Balancing 4 Cylinder Engines

Engine building advice and Q&A with Jeff!

Balancing 4 Cylinder Engines

Postby FRP » Tue Jun 11, 2013 8:55 pm

Hey guys sorry it has taken this long for me to get back here - just really busy in the shop and at home.

Regarding inline engines with an even number of cylinders:

Most of you know that 4's and 6's inline, are self compensating with regard to rotating and reciprocating weight. But this assumes that all these weights are equal, so you still need to have the piston and rod weights equalized down to about a gram. This is done in the same manner as described in the 5 cylinder article.

More importantly the crank needs to be put in the balancer (without bob weights) and checked for zero balance. This is because, frankly, sometimes the factory just does not get them very close. This step just assures that the counter weights and rod throws are in equilibrium and you have a zero balance foundation to carry the rest of the rotating assembly. The lack of real consistency here is why some engines "just seem to run smoother" (or rougher) than engines of the identical type and model year.

If the engine is going to be used hard and you want maximum smoothness and durability you just have to go through these steps so you know what you have. Remember - "Test - Not Guess"!

Cheers, Jeff @ FRP (I promise to get the crank damper post done soon)
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Re: Balancing 4 Cylinder Engines

Postby speeding-g60 » Tue Jun 11, 2013 10:08 pm

mine are always balanced to within one gram overall. including the rotating assembly with the FW/PP but not the 3 discs as they are dynamic parts of the load not static. crank zero'd, all compnents weighed and ground big end and small end, to be matched.

also, not supposed to balance with a Fluidamper type dampener at all, either.

i think i push my 4 cylinder stuff pretty hard....

one last thing; when mine is done, the PP/clutch cover is marked to the FW so it ALWAYS GOES BACK IN THE SAME SPOT.
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Re: Balancing 4 Cylinder Engines

Postby loxxrider » Wed Jun 12, 2013 8:29 pm

Thanks Jeff, good info. Looking forward to some crank damper discussion. Hopefully we can get to a solution on mine soon!

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Re: Balancing 4 Cylinder Engines

Postby Lord_Verminaard » Tue Jun 18, 2013 10:49 am

Thanks so much!

So what that means for us non-hardcore race types that want to build a stout street engine, if we balance rods/pistons/etc within one gram of each other, and have the crank zero balanced as well, that should be good enough? Sounds easy enough to me! :)

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