not comment when i asked him re inlet valve in exhaust port. Enquire further to check if seats had been cut which is confirmed. Had wondered if inlet had been fitted to exhaust because not enough meat in the head to seat the smaller exhaust valve?
So here's the rub, When i kick over the engine with plugs in and place my hands over the exhaust ports to check compression i can feel a large suction on the induction stroke in both ports, stronger in one, which i assume is the valves not seating correctly. The new cheap one is worst. Have set the inlet and exhaust tappets 2 Thou bigger, could this make a difference?
In conclusion am taking a break from the bastard thing for a day or two. Have been fantasizing about taking the big grinder to it and getting the Mrs to film me and post it on you tube. The bottom end was built by the most expensive engineers i could find ( no names here). The engine has covered approx 3000 miles since April, did have a dodgy cam ring for about 10 of those (my fault). The reason for the replacement head is that i was sold the wrong bolts for the Rocker box and damaged the threads on the old head.
I can predict how the responses, if any, to this post will unfold. Some people just shouldn't be allowed to own a classic bike, and i'm obviously one of those. Call me a " previous owner" and all that entails but please bear in mind i have never owned one of yours.
In th words of the great sage and eminent engineer Berger "thank you for listening, time for a black and tan".

It’s not uncommon to have major issues after an engine rebuild, in my case a solid copper head gasket blew after 600 miles, despite re-faced head and cylinder, so I fitted a new one  *work*. Then before even riding it again, I wondered why it blew and checked my (new) torque wrench for accuracy, it was under tightening by over 30%. This led to a complete strip down to re tighten the big end bolts as I had used the same torque wrench for those  *problem* *problem* *problem*

I have hardly had to touch the engine since though  *smile* (approaching 10,000 miles).
15
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by mikeb on 27.02. 2020 01:50 »
I’d say a few black and tans Jim, and steady on. Maybe it’s some engineers that shouldn’t be near a classic bike. There a bunch on this forum that will feel your pain. It’s not a rational pursuit but a great achievement when we get there as I’m sure you will do. Good advice from Slymo all round. Stick at it.
16
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Slymo on 26.02. 2020 22:03 »
No sometimes jobs just do go pear shaped.

Strikes me that the loss of power was probably a partial seize in the first place hence the scoring on the bores. The valves in the wrong holes are another sign that possibly not all due care and attention was paid by your engineer. If it were mine I would remove the head and check the valve seal by filling the ports with water or meths and seeing what leaks out. If they weep then lap the valves in in the time honored method with grinding paste making sure that you don't spread it around and that you clean it off carefully. You'll know the instant you put the valves back in the guides if you have been careless as the fit will be gritty. Most grinding pastes are water soluble these days so wash it thoroughly with a strong hose and blow it out with air if you have it. The valves should be water tight with finger pressure. It's not a vacuum test but it is pretty indicative. Also if you have a nice full even witness of grey freshly ground surface on the valve and the seat is a similar colour and uninterrupted then you can be confident that the surfaces are mating.

If the bores are damaged the pistons will be too. Pull the barrel off and check the pistons. If they are smeared see how bad they are. If not too bad a gentle relief of the smeared part with a bit of wet and dry should be enough. If the ring grooves are damaged then chuck them. Get the bores checked for clearance and ensure there is sufficient. If not enough then it will need to be honed which will hopefully clean them up. A light hone would be a good idea anyway just to clean them up and new rings is a good call because they can loose their temper and shape after a seizure.

Above all find a new engineer. Some engineers simply don't take small jobs seriously and hand them over to apprentice staff to muck about with. If they aren't supervised properly the misery is all yours.  We had an aircraft rated engineer leave a lock pin out of a crankshaft on an old Riley 9 once and the motor wrote itself off a few months later. Always thought it was lucky we weren't in a Cessna.

Good luck and keep at it. 
17
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Greybeard on 26.02. 2020 21:24 »
What a bugger!  *sad2*
18
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by BigJim on 26.02. 2020 20:47 »
Ok, so hears an update. BigJim is not a happy bunny so just gonna unload some stuff here then will be taking a break for a bit
Backstory is:- Replacement head purchased, get it blasted, stove enamelled,new cast iron guides,new valves collars collets and springs. First ride cut short, plugs keep coming loose. Head off and scrape out paint around plugs, plugs now do up tight and stay tight, progress, refit head and take for longer ride. loses power when holding at 50 and basically stops but not cutting right out, idles then returns home with less use of the throttle. settings on valve timing,ignition and carb are unchanged from before new head fitted and had been running well. Strip and clean carb, loosen tappets, try again, same problem. Remove head to check valves, bend 2 exhaust valve tops due to poor use of compressor (didn't know about the tap after light tightening, my fault, lesson learned). Walk away. Return with grinder, remove valves carefully. Wash the whole shebang in petrol to guarantee cleanliness, shorten life by a good few years with lung damage. Am reminded from years ago that inlets are larger than exhaust by Swarthy, useful stuff. Take a look at cut exhaust valves and see one is an inlet in size (marked as such on face also. I never checked when i collected it from engineer ( my fault, lesson learned). Steal a new inlet from old head (3000 miles since April) which seems to fit ok, not too much rock, and fit a new (cheap, not the expensive srm type) exhaust valve. Then as i about to fit i notice the vertical scoring on the cylinder wall!!. Only on the timing side but on both cylinders. Think bollocks to this and rebuild the bike anyway. Walk away and open a can and shout and swear for a bit.
Contact engineer today who does not comment when i asked him re inlet valve in exhaust port. Enquire further to check if seats had been cut which is confirmed. Had wondered if inlet had been fitted to exhaust because not enough meat in the head to seat the smaller exhaust valve?
So here's the rub, When i kick over the engine with plugs in and place my hands over the exhaust ports to check compression i can feel a large suction on the induction stroke in both ports, stronger in one, which i assume is the valves not seating correctly. The new cheap one is worst. Have set the inlet and exhaust tappets 2 Thou bigger, could this make a difference?
In conclusion am taking a break from the bastard thing for a day or two. Have been fantasizing about taking the big grinder to it and getting the Mrs to film me and post it on you tube. The bottom end was built by the most expensive engineers i could find ( no names here). The engine has covered approx 3000 miles since April, did have a dodgy cam ring for about 10 of those (my fault). The reason for the replacement head is that i was sold the wrong bolts for the Rocker box and damaged the threads on the old head.
I can predict how the responses, if any, to this post will unfold. Some people just shouldn't be allowed to own a classic bike, and i'm obviously one of those. Call me a " previous owner" and all that entails but please bear in mind i have never owned one of yours.
In th words of the great sage and eminent engineer Berger "thank you for listening, time for a black and tan".
19
hi Mt
While the engine is apart measure the timing side crank and bush, ideal clearance is 0.0015in. worn out at 0.003in.
Inspect big end bearings and clean the crank sludge trap
Check the pressure relief valve too, and wash out all the oilways
The cam and followers are the first parts to suffer when oil pressure is low
Maybe you just dodged a bullet?

John
20
G'day Mt.
Theres your problem. The cush nut should be done up to 65 ft/lb. I use the Citroen tool ( https://tinyurl.com/uea2y3z ) and an air rattle gun set on 4. The un-worn followers will be fine on a new cam. The 356 will be better for you.
You will need to establish the size of the new shim stack (one is best or the least number to get the size). Which means putting back together without any shims and checking end float then stripping down again to insert the shims behind the bearing. A bit of work but worth it.
Cheers
Pages: 1 [2] 3 4 5 6 7 8 9 10