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B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 11:34 am
by csx355
Good morning all - a little while ago I aquired a BSA motor that had been used for speedway in the Home Counties by two brothers. The motor had been left in a garage along with a spare much modified head and some other bits and bobs. The motor has no engine numbers and does not appear to ever had one - It is an end fed B44/ with alloy head and barrels that have been subjected to a very tidy fin job. The motor has been bored to 84mm (500) and gas flowed (ported with big valves). There are some odd drillings on the cases which I think may be additional breathers along with steady mounts above the rear frame mount. It has also been converted to run a magneto and was fuelled on dope. It came my way in a sorry state and I felt it would be fun to rebuild it (it was seized solid through time) and maybe soften it somewhat, run it on petrol, fit an Electrex ignition / lighting system and put it in a road going frame.

Any way having stripped, cleaned, tapped and tidied up the casings a la Rupert Ratio, fitted all new bearings and seals I decided to clean out the crank sludge trap that was absolutely jam packed. Although the bottom end was good I was worried that I may have dislodged some of the gak so sent the crank to Alpha for stripping and cleaning - Result a unit new Alpha bottom end - total peace of mind and an eye watering hole in my wallet!!

I have just done a trial 'dry' build using the original piston in order to find out what bits might be needed prior to final assembly. I have a new piston for the final build. Everything has gone together very well but on rotating the motor without the head bolted down and without push rods - the push rods that the motor cam with do not have the end caps - the piston lifts the head by 5mm. This would possibly explain the hand made compression plates that came in the box with the motor.

My dilemma is how do I ascertain the correct height for a nice new compression plate and in turn the push rod lengths. Do I just keep spacing until it clears? What about Piston to valve contact - could I use / make dummy alloy push rods until it all works on the bench? How much latitude over and above should I allow for a running engine?

I am sure that someone here has been through all this before but a little guidance from experience would be gratefully received.

Many thanks in advance.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 11:57 am
by minetymenace
I assume your new and old pistons the same dimension. I think I'd go trial and error method. Fit the plates to stop the head lifting. With no push-rods, a burette, verynear calipers and a calculator, work out the Compression Ratio, the adjust the thickness of the plate to give your desired CR. Not knowing what cam you have, I'd then fit the push rods and check the piston/valve clearance with a blob of Plasticine adding thicker plates if necessary. Measure the CR again, and if this looks good for petrol, go for that.

What frame is it going in?

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 12:38 pm
by csx355
Hi MM - thanks for the reply - there are no markings on the original piston crown so I am going to have to measure it and the bore to ascertain whether it is standard or oversize. As I was always going to use the new or a new piston I wanted to get everything sorted first before waltzing off to an engineering shop.

I have not used any gaskets in the build so I will allow for it by using an old head gasket next time, this was just an initial walk thru.

I'm guessing that I don't need to fabricate complete new comp plates each time. Could I just use spacer tabs under the barrel and make a final plate when I get the required clearance.

Burette - god I have not heard that term used since my days in a Milk Board Lab. Could you explain - why am I checking the volume? I'm guessing it's to work out the CR but could you explain how? Please assume that I am a total engineering numpty.

I managed to get a Starfire frame that has the narrow rear engine mount. I have had it shot blasted and powder coated clear showing off the brazing. I also have a nice little alloy fuel tank along with a vast array of oil tanks to choose from. Newly chromed shuttle valve forks with exposed springs. Alloy front and rear guards and a high level pipe. Basically a high and wide Street Moto predominantly black and polished alloy. It's not going to be original or anything like it but I thought that it might make a decent, fun little commuter with minimal fuss. Well that's the plan.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 2:09 pm
by koncretekid
I didn't know it was possible to bore the B44 barrel out to 84mm. I've seen a B44 cylinder that someone bored and fitted an 84mm sleeve, but they used a sleeve that was too big on the outside (probably a B50 sleeve) which half closed the cylinder stud holes so was never used. It's still sitting on a shelf in the basement of British Cycle Supplies in Nova Scotia. Maybe they intended to drill the stud holes out afterwards but couldn't figure out how to do that with the inside iron and the outside aluminum. In any case, the inside ID of the stud holes in a B44 head is about 91.5mm, so an 84mm bore would leave only 3.75mm wall thickness for the sleeve. I guess it works until it blows. But measure the bore carefully, because if it is worn more than 6 or 7 thousandths, you may have trouble getting the rings to seat and an overbore might be tricky.

Is there still an fire ring at the top of the cylinder which protrudes into the head? Do the head gaskets seal on the surface or in the fire ring recess, i.e. just a copper ring? If there is no fire ring projecting into the head, then the head gasket has to seal on what's left of the surface between the stud hole and the bore - - not much surface there. If that is the case, then the top of the piston may be relieved to fit into the recess.

You could use spacers instead of a base gasket to get an idea of required thickness. Use modelling clay (plasticine), a ribbon of it on top of the piston in each direction and bolt the head down. You should have about 1mm minimum clearance at the squish area. Without pushrods, you won't be able to check valve clearance, but if you can cobble up some then with the valves adjusted, you should have a minimum of 1.5 mm clearance at the valves after rotating the motor thru the exhaust cycle.

Measuring the compression ratio can be done after making suitable base spacers by locking the piston (with at least top ring in place and sealed with a light coating of grease) at top dead center, head with valves bolted on with a head gasket, and measuring the amount of oil that can be added thru the spark plug hole, if the motor is tilted so that the spark plug hole is the highest point. Fill to bottom of spark plug hole if possible, or to the top of the hole and subtract the volume of the spark plug hole. When you think it is full, tap the cylinder and head all around to help dislodge any air that may be trapped. This is the volume of your combustion chamber, barring the possibility of some air trapped in there somewhere. Add the total swept volume of the motor (499) to this combustion chamber volume and divide this number by the combustion chamber volume to get the static compression ratio. So if the combustion chamber is 60cc, then 559 (499 + 60) divided by 60 equals 9.32. This may not be as accurate as measuring head volume separately, then subtracting piston head volume and adding head gasket volume, but is a hell of a lot easier!

Good luck and keep us posted.


Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 2:21 pm
by minetymenace
I think thismight be helpful. Your engine has been modified to run on dope, and you have to change it back to pump petrol, so reverse all the changed. This will involve changes to the carb, compression ratio and possibly the cam, so I would measure everything to see what you have, decide what you want then set to work....

And everything koncretekid said....keep us posted!

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 2:41 pm
by csx355
Cheers Tom - thanks for that. I will check out the barrel tonight and take some pics.

There is definitely a fire ring, or at least a step where the liner protrudes.

I really have no clue ref the origin of the motor, I'm guessing B44 but as I said it has no engine numbers and has been substantially modified. I did not notice that the stud holes were overly close to the liner - again I will measure tonight. Is there anything else that will define the motor in lieu of an engine number?

Regards Steve

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 4:07 pm
by minetymenace
B44 has single main bearing on the drive side (but it could have been modded), B44 will also have long (I think) splines on the timing side of the gearbox mainshaft. Two or three stud oil pump (three I hope) etc etc

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 12, 2018 4:24 pm
by csx355
Thanks MM - def one main bearing per side - and def only a two bolt oil pump. I have a few pics of the motor as it came to me-


I'm trying to get in touch with the previous owner but as it was laid up for donkey's years he may have difficulty remembering what it was and what's been done.

Fun this - appreciate the time taken to consider it.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Tue Nov 13, 2018 12:04 pm
by csx355
For anyone that is interested in this I have been doing a little more digging into the history of the motor and managed to glean some information from John the chap who sold it to me. It appears to be a tale of two sets of brothers. The fellow that I bought the motor from raced grass track side cars in the mid 70's. His brother bought a complete bike, an Elstar 500, from one of the Banks brothers (Graham and Trevor) that raced Speedway at a fairly competitive level at the same period of time. The motor was fitted to that bike. My guy acquired the bike/motor from his brother and raced it before laying it up in his garage in the late 70's where it has been ever since. . .

So it has not been run for the thick end of 40 years. From murky and distant memory John - the previous owner - tells me that the base motor was a B44 sleeved and bored to 500 - and fitted with Piper hi-lift cams. There are two cylinder heads a fully finned B50 that has had a square exhaust flange welded on, and a B44 head that has been paired down on the fins (very neatly), ported and fitted with B50 inlet valves. Both heads foul the piston unless a minimum 1.75mm compression plate is fitted.

John had some valves machined up to fit but when fitted had issues with head lift !!! This came towards the end of his racing interest at the time and the motor was mothballed as life moved on. Later the valves that were made were compared with the original drawings and it was discovered that the top collet grooves were machined too far down the valve stem towards the valve face. This caused the valve springs to compress too much and go coil bound resulting in the head lift and push rod damage etc.

Given that there are several sets of compression plates with the motor and John had machined several sets of longer pushrods in order to move the head away from the piston. The basic error was in extending the length of the push rods as well and not checking the valves the problem was retained. A good lesson in assumption for us all. The bore and both pistons are std and actually show very little wear which is hardly surpising as the motor has probably done less than 50 (incredibly hard) miles on track and circuits.

As I have said I am only interested in running it as a softly tuned free breathing survivor rather that a high compression fire snorter. It would be good to keep it as a 500 and the Piper Cams are in better shape than the standard set that I have. I'm not entirely sure how this is going to pan out but it will be fun trying. I hope.
Some pics below show the proximity of the Cylinder head studs to the bore - bloody close - you were right Tom, and the piston protrusion with and without a 2.5mm compression plate.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Tue Nov 13, 2018 1:25 pm
by koncretekid
Interesting project. Does the previous owner also have the bike? A few issues I see.

Head gasket: I would contact Ed Valiket who can probably supply some kind of gasket that will sit in the recess in the head to seal on the fire ring. He also sell Cometic gaskets for the B50, but the stud spacing won't be correct for the B44.

Ignition: You could use a standard outer timing cover which might allow you to use a standard ignition, but otherwise you will have to use a crank triggered ignition. I know Ed and others sell these although I have not yet tried one. Then you may loose any possibility of a charging system.

Head lift? I'm not sure what the P.O. meant when he said he problems with head lift. Maybe he meant the piston was hitting the valves, or the head gasket was blowing. But with valves in place, and correct length pushrods, the plasticine method should show up any clearance issues.

Valves: Again, Ed V. can machine different length valves (shorten and re-machine collet grooves) from longer valves, as the standard 5/16" valve shaft size is common to a lot of motors. This should eliminate the coil bind problem.

Cam: Who knows? You will have to put a degree wheel on the crankshaft and a dial indicator on each pushrod to determine cam timing and lift. I make measurements every 10 degrees, but every 5 degrees before and after TDC on exhaust stroke, as that is where you can get valve to piston clearance issues as well as valve to valve clearance issues.

B50 head? The B50 head has wider stud spacing than the B44, so would be difficult to fit, and if you slotted the holes in the head, would you be able to get at the head stud nuts at all? It is certainly a better head as it is taller and has more space to allow larger ports.

I mention Ed Valiket on this side of the pond, but I'm sure there will be someone over there that can perform the work.

Certainly an ambitious project, but when finished, will be a real conversation piece.


Re: B44 / B50 Compression plate / push rod advice please.

Posted: Wed Nov 14, 2018 3:43 pm
by csx355
Thanks Tom - the previous owner called the 'other' head with the welded on square exhaust flange the 500 head although it has the same cast number as the one in the pics.

Ref the ignition - I'm thinking along the lines of this Electrex kit with the small charging option for a capacitor or small battery to use basic lights. I have a complete points side cover.

Ref Head lift - Pretty sure that he meant that as the valves opened,but before fully open the valve springs were compressed to their limit making the pushrods push against essentially fixed rockers and lifting / trying to lift the head. I would have thought that the push rods would have bent but he did not elaborate more. Plasticine and alloy bar stock on order - I smell the onset of Lathe time in the garage, wish I knew what I was doing!

Ref Head Gasket / fire ring seal - I have to admit to being totally out of my depth here - I'm guessing that I would need to use both on the motor with the ring sealing the fireworks inside the cylinder and the gasket simply acting as an oil seal between the head and barrel - or am I missing something?

Ref Valves - are the B50 valves longer as a result of the deeper head? If not, I'm not sure why I can't just buy an off the shelf B50 inlet valve to fill the chasm that has been mined on the inlet side. The exhaust port is smaller and seems reasonably standard. I will measure.

Ref Cam and cam timing - I think that I have the kit and capability to do this - I will report back if you don't mind casting your eye over my readings.

Regards Steve

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Wed Nov 14, 2018 9:39 pm
by koncretekid
I admit that I am a little behind the times in regards the Electrix unit, although I have heard of it. I can't see why it wouldn't work and you could keep your trick looking outer timing cover, like CCM.

Regarding head lift, I don't think pushrods could lift the head. A true B50 head is indeed a different casting number 71/1644 with stud holes about 10mm further apart on the diagonal.

Lathe time, yes, but temporary pushrods made of 5/16" or 3/8" aluminum rod, rounded on the bottom end, probably just drill point on the top to engage the ball on the rocker arm should work well enough to get the info you need. You wouldn't need to use both springs on the valves, just enough spring to return the valve, rocker arm and pushrod and tappet to the cam. With plasticine in place and rotating the motor, you should be able to get a good idea of clearances as required.

I'm not familiar with Piper cams. What is the total lift at the cam (i.e.outside of lobe vs. base circle)?

I'm guessing at the head seal/gasket situation, but that is what I believe will work. You could get some seepage at the gasket joint if you don't get some compression there as oil drains out of the rocker box down thru the small holes in the head and the cylinder into the crankcase as well as along the pushrods. Maybe a standard bored out copper head gasket would work, but I just don't see how it would seal with so little surface area between the fire ring protrusion and the stud holes if the fire ring is not sealed against the head. Isn't that the way the non-unit motors worked? If you can find a copper ring to fit that recess in the head, then even a homemade gasket under the head might be made thick enough to seal the oil passages. There are people who would know, but they're getting pretty thin on the ground anymore!

As for valves, the B50 ones are indeed longer and use a different type keeper (split lock) with a radiused groove. I would think oversize B44 Valves would be available, depending on what your head has been made to use. From your photos, it looks to me like the combustion chamber was welded up and re-machined, possibly to get the higher compression ratio the dope guys could run, something like 17 to 1. It looks like some of the weld is a little rough around the spark plug hole, and I really can't tell what the valve seats look like, almost like aluminum seats? Too bad we're so far apart, cause I'd like to see it up close.

Valve timing: You start at top dead center on the power stroke so both valves are closed. You can do one valve at a time. Actually, it's easier to just set a dial indicator up on the end of the pushrod with the head off, rotate the motor CCW, and take a lift measurement every 10 degrees of crankcase rotation. We usually use measurements starting relative to TDC. so the first 10 degrees is 10 degrees ADTC (after top dead center) etc. until we get to 90 degrees ATDC, then the next measurement is 80 degrees BBDC (before bottom dead center, and then to 0 (BDC) and then starting over again at +10 degrees ABDC (after bottom dead center) to 90 degrees, then 80 degrees BTDC (before top dead center) back to the beginning. Very confusing, but that is the protocol and that is the way most degree wheels are marked. For duration, we usually only start counting at .040" lift until we reach .040" lift on closing. I have done this for several cams and posted this info on this forum in the Tech section.

Of course you have to pull the inner timing cover to see just how the cam gear is set up relative to the crankshaft pinion. When pulling the inner timing case, make sure you hold your thumb on the end of the cam as it can come off with the cover if you don't. Then you would not be able to see how the cam was set up. If you do this, take a picture before you pull the cam to see how the PO had it set up. If he used the tab washer on the crank pinion, you might not even be able to see the timing mark until you bend the tab out.

As you can see, I have far too much time on my hand. It's quite a nasty freezing windy day here, too cold to work in my outside shop, power out for four hours, back on now so internet is working again.


Re: B44 / B50 Compression plate / push rod advice please.

Posted: Thu Nov 15, 2018 10:57 pm
by koncretekid
I forgot to mention that when degreeing your valve timing, you have to rotate the crankshaft two complete revolutions to complete the cycle.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Fri Nov 16, 2018 8:57 am
by csx355
Thanks Tom - I have had a 'rest day' on the motor today as I am waiting for some bits and bobs to arrive before proceeding further, plus some of my other girls were needing attention - the usual sort of stuff - lighting failure on my way home from work due to my T140 rear lamp hanging off. Nothing too serious when it's pitch black and raining!! I also took the time out from the motor getting the frame prepared - head stock, forks, shocks etc. It's good to shake it up a bit.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Nov 19, 2018 1:26 am
by csx355
Well that was a peculiar day - all revved up to get technical on the motor, early start, pull the bikes out to make some elbow room in the garage and end up having to spend the next 2 hours repairing the centre stand on the Bonneville. Not what I needed or planned. But it will teach me not to start my bikes on the centre stands.

Anyway some measurements, observations and questions -

The fire ring - I take it that this is just the liner protrusion from the barrel, not like a fire ring that would be manufactured from copper wire and tapped into a recess. If so mine protrudes above the machined face of the barrel by 3mm.

The head recess that the fire ring sits in is 2.5mm deep - is this too shallow for the barrel protrusion ?
The O/D of the head recess and the barrel protrusion is 88mm
the I/D of the head recess is 83mm
The liner protrusion is 2.5mm - maths Eh?

Given that I am going to need and would like to use a base plate to lower the compression ratio, softening the motor and to give piston to head clearance is there any reason why some of this spacing can not be done at the head using a thicker head gasket. I'm thinking if I have a lazer cut copper seal made measuring 88mm od x 83mm id x 1mm thick to sit in the head this will give me a head gasket gap to seal of 1.5mm plus an allowance for compression both at the fire ring and the gasket. And that's where I become unstuck. How thick should this 'extra' allowance be. Too thick and the fire seal will not be compressed - too thin and oil will leak from the head.

If I am barking up the wrong tree please let me know as it's possibly that I could end up trying to find a standard 441 barrel.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Thu Jan 31, 2019 8:13 pm
by csx355
Hi all - not really sure if I should continue on this thread or start another. Anyway here go's.

Quite a bit has happened since my last post - firstly I decided that I was building in a significant amount of problems with the 500 barrel. Problems that would need solving beyond my pay grade so I decided to source a used 441 barrel and piston that appeared to be in excellent order. It came from the states at a very reasonable price but took some time to wing it's way to the UK, turning up just before Christmas. The barrel and piston are plus 40thou and both are very good.

Christmas and the New year came and went, (family time) and then I managed to get the motor built and fitted in the B25 frame that I acquired for it. I fully built the motor on the bench and everything seemed pretty good to me. If I had any reservation it was about the oil pump which was the original alloy two bolt affair that I lapped the faces in and it was reasonably smooth but there was just a little niggle in my head about it. I set the valve rocker clearances al la Rupert Ratio and all seemed fine.

Hooking up the fuel she started up after four or five kicks with my new Electrex ignition / lighting coil doing the job as it should. The oil return was not brilliant but having read that the roller big end does not give any back pressure I was happy with it. The motor sounded ace and picked up well responding nicely to the throttle and ticked over smoothly. I kept watching the oil return - call me paranoid but I swear each time I started it the return flow got less. I couldn't live with it so having bought a 21" front end from one of the members on this forum I also relieved him of a cast iron three bolt oil pump. Having resigned my self to stripping the motor again I got down to it. The new oil pump was smooth and confidence inspiring and having the cases off I double checked the oil return valves, pressure relief valves and fitted new springs that I hadn't done first time around.

I fitted the motor back into the frame without the head and rocker cover and set about checking the rocker clearances.


I can't set the exhaust clearance as the pushrod falls off the rocker. Same push rods - same rocker box cover same cam - which by the way is a standard B44! If I close down the clearance the adjusted is set so far in there is no room for the lock nut AND the motor locks when turning by hand. What the hell is going on?? It was cold in the garage today and I am probably not thinking straight but I was 3 hours messing with this and in the end I just had to walk away - any thoughts anyone ?

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Thu Jan 31, 2019 11:24 pm
by minetymenace
With the weather you are having down there, I'd light the fire and crack open some HSD. Sticking valve maybe....

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Fri Feb 01, 2019 12:02 am
by csx355
HSD - high speed death

1st pint doesn't touch the sides
2nd pint makes you loud
You don't remember anything after three!!!
I'll give the valves a little wake up tap - it's possible.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Fri Feb 01, 2019 12:36 pm
by csx355
minetymenace wrote:
Thu Jan 31, 2019 11:24 pm
Sticking valve maybe....
Doh! that's so obvious! It might also explain the mechanical 'ding' that I heard. I will whip the head off and check the valve in it's guide. It was cold in the garage and that might explain it binding particularly if it was fractionally tight on the first build. I'll get a new valve lined up.
Thanks for that.

Re: B44 / B50 Compression plate / push rod advice please.

Posted: Mon Feb 04, 2019 11:23 am
by csx355
So here's the lil booger - not just stuck open but the devils own job to get out. I didn't want to damage the insert so I heated the area and slowly out she came. The daft thing is that when I put the valves in and lapped them they were not tight. Which begs the question - What caused the seizure? Has to be poor oil flow to the valve gear - so perhaps my hunch that the return dribble was insufficient was correct. Phew a close call I think. There was a raft of homemade valves that came with the motor all used and some in pretty poor condition. I picked the best of them - that will teach me to economise! I suppose it's possible that the valve stem was fractionally oversize.

Hopefully the iron oil pump upgrade - new valves and new oil pressure feed spring will sort it all out. If a jobs worth doing - it's worth doing at least three times!!

One other thing that someone might be able to throw some light on. My pushrods are both the same length and measure 8 and 3/8" overall including the caps. Measured with a steel rule, shakey hand and milky eyes! The book states that they should be 8 5/16" so mine are potentially a 1/16" longer. Could this be contributory? I cant find any reference to push rod length being measured with or without end caps Is this difference compensatable with the tappet? The motor was much modified so returning it to some form of standard for road use is turning out to be fun.