butre
Well-Known Member
it's a blind hole, you would have to drill to the depth of the tip and then finish it with a bottoming drill
Too much vibration.
- Thread starter Eddiesilverbullet
- Start date
FurryOnTheInside
In Memoriam
I don't think it matters that the hole isn't flat bottomed.
The beauty of drilling from the outside edge is the ease of a trial and error method without the need for a full teardown.
I expect you can feel where the vibration is at its minimum and starts to come back again.
So we should be able to just drill conservatively at first, using Jaguar's calculator as a guide to drill bit diameter, and make the holes slightly shallower than the width of the crank flywheel.. Test.. Deepen.. Test.. Deepen.. Test..
Without the risk of going too far.
(Hopefully)
(Do tell me if I'm wrong, please)
The beauty of drilling from the outside edge is the ease of a trial and error method without the need for a full teardown.
I expect you can feel where the vibration is at its minimum and starts to come back again.
So we should be able to just drill conservatively at first, using Jaguar's calculator as a guide to drill bit diameter, and make the holes slightly shallower than the width of the crank flywheel.. Test.. Deepen.. Test.. Deepen.. Test..
Without the risk of going too far.
(Hopefully)
(Do tell me if I'm wrong, please)
D
Deleted member 12676
Guest
exactly. if your crank or crank pin is different than mine then the size hole may need to be different. Use the area calculator I linked to when determining which drill bit size to use. If you want to use a bit 75% the area of a 10mm drill bit then you'll see it won't be a 7.5mm bit.
butre
Well-Known Member
it doesn't matter that the hole isn't flat bottomed, it's just easier to calculate the weight of a cylinder than a cylinder with a conical tip, especially if that conical tip is concave or convex, or even worse stepped
FurryOnTheInside
In Memoriam
There's no need to calculate the mass removed. Jaguar's calculator gives you a guide but then you can test
__ because every engine is different, and the balancing is RPM specific, and you can make the hole deeper without tearing down the whole engine __
so if you want to balance for 6000 rpm then you can drill using the recommended bit size for 6000 (and your upper assembly weight) and make a shallow hole, test and see where in the rpm range the vibration is least, and where it starts to come back. Then just make the hole a tiny bit deeper and retest and repeat until you are satisfied. It should be a lot easier than the sideways hole and require fewer bits, I reckon.
D
Deleted member 12676
Guest
I just watched a video showing how out of round a crank wheel can be for one of these engines.
The variation of 12 thousands he shows in the video can equate to 8% of the counter balance which is a big amount. Where the high point is becomes very important. If it is close to the crank pin or on the opposite side (180 degrees off) then that can be compensated for with the counter balance holes. If not then it needs to be taken to the machine shop for them to lathe off the excess. With the top end and the primary gear off then you can put your finger on the case and let your fingernail rest on the crank wheel and then turn it. If you feel a high spot that is close to 90 degrees before or after TDC then you should take the crank out and take it to the shop.
The variation of 12 thousands he shows in the video can equate to 8% of the counter balance which is a big amount. Where the high point is becomes very important. If it is close to the crank pin or on the opposite side (180 degrees off) then that can be compensated for with the counter balance holes. If not then it needs to be taken to the machine shop for them to lathe off the excess. With the top end and the primary gear off then you can put your finger on the case and let your fingernail rest on the crank wheel and then turn it. If you feel a high spot that is close to 90 degrees before or after TDC then you should take the crank out and take it to the shop.
butre
Well-Known Member
I've seen even worse than 12 thou
gary55
Well-Known Member
This really is great data. I would like to add for those who are going to try this. It will help when flushing the case, to remove the magneto magnet. It transfers magnetism into the crank, mostly the wheel closest to it, and makes cleaning a pain.
45u
Active Member
I am getting ready to check the true on the cranks I have all new. To start with I will check the true together as I also want to check stock port timing on both short and long rod cranks with proper top end. Have other things I will be checking. Thanks all for the good input.
Last edited:
Wolfshoes
Member
My Landrider bike with the 66 Skyhawk China Girl resting on the frame like a V block has significant vibration in the handlebar and may need the balancing mentioned in this post. I would like to bring attention to the other build, the Schwinn Delmar, with a 3 year old Gasbike 66 with the simple NT carb. This bike uses a wood subframe that hugs the frame rather than tightly clamping to in two narrow spots on the frame. This bike has very little vibration in the handlebar.
The wood subframe is easily adjustable, even on the side of a road, provides a flexible mount for the muffler that moves with the engine, positions the engine away from the pedal chain shield and does a good job dissipating vibration not only making it less annoying, but also protecting the frame. It could be effective eliminating that last bit of vibration after balancing, or if the engine is not that bad, skip the balancing.
If I were to add a gas engine to an aluminum frame; or attempt to mount a 90 cc Lifan or Pitster Pro crate engine, it would most likely have a wood subframe. Looking at posted pictures of Whizzers from the 1940's, I see a similar mounting design, but out of metal.
The wood subframe is easily adjustable, even on the side of a road, provides a flexible mount for the muffler that moves with the engine, positions the engine away from the pedal chain shield and does a good job dissipating vibration not only making it less annoying, but also protecting the frame. It could be effective eliminating that last bit of vibration after balancing, or if the engine is not that bad, skip the balancing.
If I were to add a gas engine to an aluminum frame; or attempt to mount a 90 cc Lifan or Pitster Pro crate engine, it would most likely have a wood subframe. Looking at posted pictures of Whizzers from the 1940's, I see a similar mounting design, but out of metal.
