Bis con rods.

[1973/126]

 So here is a question for the bis boys.
 Is there anyone out there with a bis engine in bits who could measure the length of the con rods for me?
 This measurement would do.
 

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[DEYAN IYI]

The aircooled ones are the same.

[1973/126]

 Thanks Deyan. I thought you might be the man to answer this.
 

[DEYAN IYI]

You welcome

The stroke is 70mm in both engines. The Bis cylinder is 6mm shorter. If you want to put Bis pistons in aircooled cylinders with standard rods, the lower end must be skimed 6mm, that's about one cooling gill, before building the proper jackets in. Or you can find 118+6mm rods, that wouldn't be easy. Also, not a good idea to use Bis pistons over original aircooled crankshaft.

What's the problem you are trying to solve (if it's not a state secret)!?  

[1973/126]

 That was exactly the idea. using bis pistons which I already have and use a 76mm stroke crank, or longer con rods. I just wasn`t sure if the bis con rods were longer, or the cylinders shorter.
 I probably gonna give it a go with the con rods as I found some for a reasonable price. Those 76 cranks are a bit expensive and I`m trying to do this on a "sensible" budget.

 Why do you think the bis pistons wouldn`t work well in the A/C engine? I heard of people using these before.

[DEYAN IYI]

They will work, but you can't be sure if the standard crankshaft will survive. That's what Polish guys say. If you stick to 70mm stroke, go for Bis's one - harder and better balanced in high revs. Some people have worry about the pulley (in Bis is bigger and does not fit in aircooled), but anyway the moving group will be dynamically balanced, so it will be OK.

76mm crank sounds pretty abarthic and torquey, but...

PS - eyesore... original crank after hard tuning also original conrod (if I remember well, the block is 500).

[1973/126]

 Deyan I only just spotted these pictures. That looks nasty.
 I think Smallcox is still running a standard crank and seems to manage. I know he destroyed a brand new crank though on higher boost.
 Is there any other alternative with the crank? There must be a company who makes some stronger ones, surely.
 
 

[DEYAN IYI]

The only cheap alternative is Bis or CC700 crank. Here and there are some sport cranks, even on 3 main bearings.

Matushka has also this one with 75mm stroke.

Here this for example.

[Pete126]

The only cheap alternative is Bis or CC700 crank. Here and there are some sport cranks, even on 3 main bearings.

Matushka has also this one with 75mm stroke.

Here this for example.

Ooh Nice

[1973/126]

 Hey Dyan thanks for that. I`ve seen them cranks and that what started the whole idea about the bis pistons. The 126Fan guys used to do a 77mm stroke one, but they run out of stock very quickly. I know they even sent some to Italy as they are nearly 1000 Euros there.
 That 75mm one is still very tempting, but maybe for another project.
 
 On the other hand I received my 6mm longer con rods to go with the bis pistons and they are very nice. Both way exactly the same to the gram and are even lighter than the standard ones. However there is no oil ways in them. I checked all the other aftermarket con rods and they all seem to be the same. Has anyone got any experience with these?
 Anyway here are some pics.
 
 

 

[DEYAN IYI]

Mmmm, nice things  About the oil holes, in the big end they seem to be just kind of reservoirs (in our case, does not spray to the cylinder wall or leads oil to the small end). The small end looks like drilled on top!?