Advice needed - engine tightening up - help - tips

[nigeldtr]

Guys,

Well got the head and barrels off this evening and as suspected piston seizing on one side. The engine has obviously been rebuilt recently bottom end in lovely condition and cams also look good - may need new followers. To the main point - I have tried to measure the bores accurately as I can with good old analogue equipment and the good bore seems to be 2.817 and the "bad" one 2.814. Piston seems to be 2812, which seem to be a be too tight for comfort - or free running!

What a shame one lovely new piston and one scuffed up - looks like some time is needed  with some wet and dry on the lathe and off to get the tight bore honed out a bit - I assume the pistons must be about +060.

Brian's descrition:

"When this happens the motor will usually restart almost immediately. I had it happen many times in my racing days and if you are quick enough you can pull in the clutch and coast for 50 yards or so and then let the clutch out and the motor will restart."

was spot on!! well done.

Back to the cam followers if I remeber correctly, these should have a nice round profile rather than triangular?

Thanks for all the feedback etc. great to read and follow.

Nigel

[Richard]

Nigel
I am glad it is not to serious at least the cost should not be to much it is just a shame that the people who say they can do this sort of work do not take a bit more time and get it right the first time, as for the followers if they are not to worn they can be reprofiled as were the ones in my S/R.
I bought new ones for my gold flash and suprise suprise there was one follower that I had to rub down on a stone on one side to get it to operate without binding up, again the curse of pattern parts, given the choice I would rather have the original ones reprofiled which is what I intend to do with the ones I took out.
Anyway all the best
Richard

[trevinoz]

I had my followers ground to the correct radius and had them heat treated to harden them.
Trev.

[nigeldtr]

Some pictures of the good and the bad!!

Out of interest, I popped a top compression ring into the bores and squared it up with the good piston and found that with the same ring the ring gap was 0.041on the good side and 0.031 on the bad side that would indicate the "smaller" bore is actually about .003 smaller. which seems to tie up with the measurements. Bad news is that it seems to me I have +050 ring in what should be +060 bores? What a shambles!

Will be taking all the bits over to a local company to measure up and hopefully repair. They said they can also reprofile the cam followers for me.

PS pitons are +060!


Regards

Nigel

[RichardL]

Nigel,

Wow! those followers are truly in bad shape. I will be interested to hear from Trev, or others, if the wear on yours is not, acutally, beyond refacing. Remember, everything taken off the follower face must be made up in the valve adjuster, which leads to further questions: Is there enough range in the adjuster screw to accommodate the change in follower length?; Even if there is enough range, does the angle of incidence between adjuster and valve become an issue? Considering you must still pay for the refacing, maybe GBP 93 for a new set from SRM is a good investment.

Now, considering the wear on the followers, what is the condition of the cam and other parts in the valve train?

With the piston scoring, I would not try to remove all traces of it. Rather, just take down the high spots. You probabaly don't want to adjust the piston fit by reducing the diameter of the piston. Instead, make the correction through honing.

Regarding the rings, doubtful you have a +50, as I don't think such were made. More likely a +60 improperly gapped. Get a new set to go with the rehoned cylinders. I have a set, but I'm not trying to hawk them here. I don't think you will have a hard time finding them all over the UK.

Regards,





Richard L.

[Richard]

Nigel
When I saw the picture of the cam followers my first words out loud were Bl**dy H*ll I think I would agree with Manasound. My thought seeing the picture is why have they worn so badly or has someone done a hatchett job reprofiling them on a grinding wheel.
What is the camshaft like as surely with those cam followers some abnormal wear could have been caused to it.
£93 seems a lot to pay for cam followers even SRM ones, there are other sources in the uk that would have followers at less cost and possibly just as good, or look around for some genuine second hand ones that are better than those to be reprofiled if needed. More than likely there will be others like me that replaced perfectly good followers in the quest for a quiter motor only to find out it was not the followers rattling
All the best
Richard(Minety UK)

[nigeldtr]

When I lifted the barrels off, I looked at the camshaft and it seemed pretty good. At that time I had not seen the followers! Seems to me that the camshft was replaced recently along with the bottom end. Don't understand why the old followers are in there? The surfaces are a little scratched on the cams but not surprising considering the state of the followers. Anyway replacements will need to be found.

Are all rings the same? little concerned as the pistons seem to be "no name" and don't know if the grooves will match new rings etc - any exerpience here?

Nigel

[Richard]

I have never had to buy just rings as when mine tightened up it pinched two of the rings in the grooves and although the pistons were not as badly scored as yours I bought new ones with rings (80thou) and decided to keep the old ones as good spares in the case of an emergency.
I since managed to remove the rings intact and then cleaned the ring groove out in the lathe. I would think that the pistons were machined to a standard as when people buy rings they try to get heppalite no matter what make of pistons they have so that would suggest that the rings are only in a standard width so to speak.
Richard

[RichardL]

I've no intention of setting myself up as the best expert on this, but the cam looks worn with scoring and also looks a little like the ends of the lobes might be wavy, which seems to be indicated by the three parallel lines of light across the lobe thats pointing upwards. Also, it does look a bit like the lobe ends are not even across the width of the lobes. If I could drag my fingernail across the scratches and get a noise, that seems like more scoring than one would like. On the other hand, it might just run fine for thousands of miles after the followers are replaced. It looks like there is oil in the gallery, so we might assume it was not running dry, at least, not recently.  I won't be surprised if someone chimes in and tells me to stop waffling about the cam and just say it outright!  OK, here goes, the best thing would be a new cam (maybe that's still waffling a little, but it's not my money and time).

In as much as you might easily justify a new cam (with the bike, not necessarily with your wife, if you have one), replacing it would give you the added advantange of being able to check all oiling paths including cleaning out the sludge trap. Someone less than totally careful worked on that engine. You don't necessarily have to assume that everythng is wrong, but checkng out the few things that can really sink you would be worthwhile.

Richard L.

As for the rings, if the pistons are made for an A10, I am rather certain that rings identified for an A10 will fit the width of the grooves. Your's look completely normal in that regard. If it truns out that they are gapped properly, you might just reuse them.

Richard L.

[A10Boy]

For my two pen'orth that cam looks fine, they all have some kind of witness marks from use.

Unless of course you want perfection, if you do, I'll give you a couple of quid for the old one, but a new one would look like that after a few thousand miles.

[chaterlea25]

HI Nigel,
I hav just joined the forum, but am a longtime BSA owner, restorer/repairer
The root cause of your problems is the oil pump I rekon!!!
OK so heres my experience of this type of failure, (not on my bikes though )

1)low oil pressure due to bad, or porus pump body, worn timing side main bearing, or to tight bearing which has siezed on the shaft  and the bush is turning in the steel sleeve!!

2) With low pressure the pressure relief valve does not open to bypass oil to fill the trough that the cam and followers run in. this leads to worn followers and eventually wrecked cam.
On BSA twins the first sign of problems is rattly tappets

3) Lack of pressure to the drive side big end, the rod should have a little bled hole in it facing up towards the piston, lack of oil leads to the left side piston siezing, then the rod breaks and wrecks the crankcases!!!

My advice to you is that you will have to strip the engine completely as there is now a lot of very nasty bits of cam follower in every concievable part of it, in oil tank, pipes and everywhere!!!!

A lot of owners complain about wet sumping on A7/10 engines, in my experience this is more often caused by the porus nature of the mazak (zinc alloy) that the pump body is made from
and or a little wear on the pump spindle which lets the oil leak past
anti syphon valves dont help here because the oil leaks out of the pump and then there is no prime in the pump to lift the anti syphon valve!!

My Super Rocket has modern pistons and runs at less than the original BSA specified clearance
and I have not had problems over 8000 miles,

I know an A10 owner who rebuilt his engine because the followers/cam were worn, new T/S main bush and bigends mains etc, it tightened after 50 miles or so but freed out again so he rode on, a couple of hundred miles later it blew up in a big way, breaking the drive side rod, holing the cases and wrecking the cylinder!
The cause of this was the oil pumb body was porus and the oil just leaked through the alloy, this is then picked up by the scavenge side of the pump and returned top the tank, showing normal oil circulation!

Apologies for being so long winded but there is an awful lot of mis information floating about
Regards
John O R

[A10Boy]

Hello John, welcome to the forum.

My A10 had a really good return to the tank, despite the TS bush having 12 thou play when I stripped it, I think most of the oil pressure / flow was going out of the bush, its a good job its got a good pump.

[nigeldtr]

Hi Richard,

I have run my nail across the cam and although not perect, I will leave it in and buy new followers. I will probably do max 1000 miles a year and at the end of the day, I bought this to ride and not rebuild.  Hopefully I can get her back together in the next couple of weeks and enjoy riding around the country lanes. Still need to get the battery charging - next action point!!

I have the tendancy of being a but of a perfectionist and if I take the engine out then I may as well repaint the frame, and the tin work and fix the crome, I am sure you know what I mean.

John, Thanks very much for your input here as you will see form the above notes, the bores are not right and running the good piston in the bores, there is actually a tight spot about halfway up on the side where it seized. If I have to strip the engine, I will never get it put back together as I have no time, so option is clean things up improve what I can and put her back together - I will have a close look at the oil pump etc and the piston oil holes in the conrods. If she throws a rod then you will probably see it on ebay for spares but lets hope it doesn't!!

I don't know much about suppliers being here in Germany, where can I get all the bits from?

Nigel

[RichardL]

In Austria, www.vintage-motorcycle.com
In Sweden, www.basmotor.se
In the Netherlands, http://www.petersclassicbikeparts.nl/index1.html (maybe)
Of course, many in UK:
www.draganfly.co.uk
www.srm-engineering.com
www.burtonbikebits.net
www.canddautos.co.uk
www.leighclassics.com

And the list, no doubt, goes on. I can't say I've heard of any in Germany, proper.

I understand what you mean about riding it rather than working on it, and removal from the frame is a much bigger commitment. It would be nice if oil could be forced through the crank such that you could watch it ultimately emerge from the tiny hole in the left rod. I think the how-to on that was covered here once, but I can't remember where or when. Checking or changing oil pumps is a much smaller commitment. However, I am having trouble envisioning enough porosity in the casting of the pump body to represent a leak, as suggested by John.

Richard L.

[nigeldtr]

Hi Richard,

Bingo! well I just tried holding the rods and pushing up and down and I managed to get the flywheel spinning and could see oil coming out of the oil hole!! so it coming through - what a relief. Obviously can't tell if this is enough but it is coming through.