Dynamic Balance SQ4 Crankshafts?

[Syd.Kallechy]

Hi guys, I have my 58 SQ4 engine in pieces right now and have purchased a set of the new club Con Rods. The paperwork that came with the rods advises dynamic balancing for the cranks...I am having some difficulty finding a shop to do this in the Netherlands and wonder if I could get some feedback from you on your experience using the new rods. I've heard some have just installed them as is and had no problems with vibration ...and others may have had some Vib issues after?

I have weighed and will match rods and piston weights for the cranks. Your experience would be appreciated. Also if you had your cranks balanced can you advise where you had them done (And your experience with the shop?)

Tx

Syd

[david.anderson]

Syd
Did the bike vibrate previously. If not there is no need to balance the cranks again. The balance factor for the one up one down cranks is zero. That is not going to change. The heavier the reciprocating mass the more the vibration. With the new rods being lighter there should be an improvement.Yes I would weigh the rods but would expect them all to be the same. Likewise pair the pistons. If they are different weights remove a little internally from the heavier piston on a lathe till you have a matching pair.
To dynamic balance the shafts will probably mean the roller mains will have to be removed from the drive side and it is difficult to remove them without damaging them. For that reason I static balanced my cranks myself. My front crank was out so I drilled the flywheel at the heavy spot which fixed my problem. I believe my front crank would have originally been right however someone had redrilled the crankshaft oilways and plugged the original oilways. Don’t ask me why as I can see no logical reason. Clearly the oil way changes changed the balance. Static balancing rather than dynamic worked out fine for me, no vibes since.
David

[Syd.Kallechy]

Hi Dave,

I bought the SQ as a basket case so no idea about previous vibration! I also understand that the new rods are lighter and therefore vibs would be less as the original cranks were balanced for the earlier type rods (Lighter than later production versions that I am removing).

I removed the roller mains already as there was a shop in the Netherlands that said they could balance the cranks...however after delivering them a week went by and the shop called me back to advise their weights would not clear the throws on the cranks. So while the weights are off I would like to have the dynamic balance done...problem is I am not Dutch and don't know a lot of any local shops capable of doing the job?

[Vincent.vanGinneke]

Hello Syd,
Just read your pm and saw this notice on the board.
I am not a SQ4 ownwer but if you are sure the cranks have been as a pair I think there's no need to balance .....
however, over here in Holland is Herman Noort who has been very involved in getting these rods production ready.
He has them in his MkI.
Although he has not done much milage yet due to gearbox trouble, he will be able to tell you all about it.
Also in Amstelveen there lives Charles Qua, he also knows a lot about SQ4's.

Vincent

[david.anderson]

Syd
If you cannot find anyone to dynamic balance the cranks you may be able to static balance yourself, or at least check statically. As the 4 is one down and one up crank throws the balance factor is zero.
Make up a frame with 2 narrow straight edges that can be adjusted to be perfectly level from end to end and a suitable distance apart(level across as well) to run on the bearing surfaces. I used 2 steel angles that were perfectly straight. Preferably turn a sleeve with the same outer diameter as the larger bearing surface and slip it on the smaller shaft. If you can’t turn a sleeve then you can set one side higher by half the difference in shaft dia from timing to drive side. It is then only a matter of sitting the crank (with bobweights and flywheel on) on the perfectly level straight edges and seeing if the crank rolls and where it stops. If it stops at the same point every time mark the bottom of the flywheel and drill a small hole. Keep enlarging or deepening the hole until the crank stops at a different point every time. The crank is now static balanced. Static balancing is done in one plane only. Dynamic balancing is done in 2 planes. It is just like having you car wheels balanced with a bubble balance (static) or electronic (dynamic). The dynamic is obviously superior but 9 times out of 10 the static balance will be vibration free.
See the photo for how simple the frame is. I cramp the frame to my lathe bed which is set perfectly level and then I check the frame for level and adjust if necessary.
David

IMG_0475.JPG (74.41 KiB) Viewed 4033 times

[Vincent.vanGinneke]

google Charles Qua on www.virtualindian.org/3techbab.htm
he does this in his home garage..........

[nevhunter]

I think the SQ4 cranks would be balanced in pairs. IF they are a pair all I would do is balance them statically and get the pistons and rods to equal weight. Each end, in the case of the rods. The geared crank arrangement is unique in that opposite forces cancel each other out. Nev

[Syd.Kallechy]

Got the cranks back from the vendor today...plan is to static balance them myself and match the rods/piston Assy weights.
Thanks for the advice!

[Syd.Kallechy]

All thought I would post a few shots of the stand I made to do static Balance my cranks. I made it with some scrap metal Ihad around the shop and only purchased the screws and 4 SKF Bearings (7 Euro each) to build it. Finished it today and did both cranks

[nevhunter]

Knife edges are better. You will find if your set-up works well by how consistently the wheels will come to rest in the same place with a very small amount of out of balance. Good knife edges are virtually frictionless, but you have to have them level and the edge must be undamaged. With ball bearings the smaller the better and the wide contact area is not desireable so you could have a thin edged disc with small ball race in each one . Nev