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1948 big bore B33

Hi, I have a 1948 B33 (plunger) which im currently rebuilding the engine, i have over bored and shortened the barrel to accept a wiseco forged piston, the engine was already running a pair of gold star touring cams & ported head, I'm having a hard time finding information on ignition & valve timing using these cams, I've been told standard, but im skeptical as it refuses to start! I know this upgrade was common back then to give the old b33 a bit of pop! Any advise would be much appreciated. thanks

Re: 1948 big bore B33

Use the standard markings on the cams to set the valve timing...At some point you might consider scrambles cams (65-2446 in. and ex.) as an alternative as these are a better option for tuning...

3/8" BTDC will be ok for ignition timing with what you have...To really get them to go the crank needs to be lightened as well but maybe that's for another day....Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

Ian Wright
Use the standard markings on the cams to set the valve timing...At some point you might consider scrambles cams (65-2446 in. and ex.) as an alternative as these are a better option for tuning...

3/8" BTDC will be ok for ignition timing with what you have...To really get them to go the crank needs to be lightened as well but maybe that's for another day....Ian
Hi Ian, thanks for the post, standard it is then. I wanted to get the crank lightened, but was told it would be a difficult task and expensive to do, so I had the original crank rebuild with a shorter rod, as it was the guy took several months to complete the work! I will have to look somewhere else apart from timing to find why its refusing to start!

Re: 1948 big bore B33

myB33
Ian Wright
Use the standard markings on the cams to set the valve timing...At some point you might consider scrambles cams (65-2446 in. and ex.) as an alternative as these are a better option for tuning...

3/8\" BTDC will be ok for ignition timing with what you have...To really get them to go the crank needs to be lightened as well but maybe that\'s for another day....Ian
Hi Ian, thanks for the post, standard it is then. I wanted to get the crank lightened, but was told it would be a difficult task and expensive to do, so I had the original crank rebuild with a shorter rod, as it was the guy took several months to complete the work! I will have to look somewhere else apart from timing to find why its refusing to start!
Ian,the engine is still refusing to start! i note you quoted ignition timing at 3/8 (9.5mm) btdc, I currently have it set to 7/16 (11mm) i wonder if this could be the problem, surly it would still fire?? how critical is the timing on your B33, im wondering if the added compression requires a bigger spark!

Re: 1948 big bore B33

The ignition timing wont make any difference to the spark size! Only when it happens. It shouldn't make any difference to starting it if it's a bit over advanced as you can and should retard it at the lever for start up anyway.

If your valve timing and carb are correct? I wonder if you've timed the ignition on the wrong ramp of the cam plate or indeed a wrong rotation mag? Is it a mag that you've used on this bike before? Ron

email (option): ronpier@talk21.com

Re: 1948 big bore B33

Ron Pier
The ignition timing wont make any difference to the spark size! Only when it happens. It shouldn't make any difference to starting it if it's a bit over advanced as you can and should retard it at the lever for start up anyway.

If your valve timing and carb are correct? I wonder if you've timed the ignition on the wrong ramp of the cam plate or indeed a wrong rotation mag? Is it a mag that you've used on this bike before? Ron
Ron, thanks for your reply, need to get it sorted, my knee's are not up to it!
'I wonder if you've timed the ignition on the wrong ramp of the cam plate' MORE ON THIS PLEASE!!
I've gone over the ignition timing many times, stripped and cleaned the carb (amal 930), still the engine wont even fire!
The magneto ran the engine before the rebuild, the spark is adequate but not exceptional!certainly sparks at the plug with a full kick.
Any other tips or ideas welcome!

Re: 1948 big bore B33

SIlly things first
Are you setting the timing with the advance lever tight or slack ?
On a B it should be slack on an M it should be tight
Check that the cam ring is in fact moving with the cable.
They tend to get stuck if not used for a while.

Next are you 100% sure that the points gap is 0.012" at the highest lift and that the piston is actually on the compression stroke & not on the exhaust stroke.

We have all done that last one before.

Also what plug are you using.
With modern fuels you really need to use a projecting electrode plug.
And an old plug that has been wetted with fuel a,lot will become conductive until that fuel is BURNED OFF.
As you have had the cams out did you manually check the piston travel against valve movement ?

Again you would not be the first person who had timed the valves wrong.

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

Without wishing to teach Granny to suck eggs!!

With regard to the ignition timing. Whether tight wire (cable at rear of mag) or slack wire (cable at front of mag). Set the lever at full advance. As Trevor said, you should see that the cam plate is revolving back and forth with the lever action. (A squirt of WD40 is sometimes all that's needed) and that you have about a 12 thou gap at around the 12 o'clock position.

Set your piston at 3/8 or 7/16 BTDC on the compression stroke (both valves closed, push rods free to rotate). Turn your points block in a clockwise direction until the points just start to open (use a fag paper or I use a 1 1/2 thou feeler gauge). This should happen on the opening ramp at around 10-11 o'clock. Carefully nip your pinion on its taper at this point and then turn the engine over two revolutions until the points just brake open again and check where your piston is.

If it's not in exactly the desired position? Repeat the process as many times as it takes to get it spot on. Ron

email (option): ronpier@talk21.com

Re: 1948 big bore B33

['Are you setting the timing with the advance lever tight or slack ?
On a B it should be slack on an M it should be tight'...]

Both models have 'tight wire' fully advanced ignition pre 1954 and both have slack wire fully advanced ignition post 1954....There is also always the possibility that the 'wrong' mag has been fitted...


There is a very detailed piece on ignition timing in the Technical Section of this site. It covers both the theory behind the timing and the practicalities of setting it...It's worth reading and absorbing that information....

7/16" BTDC is the timing setting for a B31, the B33 is 3/8"...However, as noted in previous posts a discrepancy of that amount won't prevent it starting...

First check you have a good spark at the plug...

Then, following the information in the Tech Section, set your maximum points gap to .012". Next set your piston in the correct 3/8" BTDC position with both valves closed (on the compression stroke) and the adv/rtd/ lever set correctly for fully advanced... Then take a look at the points....If the timing is set correctly the points will just be starting to open with a gap of .001"-.002"...

If this is not he case you will have to reset the timing...Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

now a bit confused regarding timing.

My information (gleaned from a Hayne's Manual so could well be bo**ocks) is B33 7/16 BTDC pre 1955, and 1955-on 3/8.
can anyone confirm or otherwise??

cheers

Pete

Re: 1948 big bore B33

Hi all, many thanks for the tips, to answer some of the questions, its a lucas Mo1 mag, timing set in full advance, cable pulled tight, back plate advances nicely not seized, points set at 12 thou at highest position. I have set the timing by using a depth gauge that screws into the plug hole, turned the engine forward, watch the inlet valve go down, rise, forward till TDC, push rods free to rotate, turn engine back 7/16 11 mm, rotate points cam clockwise to approx 11 o'clock when paper released by points, tighten timing pinion nut on taper. I'm using a champion L-85 plug,the magneto spark jumps approx 4 mm max when using HT spark tester which replaces the plug and earths on engine.
thanks everyone..

Re: 1948 big bore B33

As you have had the cams out did you manually check the piston travel against valve movement ? MORE ON THIS PLEASE!

Re: 1948 big bore B33

[..'My information (gleaned from a Hayne's Manual so could well be bo**ocks) is B33 7/16 BTDC pre 1955, and 1955-on 3/8.
can anyone confirm or otherwise??..']..

Correct...I have always assumed the timing change was due to some change in fuel quality/compression ratio and have always used the later setting...

1949-53 engines used a different piston to '54-55 engines, plus there were alternative compression ratio options listed for various applications...To further complicate things a decompression plate was fitted over this whole period which could be removed to increase compression ratio as required...

Confused?...I am !!...I think it may be a case of shut your eyes and pick a setting...
As noted I've always used the later figure and have achieved good results with that..even with a bike on the dyno and different settings tried...Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

never heard of a projecting electrode plug until now, was using a champion L-85 a nos vintage plug, i will try to find a projecting type plug to replace it.

Re: 1948 big bore B33

A Champion L82C or an NGK B6HS would be the correct plug...Gap to .018"-.020" before fitting....Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

'Carefully nip your pinion on its taper at this point and then turn the engine over two revolutions until the points just brake open again and check where your piston is'

JUST CHECKED THIS, TWO REVOLUTIONS AND IT THE ALIGNS THE SAME

Re: 1948 big bore B33

thanks Ian, will follow that up

Re: 1948 big bore B33

I think i may have found the problem?
I removed the cam plate to double check the cam alignments, i found that the dot on the crankshaft pinion that i used and aligned my cams too isn't at TDC! but the woodruf key is, so i thinking should i have used that to align too instead of the dot?
With the key vertical at 12 o'clock the cylinder is at TDC, but the dot is at 2 o'clock, i think the pinion and its dot is from a later engine??

Re: 1948 big bore B33

No...
Each cam is marked with a dot and a dash...The crank pinion also has a dot and a dash...Turn the crank until the dot and dash on the crank pinion are at approx. 11 O'clock and 1 O'clock....Fit one cam with its dot lined up with the pinion dot...Then fit the second cam with its dash lined up with the pinion dash...That's it...

Both (standard) cams are identical and interchangeable...Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

Ian, thanks for the clarification, seems my pinion is missing the inscribed line for the inlet cam, so it would seem my valve timing is correct.. what a dope!
Another point, I noted from my Haynes manual (1954-61) that the ignition is set in full advance for ALL models with the advance cable SLACK, I have taken some duff advise somewhere because i thought advanced setting was cable TIGHT and setting the timing accordingly.
My bsa workshop service sheet 1954 says to set in advance but omits information on the cable...any ideas/confirmation on this grey area please?..

Secondly, yes there's more!
Apart from the push rods free to turn, is there another way to determine its on its compression stroke?

thanks

Re: 1948 big bore B33

looking at the points end of the magneto, my advance retard cable is mounted on the right hand side, so doesn't it make assumption that a tight cable is full advanced..... correct?

Re: 1948 big bore B33

Yes carb side is tight to advance
Cylinder side is slack cable advance.

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

Trevor, thanks for that.
So, ignition timing correct and valve timing checked, but still reluctant to start, not so much as a cough or fart from it!
any ideas anyone?

Re: 1948 big bore B33

Is there a fool proof way of identify the engines compression stroke?

Re: 1948 big bore B33

Both valves closed and push-rods free to turn. OR turn the engine over in top gear by the back wheel and watch the inlet valve open and then close. As the piston comes up the bore after that, it's the compression stroke. The next time the piston comes up, it will be forcing gasses out through the exhaust valve.

Where abouts are you located? Ron

email (option): ronpier@talk21.com

Re: 1948 big bore B33

Thanks Ron, erm pretty much what I've been doing, this is an odd one,I'm really stumped! Oh well will go through it again tomorrow, re check the already double checked, the answer is there somewhere!
I'm in Essex

Re: 1948 big bore B33

OK! Bit too far for a pop round! I'm in Poole.

Ron

email (option): ronpier@talk21.com

Re: 1948 big bore B33

The engine will run ( badly) if either cam is out by 1 tooth in either direction.
It will do the same if both are out 1 tooth in the same direction
It won't even pop if either cam is 2 teeth out or both cams are 1 tooth out in opposite directions.

At this point in time, I will revive something I have posted before.
A mechanic sought my help because he could not get a customers B33 to run.
It would work fine in the workshop then not even start at the customers house.
There were a dozen or so of these events till he ( not me )worked out it was bad fuel.
The bad fuel went bad because it was dissolving the tank liner so when he drained the tank & put fresh fuel in it at each visit to the shop it would run fine but a week latter the fuel was so bad it would not fire.
He worked this out when he tipped some of the old fuel into his bike and his bike would not start either.

Now confirm the timing .
Pull the timing cover off so you can turn the crankshaft nut with a socket
With both valves closed and the piston at TDC start turning the nut clockwise.
Neither valve should move till the piston gets to BDC when the exhaust ( front ) valve should start to open & remain open all the way to TDC when the inlet should start to open just before the exhaust fully closes.
The inlet should remain open all the way to BDC then close and both valves should be closed all the way till TDC again.

You would not be the first and will not be the last person to time the engine backwards

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

The valve timing is not quite as Trevor describes it with the standard BSA cams (65-2420). For example the exhaust valve starts to open well before BDC at around 65° BBDT and closes shortly after TDC. The figures for cam timings are in the general BSA data sheets somewhere.

The diagram below should, hopefully, make it clear and describes a full 4 stroke cycle.

If you know which cams you have I may have a diagram comparing them to the standards.

As Trevor says, any deviations from the standard timing will likely cause problems, kick-back, fire in the carb and general swearing and disillusionment.

cheers
Pete


email (option): petercomley@web.de

Re: 1948 big bore B33

This is getting more complicated than it needs to be...

The valve timing is virtually self explanatory as described in my last post...If any marks are missing off the crank pinion replace it with one that has the marks and any doubt will be removed...I think anyone can line up two marks...Entering a discussion on the theory of valve timing will only cause more confusion IMO and isn't required to carry out a very simple setting where everything is marked to make it so...

Regarding the ignition timing following the article in the technical section will a) explain how it works and b) tell you how to do it...Once 'a' is fully and properly understood 'b' should be relatively easily achieved, maybe not at the first attempt through lack of familiarity, but soon after I'd have thought...

The key thing with ignition timing is to fully understand what you are trying to achieve and the reasons for it...Random adjustments without understanding the theory and method are unlikely to produce the right result....Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

agreed Ian.

But this poster also posted on the Brit Bike forum and mentioned that the cams were not B33 standard but Goldie versions. I fitted Goldie cams that I had knocking around to my B31 and although these were stamped with the appropriate number there were no timing dots and dashes - maybe mine were defect in this respect- which meant I needed to time the cams with a degree disk and the appropriate info. I thought the additional info might come in useful if this was the case here, and avoid frustration if trying to time the cams using the info from Trevor's post.
I'd personally advise picking up a set of standard cams, dirt cheap to come by, and use them to be 100% sure that the cam timing is not an issue. Then look for any remaining problems.

in any case....good luck!

cheers
Pete

p.s there were also a few other deviations from standard mentioned on the other forum, such as modified conrod length which may have some relevance.

email (option): petercomley@web.de

Re: 1948 big bore B33

If genuine Goldie touring cams (the type mentioned in the original post) or any other genuine cams are being used, they should have the timing marks on them and they are set in the same way as standard ones... However, the individually numbered cams are not interchangeable between inlet and exhaust like the standard ones so must be fitted in the correct position....

After market cams with no marks would be another thing altogether...Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

Hi, and thanks for all your posts, The cams in question are goldie touring 2448, 2450, these were already fitted to the bike before strip down, and the bike ran well, unfortunately i didn't take a note of their alignment before removing them, i only wish i had!
I'm pretty sure i now have them aligned 'as standard' Yes, the engraved line used to align the inlet cam was missing from the pinion, but that wasn't a problem as i found a picture showing the settings and simply aligned the exhaust cam first (dot to dot) and counted the teeth counter clockwise to align the inlet.

Re: 1948 big bore B33

I found this...


Cam 65-2442 O.B.T.D.C 65º C.A.B.D.C. 85º Lift 0.442 in
" 65-2446 " " 63º " " 72º " 0.404 in
" 65-2448 " " 43º " " 73º " 0.380 in
" 65-2420 " " 25º " " 65º " 0.300 in
" 65-2444 " " 60º " " 85º " 0.422 in
Exhaust Valve Timing (with 0.018 valve clearance)
Cam 65-2446 O.B.B.D.C 80º C.A.T.D.C 55º Lift 0.404 in
" 65-2450 " " 70º " " 45º " 0.380 in
" 65-2452 " " 64º " " 34º " 0.370 in
" 65-2491 " " 95º " " 50º " 0.421 in
" 65-1891 " " 85º " " 60º " 0.423 in
" 65-2420 " " 65º " " 25º " 0.300 in

Standard cams data i have is.
inlet opens 25 BEFORE T.D.C , CLOSES 65 AFTER B.D.C
EX OPENS 65 BEFORE B.D.C , CLOSES 25 AFTER T.D.C

Re: 1948 big bore B33

Sorry , I was not trying to make things over complicated.
Either one of 2 things ( assuming it is not fuel ) is happening.
Either the spark is out of time or the cams are out of time
Now I use a timing disc for timing the mags & cams. And I copied these 40 years ago from the MotorCycle article "Timing by Degree".
These were marked out for each bike so the numbers were never needed again .
Because BSA cams run off the same pinion it is very easy to get the cams backwards.
Also because most time the engine with the timing cover on it is very easy to set the mag on the wrong stroke particularly remembering that when standing on the primary side the crank counter clockwise and all of the tuning information assumes you are on the timing side where the crank rotates clockwise.
Thus the quick and easy check is the skewer down the plug hole so you can correlate the position of the piston with the position of the valves.
I suppose I should have just said that rather than typing the longer approximate instruction which as Pete rightly mentioned was not accurate and corrected

And on the subject of Pete, where did you get that timing disc illustration from ?
I am still using ones I photocupied from the Motorcycle "Timing by Degree" article which are getting really grubby

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

Hi Trevor

I knocked up the cam charts myself on a wet evening some time ago. I have several for the BSA GS cams and some comparisons between various cam combinations. I found it easier to look at the diagrams than juggle the numbers in my head.

I think this one covers our friend's current situation.
valve overlap in yellow


Standard-vs-Touring-2448-2450

Re: 1948 big bore B33

Thanks guys, truly outstanding! I've never used a timing disc before, i will get my head around it and give it a go!

Re: 1948 big bore B33

Just to throw a spanner into the works, I've discovered the cams i have fitted are actually 2436 & 2438, which i understand are the earlier un-ramped version of the previously specified cams!
These pinions have 36 teeth, so i figure one tooth is 10 degree? I cant see that its possible to fine tune the valve timing as any alterations can only be made in increments of 10 degrees (1 tooth) or am i missing something?

Re: 1948 big bore B33

Actually it is 20 deg as the cam shafts turn at 1/2 crank speed

It took me a few minutes to understand why Pete's disc looked so clean & obvious till I realised it is a cam timing disc not a crank timing disc as it spans 720 not 360 .
Some times the brain is even duller than other times.

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

Now I have no experience of this so feel free to shoot me down…but…

Having a look at the cam info I have it appears that most have similar figures for when maximum lift occurs so that might be a starting point.

The standard cams are inlet and exhaust 70° BBDC and 70° ABDC whereas the majority of the GS cams seem to be 75° ABDC inlet and 77.5° ABDC exhaust, for the touring cams, (scrambles are a bit different for inlet). Maybe it would be possible to get close to these figures with the cams available? myB33 did say it was running with those cams before, in his original post on Brit Bike, so it must be possible.

yeah, my diagrams are not for timing the engine, don't try sticking it on the end of the crank, but just give me a clearer idea of how the various cams relate with open/close/overlap.

Re: 1948 big bore B33

Thanks again for the replies, i have a timing disc on order and will let you know how i get on with it.
Also picked up a projected electrode plug to see if it improves the spark,
Yes Pete C, the bike was previously running with these cams.
thanks

Re: 1948 big bore B33

Ok an update on the non starting issue, well I've spent hours on it and it still refuses to start!
I now have standard cams installed, using a dial gauge & timing degree wheel i found true TDC and confirmed that both valves open and close when they should & the tappet clearances are correct. I have ignition set at 11 mm BTDC full advance on compression stroke, I observe the inlet valve go down and return, continue forward until TDC both valves free push rods rotate, turn engine backwards and then forward stopping at 11 mm BTDC, with points just starting to open (correctly gapped at 12 thou) Whopping big spark evident when plug rested on cylinder head and kicked over, carb, Amal 932 stripped and cleaned several times, plug gets moist when engine is kicked over, tried petrol down the plug hole, damp start spray, going to try some fresh petrol next, but still refuses to start, cough, nothing...any ideas anyone? this thing has really got me stumped!

Re: 1948 big bore B33

I'm reluctant to add to this, as so many far more experienced folks have already added their considerable wisdom to this discussion.

Instead I'll recount what happened to me when I had a similar problem after replacing a head gasket on a B33. Frustrated and disgusted with the engine's inability to cough to life I decided to have a think. While doing that "thinking" I elected to change the oil to a winter blend as the autumn was definitely making itself felt. At the time everyone was advising me to use 20/50. So I did. Result? The cold engine spun just a shade faster and immediately sprang to life.

Allan

email (option): allanmatchless@yahoo.com

Re: 1948 big bore B33

And one from very left field.
A motorcycle shop contacted me because he was having problems with a customers B33.
It would work in the shop but a week latter in the customers home it was a no go.
He would bring it in the mechanic would clean out the carb double check everything the bike would start & run just fine.
The mechanic refitted the tank & filled the tank with fresh fuel.
Took the bike for a test run, then dropped it back to the customer.
Next weekend the customer could not start it.
THis went on for months till just for the heck of it he tipped out the petrol & put it into a known good engine.
That one would not start either.
What was happening was over the week the volatile elements in the local slop we call fuel was reacting with the tank liner resulting in fuel that would not ignite at room temperature.
A new tank was fitted & the bike has been running like a top for the past 11 years.

email (option): bsansw1@tpg.com.au

Re: 1948 big bore B33

['Instead I'll recount what happened to me when I had a similar problem after replacing a head gasket on a B33...']

Good point about the oil, a 'wet sumped' engine can also be a pig to get started due to oil drag on the crank...

Regarding the extract from your posting...The B33 shouldn't have a head gasket..The head is lapped to the barrel spigot like a valve. Not having a head gasket is one of the major plusses of the B33 I've always thought!...Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

Thanks all for the latest replies, fresh petrol is the next thing on my list, I did reseal my rusty petrol tank, but at moment the bike is hooked up to one of those small portable plastic tanks suspended above the bike,being purpose made for the task the plastic should be good...maybe? The oil grade is interesting, i'm using a mono grade sae 30, wet sumping is always a problem, i fitted a drain bolt to the sump and usually drain it before kicking over. I'm investing in a compression tester as i think that needs looking at as i think I've tried most things!

Re: 1948 big bore B33

You are right, of course, Ian. It was a long time ago and my memory is not always at its best when thinking of bikes I now no longer own. I had the B33's head off (for valves) and so I made the mistake of thinking there was a head gasket in the process.

Profuse apologies!

Allan

email (option): allanmatchless@yahoo.com

Re: 1948 big bore B33

No need to apologise...I frequently can't remember what I did yesterday, or what I have to do tomorrow....As for today, getting the day of the week right and remembering where I've put everything is the challenge...:laughing: ....Ian

email (option): ian@wright52.plus.com

Re: 1948 big bore B33

Hi, I've done a compression test, say no more the compression is down, what sort of reading would be considered healthy? i reckon about 130 ish?

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