Ok, I just got a huge swap finished, probably the only of its kind in the world. I don't recommend it,

So I have a Mitsubishi 4M40 4cyl Diesel of about 96' vintage. The engine has been fully rebuilt, new liners, new head, well new everything.
Had the injection pump professionally rebuilt as well as the injectors with all new pintle's, so its been gone through quite extensively....Problem is, I think this could be bad, real bad.
We had to mate it to a tiny little Renault front wheel drive transaxle, in the process of doing this the flywheel was extensively cut down and I mean cut down. I unfortunately did not weight it after machining.
The machinist did give me an ominous warning telling me he would be surprised if he engine would even run with so much weight cut off.

Injection pump timing could be a possible issue but essentially it will not idle. It fires right up, it revs faster then most gas engines but when you try to idle it just starts vibrating the chassis at anything below 1500rpm and if you let your foot off
the throttle it just dies immediately. Setting aside the potential for the pump timing to be out, which is possible but the fact it fires right up and revs up clean and smooth with no smoke tells me its probably at least well within the ball park.

The original flywheel was 25kg/55lbs, probably cut close to 15-20lbs off the flywheel. It was professionally balanced so its not a case of it being out of balance, and again, once you get above 1500 its smooth and super revvy.
And yes, I know the machining is a little rough, but its the local machine shops I am forced to deal with.

So at the end of the day, is it possible that removing so much mass from the flywheel could prevent the engine from idling due to the loss of rotational mass being able to carry angular velocity between power pulses?


Original flywheel backside

Original Pizza Wheel front side

Yikes, thats alot of material removed

Here it is cut down to the size of the La Petite Renault flywheel.

 

So upon further research it looks like the original flywheel may have been as heavy as 40kg which would be 88lbs.
Like I said I never measured it, I remember it being quite heavy but sadly I don't have a specific weight. I am
going to measure the original Renault flywheel today and that will tell me approximately how much the
current flywheel weighs since I had the Mitsu flywheel cut down to match the dimensions of the Renault.

This should give me an approximation of how much weight was removed, either way the excess low speed vibration and engine stall would all be symptoms of an excessively lightweight flywheel on a diesel application.

I think this project may require a redesign, I told this guy not to go down this road but here we at the cliffs edge.

 

So quick update, turns out I did in fact get the injection pump off a tooth, once I got this corrected the engine does in fact idle stable.
Still alot of vibration but I also have 75D poly mounts which in hindsight was a bad choice for a diesel install.
I have some stout HD Rubber mounts in the shop awaiting to be installed and will report back.
Not sure how I convinced myself that the flywheel was an issue, I guess I didn't want to believe I had the pump in wrong.

Also have a charge air temp, boost and egt gauge package on the way.

C/Ya

 

Any more update?