DOHC Seca/Maxim Engine Differences

[OopsAboutThat]

Hey all!

I've recently started an engine rebuild here and I have a Seca engine as well as a Maxim engine. My plan is to use the best bits out of both engines. I've checked part numbers and it seems that the crankcase, head, cylinder, valves, camshafts and most other internals are all matching between the two engines. The crankshaft that was in the seca is pretty nasty but I want to use the cases from it. While comparing, I noticed that the crankshaft is actually different between engines, while the balancer shaft remains the same. Here are some pics:

The one on the right is out of the Maxim, and as you can probably see, it's got a lot more meat on it. I was wondering why this is, and if I can use it in the Seca cases with the matching Maxim balancer shaft and Seca 6 speed. If so, would there be any major affect on the engine? So far our theory is that the heavier crankshaft yields more torque in lower gears/rpms for the Maxim 5 speed. Since the crankcases have matching part numbers, swapping them out should be fine, so long as I use the correct bearing shells, right? Thanks for any input or suggestions you may have! If anyone else knows of any differences between the two engines feel free to chime in.

 

[Jeff0133]

I've used two engines also, a Maxim and a Seca and made a 6 speed rebuild... Everything fits just fine.

 

[OopsAboutThat]

Awesome. I figured it would, just wanted to know anyone else had any experience with mixing up the crankshafts. Thanks!

 

[Jeff0133]

I would think that the extra weight would cause more inertia and rob you of hp...I might be wrong on this just throwing it out there.

 

[trife86]

Would prob rob of some HP but on other hand, being rotational mass is heavier might be easier to maintain speeds?

 

[16VGTIDave]

Extra mass will cause extra inertia. With rotating components, this will result in slower acceleration, slower deceleration, and smoother running. And generally speaking, increased longevity. On a street or off-road vehicle this is a good thing, on a track race vehicle (that only has to last a couple hours) parts are made as light as possible for maximum acceleration. To the point that they now are having to use traction control to keep race vehicles manageable.

I've driven cars with lightened flywheels on the street. Strongly not recommended! Very difficult to get the car moving without revving the engine and slipping the clutch, or stalling...

 

[OopsAboutThat]

Thanks for the input guys! Good thing I'm not building a performance machine here. Think I'll go ahead and use the heavier flywheel, seeing as it's in much better condition. Always really neat to hear about what goes into engine design and how much "little" things can change the overall running of a machine.