Hi:

I am new to the forum and here with a very challenging question. I have a 318 Chrysler marine in my 24' cruiser that went belly up a few years back. I recently located a 360 Chrysler marine engine complete ... well mostly complete - the wiring harness was junk. Switched the wiring harness before I pulled the old engine and just as I finished I noticed the 360 only had one wire to starter. Took the 318 starter out but it wouldn't fit in 360. Oh, oh. Then I checked the bell housing and discovered the bolt up pattern through the hull was different. Pulled off bell housing and same flywheel bolt pattern ... but obviously different size flywheel. Then I went on line and discovered the internal/external balancing issue. Okay, I found a blueprint for balancing a 318 internal flywheel to bolt on external 360. Fine. Or so I thought. Counted the teeth and the 318 only has 122 while 360 has 160 which is, as I understand it, unique to marine engine. The blueprint is for drilling out a 140 tooth flywheel. The 122 tooth for 318 is 12.3" not the ten incher for slant sixes. I presume 12.3" was used in 273 vehicle engines? My problem is I must retain the 122 tooth bell housing to mate with my 270 Penta outdrive. Both the flywheel and bell housing will bolt right up to the 360 but I need to find some way to get that small flywheel balanced to the 360 engine. I am desperate. Any assistance would be greatly appreciated.

Welcome here! I'm wondering if your shop could duplicate the balance of the 360 wheel over to the 318 one (I'm a 904 guy) & I did work on a 318 outboard speedboat once & it was a strange reverse rotation beast (that threw us for awhile).

the pattern is to locate where to remove metal to balance to 360 specs. It isn't flywheel specific, it is only engine specific.

How's your math! A balancer told me that trigonometry is needed to find the locations with the pic Supercuda posted. He also said that you can use smaller drill bits, that you're just wanting to remove the same amt of material but then there was the drill point angle difference so I just took it in & let them do it.

doesnt someone make a offset plate that bolts between the crank and standard flywheel that provides the correct imbalance to make the 360 balance correctly????

Quick Time RM531 balance plate. I used one on my 360 with a 318 flywheel and it balanced just fine. Bolts between the crankshaft and flywheel. They are about $30.00 from Summit.

Thanks. If the balance plate works, that would be the quickest fix (and cheapest!).

As far as I know this is a right hand rotation motor. Guess I should check the engine tag to be sure! Left hand rotation are more rare, usually found tandem with right hand rotation motor in twin inboard engine boats. Edit: My 360 is from an inboard/outboard and the prop rotation can be changed in Volvo/Chrysler outdrives so I'm pretty sure my engine is right hand rotation same as vehicles.

How do I know if this marine engine has a cast crank or forged crank? Does it make a difference for balancing the flywheel?

All 318's are internally balanced, cast or forged, so no difference in balancing the flywheel.

All 360's are cast, so no difference in balancing the flywheel.

This does not work out of the box. It needs to be balanced with the rotating assembly.

Supercuda: I am curious why the adaptor plate would need to be balanced with the rotating assembly. Like the flywheel, the balance plate only bolts on one way. Presumably it would balance as well as the blueprint drill pattern method which is also oriented to the crank's specific bolt pattern. Probably not super fine balance that one might desire for racing at high speeds but would the 318 flywheel with adaptor plate be any more imbalanced on a 360 engine than say a factory original 360 flywheel? Is each factory flywheel individually balanced to the engine it's mated to? Apparently not since, as I understand it, replacement 360 externally balanced flywheels can be purchased aftermarket "ready to install" without being re-balanced to the specific engine they're bolted to.

Because it is not balanced for any engine. Look at the application listing for it. Every Mopar engine that needs external balance is listed. There are are least four different imbalances I can think of that this plate claims to handle.

360 all 19.79 in-oz
340 cast crank 4.22 in-oz
400 all (includes 440 and 383 cast crank)12.9 in-oz
440 with heavy rods 6.5 in-oz


all have different imbalance weight requirements. What this plate does is take the place of the flywheel or torque converter as far as balancing goes. You bolt this thing to the rotation assembly and use it to neutral balance the assembly. then you can use any neutral balance torque converter or flywheel.

I'm a bit confused. You say: "You bolt this thing to the rotation assembly and use it to neutral balance the assembly. then you can use any neutral balance torque converter or flywheel." That seems to be exactly what I want. I need something that will balance the 360's engine ("rotation assembly") to eliminate vibration if its externally balanced factory flywheel is changed to zero balanced 318 flywheel. But you're saying the counterweight of this plate is not specific to what's needed for 360?

Edit: I see. The QuickTime product applications menu indicates the adaptor plate is not specific to 360 but applies to multiple V-8 engines Chrysler made from 1975-78 including, curiously, the 318 which I thought were all internally balanced.

So I'm better off having a machinist drill the 318 flywheel per the blueprint above? Or can the machinist tune the adaptor to meet the specifications you list? Guess I better cancel that order.

Take the balancer, crank and flywheel and have the machine shop balance it as a rotating assy.

I don't have the engine torn down and was really hoping to avoid that. Guess I could gauge the bearings while I have it apart but I'm sure it's not necessary. That engine had seen some use (owner claimed less than 100 hours) and was dirty but NOT oily. Very clean in that regard so I'm pretty sure it's tight. Lots of compression.

So drilling the 318 flywheel per the blueprint would not be a fix in itself either?

Why wouldn't drilling the 318 flywheel to the 360 drawing work? If you start with something that is neutral balance it shouldn't matter what the diameter is. All you are looking for is a certain amount of unbalance and the drawing gives you that.

that balance plate is designed with more imbalance than needed so your machinist can trim it to balance the rotating assembly as applicable to your specific setup. As it, it's not a bolt on. Not sure how to make it more clear.

The 318 is internally balanced, which make you wonder what Quick Time is thinking, or not thinking. there are no instructions and frankly the website is poorly, very poorly, written.

What your machinist can do is best asked of the machinist. But it should not be an issue for them to use the given prints and drill to match. No trig needed.

It stands to reason since the 360 takes the most amount to balance, then you would only have to trim it for the engines that use less weight to balance them. I installed mine as is, to my crank and then bolted on my 318 flywheel. No vibrations whatsoever.

And that is why I work on my own stuff.

Then I know it's done right.