Mercruiser coupling tolerance

Wonder if anyone can advise on my install.

I have converted a couple of engines to connect to my alpha legs. Everything has gone smoothly, the only issue i have is I have done my absolute best to centre the coupler on the flywheel. I have two as it is a twin drive. One flywheel the coupling is 0.4mm out of centre, the other is 0.8mm out of centre. Now I know that this is such a tiny amount but I do like to check as I cant find any information on weather there is an acceptable tolerance.
Its the typical coupler with the spline centre within a rubber bushing. Any advice would be great regarding this small discrepancy.

 

Hi Vidi79, both of those numbers are not good. It's not a small discrepancy. You should aim for less than 0.1 mm, or 0.004 inch; however 0.05 mm, or 0.001 inch would be much better. Use a dial indicator to help centralise the coupler. Consider the vibrations and strain on everything at high rpm from something wobbling about forcefully for hundreds, or even just dozens of hours. It could speed up bearing failure, seal wear, metal fatigue, and cause vibrations in the hull.

 

Thanks for this.
I understand the importance and a you sy what I call small is actual pretty big and so yes I will decentralised it.
I have the gauges etc to do this so that isn't a problem.
The best way for me to centralise is is to slightly widen my bolt holes on the coupler, tap it into position and the tighten up.
My existing holes are really snug, will enlarging them cause a risk of it slipping in use or do you think well tightened with spring washers will hold it firmly in place?

 

What kind of engines ?

 

Vw pd tdi

 

The friction between the flywheels and coupling flanges when bolted up tight is what holds it in place, not the bolts themselves, so minimally enlarge your coupling flange holes just enough to tap the couplings across into concentric position. Also use some thread locker / nut locker compound once it is well aligned, so not relying on just spring washers. If your couplings are clean and in good round condition, and you have a dial indicator, you should be able to get them much truer. Aim for as good as you can get, and it will save future repair work. The hard part will be slowly turning your engines over by hand to find centre with the dial indicator. Don't run engines with the indicator running on the coupling, or you will destroy it. I'm not familiar with those engines, but it may be easier if you could disconnect the injection common rails, and remove the injectors carefully, so you're not fighting against engine compression when turning over; unless it has de-compression valve lifters. In a petrol engine you would simply remove the spark plugs. Seems like you should be able to do a good job of alignment, so good luck, and post some pictures of your conversions.

 

BKC , ARL ?