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B33 short rod high comp piston #788518 10/29/19 6:41 am
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Dean44 Offline OP
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Hi all

Am new here. I have a few brit bikes and among them is a 1954/56 B33.It is a real bitsa and i had had it for about 15 years and my dad wants to start trying to get it together. The head has been put together with some bigger than standard valves and some flow test work. This was done about 10 years ago and I can't really remember the specifics. I do seem to remember the guy that did the work saying it should go good at about 9-1CR

My question is as i would like to go a bit higher than the standard 7.5-1 CR and i cant seem to find a B33 piston to do this. Has anyone fitted a goldstar rod and piston to a short rod B33? Is it a straight swap? is the deck height right?

As far as i can tell the "throw" of the GS and the B33 is the same so should go straight in.

The bike was completely in bits when i got it so i have no references.

Alternately is there another piston that will fit without too much work to give a higher CR

Thanks in advance
D

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Re: B33 short rod high comp piston [Re: Dean44] #788544 10/29/19 4:26 pm
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Gordo in Comox Online Content
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Dean: Looking at the refs I have the B33 went to a 6.875" rod in 1953. The GS short rod is 6.468". That is quite a difference. To really know the answer you would need to also compare the height of the piston deck above the wrist pin. I do not know how the barrel heights compare. Measuring a DBD piston I get 29/32" from the top of the pin to the top of the deck ( not dome ).

Have you tried these guys?


https://www.feked.com/gandini-gpm-piston-bsa-b33-m33-short-con-rod-models-circa-1952-60.html
Gordo

Last edited by Gordo in Comox; 10/29/19 4:37 pm. Reason: added link

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Re: B33 short rod high comp piston [Re: Dean44] #788595 10/30/19 3:44 am
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Dean44 Offline OP
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Hi Gordo

I have a 6.875" rod that was in the box of bits and know that the GS rod is shorter. The question is, is the difference in the rod piston combo or as you have said, is it in the barrel height also? The problem is I don't have any B33 piston to compare.

Does anyone have a short rod B33 piston that they could measure the pin to top of deck height so i can compare the measurement that Gordo has supplied?? This will tell me if it is all in the rod and piston.

Was thinking someone must have tried this before I go and buy a GS rod and piston.

I did have a look at Feked but the piston they list is (as per the link) is quite low comp; 7.5-1.

Anyway thanks for you input.

Cheers
D

Re: B33 short rod high comp piston [Re: Dean44] #788596 10/30/19 5:27 am
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Gordo in Comox Online Content
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Here is an old thread llnk with some info. There is a DBD cylinder height given and other B33 data

http://britbike.com/forums/ubbthreads.php?ubb=showflat&Number=627962

Gordo


The roadside repairs make for the best post ride stories.

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