Crank balance on an oilhead

[rzleo]

Has anyone balanced a crank on a R1100s. if so was it very imbalanced while still stock. I was told mine was very imbalanced. does any know a good ratio.

[roger albert]

Did the person who said this not like the balance of the crank itself (i.e. throws of unequal mass or not degreed 180 apart, or did they not like the balance _factor_ of the pistons vs throws?

Are they boxer savvy and realize the rocking couple is not going to go away?

[BMW Atlanta]

of the few oilhead crankshafts we have had sent out, they all benefited from balancing and there's alot of weight there to be shed if so desired as well.

[JonyRR]

so bobby; did they change the balance factor at all;p lease expound on this as I intend to do this also..ideally with an R1200C crankshaft.

also, if you wouldn't mind can you give us a brief rundown on breaking in a touratech ceramic clutch disc?
Mine's still sitting on the bench along with a bunch of other parts,waiting for my xmas vaca period so I can concentate on some uninterrupted wrenching in the jonyrr batcave

[JonyRR]

that's 'concentrate'...*hic*.
my christmas party's starting shortly and I have to achieve the correct altitude/attitide for later. A cannon awaits, but that's another story...

[rzleo]

I am not exactly sure. Chris at SJbmw told me. I think it was so far off they thought maybe it was designed that way. Balance factor was mentioned, i believe he said it was 7% off, or 7% and it is suposed to be 50% not sure had a few cocktails prior. I don't know much about the balancing of a motor. If anyone has a good norcal crank shop, who will know this engine, let me know.

[markjenn]

Don't mean to hijack the thread, but I've always wondered why someone doesn't built a boxer where the connecting rod on one side is "forked" with two big ends, so that big end on the other side goes between the forks. This would allow the two piston bores to be on the same centerline and eliminate the rocking couple vibration that plagues the boxer.

- Mark

[BMW Atlanta]

Originally posted by markjenn
Don't mean to hijack the thread, but I've always wondered why someone doesn't built a boxer where the connecting rod on one side is "forked" with two big ends, so that big end on the other side goes between the forks. This would allow the two piston bores to be on the same centerline and eliminate the rocking couple vibration that plagues the boxer.

- Mark

Has to do with firing cycle. That configuration would work if we made the boxer a 2 stroke, imagine that! Because the 4 stroke has to have one clean stroke where no ignition/combustion occurs the pistons need to be at top of the stroke together in order to alternate firing sequence every 180 degrees. With double connecting rod and the pistons opposing eachothers stroke on a 4 stroke, you would have combustion at 0 and 90 degrees, but nothing at 180 and 240 which would make for a surgning boxer.


As for the balancing of the crankshaft, I'll have to get back to you on the desired specs. We outsource all of our maching and have a good ole boy atlanta network that manages to do us proud from time to time.

[roger albert]

On the two stroke solution Bobby mentions, the uneven firing would be the least on your troubles. The balance would be the real issue. You'd lose the small rocking couple, and gain a massive primary imbalance. Like a big single.

On the fourstroke, it's undoable only if you're limiting yourself to a single (shared) crankpin and forked big-end, as Harley does.

A German tech college did some work on this maybe 7 years ago or so, and I corresponded with the professor a bit on it, and I'm 90% sure, posted here on it. Their solution preserved bore alignment by using two separate full length (but narrow) con-rods on one side (same total mass) that were anchored on two small crank pins (also half width) on either side of the full size crank pin for the other side.

If I recall correctly, they did manage to get it running and bring the project to completion. I believe it was an early oilhead motor that was modified (radically) but am not sure. Their solution's spacing, like other boxers, of course precluded a center bearing, but it was said to work well. I dont' think it was published, but when I talked to the prof, he indicated that it not only eliminated the rocking couple, but in doing so, would also reduce crankshaft bearing wear since the crank ends would no longer be pulsing left and right. In an all new design, it could also have allowed for a shorter/stiffer/lighter crank and crankcase with bearings having smaller dimensions, but the same as 'normal' wear and load capacity. The project ended before that could be proven. I gathered, due to funding.
I think they translated it as in-line boxer.

Good reading if you can find it, but not well publicised.

My memory is a little fuzzy on this so I might not have the details perfect, but, it has been done.

[kpolito99]

Wow! Resurrecting this thread from 8 years ago to ask if anyone has had any more recent experience with balancing the crankshaft in a boxer engine (specifically an R1200S).

I am investigating upgrading the pistons and rods in my R1200S and understand that adding the Wossner components will result in a significant reduction of the reciprocating mass.

Falicon Crankshaft in Clearwater, FL has quoted me $275 to re-balance my crankshaft for use with the lighter pistons and rods.

Has anyone else had their crankshaft re-balanced?

It seems that several forum members have reported a huge improvement in how the engine performs after simply adding the lighter rods and pistons. While it does not seem like re-balancing is essential I would like to learn more about the added benefits if anyone has first hand experience. Thanks -

[oneye]

My two cents for Falicon: I built a 270-phased Yamaha XS 650/840 and had them balance and weld the crank -- excellent work and good customer communication.