Big bore BSA B33

Tbh , how to end up with a favourable compression ratio eludes me, I have it in my mind, stroke, bore and finalising with compression gives you the desired ratio??
Some advise here would be very helpful...!
One reason I prefere to adhere to a lower compression is that I want to fit an electric starter as my knee isn't all that strong, thats another reason I thought it best to go with a short rod in the first place, a shorter kick to complete one engine cycle?
Cheers
Catweasle
You said you already had a shovelhead piston in it , if you haven't got the gear , the compression tester reading will give you an idea of the ratio there are charts on the net , as I said my 170 equates to approx 8.5:1 . Let us know how you get on with the springs etc .
 
Tbh , how to end up with a favourable compression ratio eludes me, I have it in my mind, stroke, bore and finalising with compression gives you the desired ratio??
Some advise here would be very helpful...!
One reason I prefere to adhere to a lower compression is that I want to fit an electric starter as my knee isn't all that strong, thats another reason I thought it best to go with a short rod in the first place, a shorter kick to complete one engine cycle?
Cheers
Catweasle

You said you already had a shovelhead piston in it , if you haven't got the gear , the compression tester reading will give you an idea of the ratio there are charts on the net , as I said my 170 equates to approx 8.5:1 . Let us know how you get on with the springs etc .
Thanks for the advise, much appreciated. I've a friend who's offered me to delve through a huge stash of springs he has collected over the decades, I might be lucky to find something there, otherwise I could use the terry spring specs as a bench line and have custom springs made to order.
Cheers Catweasle
 
Hi guys, anyone got specs for the following goldie cams?

65- 2436 ex
65- 2438 in

It would be of immense value!

Catweasle
 
Have you got any books , I bought a couple of bsa books , I haven't got time at the moment but will look later .
Big bore BSA B33
 
My research suggests the cams are 1949 goldstar 500 🤔I also have another set of cams which I assumed were standard as there's very little in the way of stamping on them, turns out I was wrong, I measured the lobs and they have an even greater lift 🫣

Likewise I've also invested in some goldstar reading material!

Im still scratching my head with the coil binding issue, so I've ordered an new set of the standard terry springs, so least I have a know benchmark to work from 🤔
 
I said the springs were tricky 😗, it's because of the fixed rocker pivot , so you can't make the valves longer , the easiest is less coils otherwise , if you have a junk head cut it through the center of the valve spring seat , so you know how much meat there is before you go into the port , you could then machine some material from the spring seat . To gain coil clearance , those terrys 345 springs only have about 60lb , well on mine any way, my keepers might be higher as I had drama with the rocker hitting the side of the retainer
 
I said the springs were tricky 😗, it's because of the fixed rocker pivot , so you can't make the valves longer , the easiest is less coils otherwise , if you have a junk head cut it through the center of the valve spring seat , so you know how much meat there is before you go into the port , you could then machine some material from the spring seat . To gain coil clearance , those terrys 345 springs only have about 60lb , well on mine any way, my keepers might be higher as I had drama with the rocker hitting the side of the retainer
Tricky, you could say that! I was tempted to remove some material from the head as you suggested, maybe as a last result! As for measuring I was just going to use a dial gauge for max lift and probe between the coils with a feeler gauge, cutting up the head is for later retribution should it blows up 🫣😁
 
I think the answer is changing the springs , maybe those R100 springs could be worth a look , or find some specs , your average spring maker doesn't make valve springs , I think they are chrome vanadium , if you have additional valve lift , that will be an extra problem as well .
 
I think the answer is changing the springs , maybe those R100 springs could be worth a look , or find some specs , your average spring maker doesn't make valve springs , I think they are chrome vanadium , if you have additional valve lift , that will be an extra problem as well .
Thanks for the help, I'll be sure to post an update when I've made some progress 👍
 
I've been taking some measurements today to cure the valve binding issue.
I wanted a measurement of exhaust valve lift with the goldie cam fitted, but I took the reading at the push rod lifter, it measured 8.28mm of lift, is this a true way of taking the measurement ? does the valve tappet make any difference to that reading? I can't quite get my head around it tbh 🤔
 
I've been taking some measurements today to cure the valve binding issue.
I wanted a measurement of exhaust valve lift with the goldie cam fitted, but I took the reading at the push rod lifter, it measured 8.28mm of lift, is this a true way of taking the measurement ? does the valve tappet make any difference to that reading? I can't quite get my head around it tbh 🤔
Hi Catweasle, no it won't unless the rocker ratio it 1:1 , if you have a dial gauge put it on the side of the retainer, set your tappet first , you can easily calculate the rocker ratio from your two measurements .cheers
 
Thanks for the reply, I'll give that a go.
On another subject any idea what size thread is used for the cylinder head bolts?
 
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Good news the coil binding issue is finally solved!
I finally achieved it by lapping the valve seat in, removing some material from the retainers and then the spring it self.
Thanks everyone for their input 👍
So onward to the next problem, the head bolts😁
 
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