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Crank shaft counterweight drillings

F

Frey

Tuned and Synch'ed
Joined
Oct 8, 2015
Messages
44
Location
Happy Valley
I obtained a 1979 MG V1000 G5 last fall. It had been in a garage for the past 25 years after about 30K miles in its first 13 years. Single-owner bike (it belonged to a guy who was turning 80) and relatively unmolested. It seemed to have good bones (although being completely caked with crud) and a be a good candidate for restoration. I have since had the frame powder coated, gotten some new parts and started putting the jigsaw puzzle back together.

While the engine was out, I had the heads and valves ground. The bores actually looked great, so I decided to leave the bottom end alone. Yesterday, I rolled the engine onto some blocks (alternator side down) so I could easily attach the sump cover. Things inside looked pretty good although I did notice that I wasn't the first to be inside. The (substantial) crank shaft counterweights had been drilled. Holes are radial to the crank axis. More interestingly, one of the two weights has two holes, the other 5 (if I remember correctly). I'm not aware that either of the pistons was ever replaced and I'm assuming they're stock.

Couple questions:

1) WTF?

2) Even assuming (which I don't) that the removal of material was to balance piston mass, what would explain the significant difference in number of holes?

3) Will the difference in weight of the counterweights have a substantial detrimental affect on the crankshaft bearings?

4) I wonder if the holes (being on the end of counterweight instead of inside the lip and parallel to the axis of the crankshaft) scoop oil from the sump and contribute to blow back into the filter box? I don't remember the filter itself being oily, but it might help explain why the thing was so mucky. If there's something to that theory, it might be remedied by the deeper sump cover with the external filter mod.

Appreciate any advice and anecdotes on this issue. For the moment, I'll halt the reconstruction. I sure would like to not have to remove the engine and tear it apart.

Cheers,

Frey
 
the density of the crankshaft steel is not uniform , so although the crankshaft is machined symmetrically when spun at speed these slight differences are magnified.
with your crank one end was significantly out.

the crank will not touch the oil to spread it around normally .....unless you've over filled it

I do dynamic balancing with my job (winch Impellors) for our targets we tow for the navy to practice on.
 
Thanks, Android. So, I speculate that your advice would be to get 'er running and if it doesn't have too much vibration, let it be?
 
wait. that series had bad clutch hub spines. Too soft! my 81 G5 after about 10000 miles would all of a sudden jump forward while sitting in first at a stop light. replace them while apart. maybe a real old timer will chime in here.
 
Thanks for that advice, vagrant.

Update: I talked to the original owner today to see if he could shed any light on the situation. He said that in the first year he had to take the bike in for warranty service and they had the whole engine apart. He couldn't remember exactly what the problem was. We can forgive him; it would have been 35 years ago. It was put back together and ran fine until he stored it a dozen years and 25-30K miles later. Vibration wasn't a problem. That's the only time the bottom end of the engine (and probably the top, as well) was ever apart. Assuming those facts, I'm tempted to leave it alone and see how things go and hope that the counterweight driller had some voodoo. I can always pull the engine again if I need to.
 
Didn't think to take a picture of the crankshaft while I had 'er open (doh!), but thought y'all would like to see what I meant when I said the bike was "caked with crud". A good 3/16 of an inch in places!
 
Vagrant is correct that that era bike had a poorly treated clutch hub. At this stage I recommend updating to the the 4mm spline hub and plates. Also just because of age, and new set of clutch springs wouldn't hurt either. Ir does help to have the special tools to remove the clutch hub and align the clutch plates for installation.
 
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