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Vassal

B&S Crankshaft compatability

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Vassal
Looking in the Illustrated Parts List for various Briggs engines, I see that it is common for several crankshaft PN's to be listed for a given series (326400, 243400 etc). I understand that there is good reason for this as there may be several output variation for PTO's clutches etc., yet this brings me to ponder a few things. My example- 326431-0190-01 7501231 In the most basic format as it applies in my 7016H (no pto clutch etc), is it considered absolutely mission critical to have the EXACT crankshaft for the engine's "type number" ? Here's why I ask: For my type # 0190, the crankshaft is still available new, however it is far more costly than other new PN's I have found for different 'type' numbers within the series. Would the others work? Also, does anyone know if the cast iron 326400, 243400 engines as they apply in our tractors are balanced internally, externally (flywheel) or a combination of both? Finally, do any of you guys just 'wing it' and slam any series compatible crankshafts into these engines (given output shaft compatibility)? I ask because I wish to learn these things, not because I'm a smart alek. sm06wait, who said that?sm06

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Chris727
The 30000 and larger (12 through 16) are synchrobalanced. The 243431 (10hp) is not synchrobalanced, and is quite a bit different from the 30000 and larger engines. There are many parts that are common between the 12 through 16's but not as much is common between the 10hp and the 30000 and larger engines. Some of the engines had 2 sets of balancers, these may have different cranks from the ones with a balancer only on one side.

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Vassal
Thanks Chris, I think you almost answered my main question and you answered another that I was pondering too. What I'm most concerned with is using crankshafts for different engines in the same model series (326400). In other words, without having both crankshafts on the bench, is there a way to tell if one 326400 crank will work in another 326400 engine with a different 'type' number. I'm thinking this might require a crystal ball thoughXX(

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Chris727
I think I might have seen a 326400 with double balancers at some point (most 16's only have it under the flywheel), I believe if it has double balancers the crank will be different but I wouldn't know for sure without looking up numbers.

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HubbardRA
You will need a crankshaft for the same size engine. A 16 Hp engine has a larger piston than a 12 Hp engine. Because of this the counterbalance weight on the crankshaft must be heavier to offset the piston and connecting rod weight. The crankshafts will interchange, but if you put a 12 Hp crank in a 16 Hp engine it will be significantly out of balance. Don't get this confused with the rotating synchrobalance weights. The rotating weights are there to remove the secondary harmonic vibrations. The primary vibration is still counterracted by the weight on the crankshaft. If you search in some of the tractor pulling forums you can dig up information about re-balancing a crankshaft for use in a different engine than it was designed for. As an example: A 14 Hp and a 16 Hp Kohler K series engine both have the same balance and use the exact same crank. Even though a 12 Hp crank starts out the same and will physically interchange with the 14 and 16 engines, the 12 Hp crank has had more of the counterbalance ground off at the factory because the piston and rod assembly that is used in a 12 Hp is much lighter than the one on the other engines and requires less counterbalance weight to offset it's rotating mass. To use a 12 Hp Kohler crank in a 14 or 16 Hp engine, it is necessary to weld weight back on to the counterbalance to balance the crank for the heavier crank and rod assemble of the larger engine. What I am trying to say is that the cranks can be assembled in the other engines, but will throw the engine entirely out of balance. It is much more than just a problem of physically fitting the other crank into the engine. I looked into this because I wanted to build up a 14 Hp Kohler engine but did not have the crank, so I wanted to use one out of a 12 that I did have. I never did go through the re-balancing process because I found a running 14 Hp engine for a reasonable price and used that.

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Vassal
All this makes perfect sense. It's amazing how much I've learned here in such a short period of time! Thanks guysdOd I was thinking the various crankshafts were for different configurations unrelated to the the balance issues. But now I understand that these engines are much like any other that require reciprocating balance as well as harmonic balance. One other thing - Do you think the synchrobalance for these engines was primarily developed to please customers (smoother engine) or do you think it (also?) has a significant affect on long-term durability? Thanks again!

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HubbardRA
Synchrobalance(harmonic balance) was developed to smooth out the engines for tractor operation. In all-out pulling competitions where the HP is tripled and the RPM are at 7000+, they always remove the synchrobalance weights, but are very picky about good dynamic balance.

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