I'm considering installing some bolt on crank shaft counter weights in my 26 engine. There is some vibration that I can't seem to get rid of at the higher end of the operating RPM. I don't think my clutch is slipping and I have a new 4th main, new drive shaft and brass bushing/modern thrust bearing. It vibrates with the trans in neutral as well. I know there are other causes of engine vibration but right now, I'd like your knowledge and experience with the counter weights. Thanks.

Dad has a set of the bolt on counterweights on his '14 touring. That engine was in my '15 touring previously. It has at least 20,000 miles on it with no sign of trouble yet. The counterweights were bolted on, then the reciprocating assembly was balanced. After that the transmission was balanced. The two assemblies were bolted together, and balance was checked prior to engine assembly.

My opinion, the bolt on counterweights don't alleviate the need to have the engine balanced. They just make it easier. I would not expect good results bolting them on an engine in the car.

I would not consider bolting on counter weights unless I was going to have the entire crankshaft with the weights balanced as a unit. No one will ever convince me that they can be pre-balanced and bolt on so perfectly centered inside the engine to not need a proper re-balance.

A side story, A very good friend of mine years a go bought a speedster that had the counter weights on it. He drove it and enjoyed it for a couple years. A weekend or so after a big speedster meet, the car was in his driveway while he was working on it, tuning it up, cleaning it. He gunned the engine and one pair of weights went flying. One took out nearly the whole one side of the block and dented a chain link fence about thirty feet away.
It turned out to have the wrong bolts in it.
Drive carefully, and enjoy, W2

You can't use the bolts that come with the weights. They are grade 5, and to soft. We use Cat. bolts, and nuts.

Don't expect to fix an out of balance engine with just Dunn weights, you have to start deeper then that.

With that said, we have put on about 150 plus sets of Dun weights.

The biggest thing besides balance I can see, is when shifting from low to high, the weights take out the buck that you get until the speed increases in high gear.

can they be used on a 26-7 crank, or does it have to be a diamond shape where they bolt on crank ?

Mr. Kohnke - You said,....."we use Cat. bolts, and nuts". Call me stupid I guess, but I have no idea what that means. (???)

Cat.com bolts

http://parts.cat.com/parts/hardware

They can be used on all cranks, and should be checked for fit on all cranks.

If you are going to use them on a new rebuild, the best way is grind the rod pins, fit the weights, and then grind the mains.

I will call Cat tomorrow, and find out which numbers on the parts card are the order numbers, as there are a bunch.

Cat. Number for bolt 3" bolt is 8S4726, 3"x 7/16 fine.

Cat. number for castle nut is 4B6072, 7/16 Fine.

The 3" bolt is long enough for the Bolt, and just the nut, and you drill the hole in the bolt where the nut ends up at, for the key.

You can also use a 4" bolt with a lock washer on the bolt, slide the bolt through the weights, add another lock washer, and nut, tighten the nut, drill the hole for the pin, and cut the left over bolt off with an air disk.

I do not have the part number for the 4" bolt, but they are easy had from Cat.

Thanks guys; from what I read on the Caterpillar web site, these bolts are even superior to standard Grade 8 bolts. No wonder Caterpillar has the fine reputation that they do!

I don't know about now, but back in the '80s and '90s, Caterpillar bolts were the best bang for the buck for standard sized bolts. Dave

I would be really interested in WHY in Herm's opinion the grade 5 bolts are not strong enough. Based on any situation I can come up with the load on these bolts will never come close the strength of them. I have had a set in service for over 30 years and countless thousands of miles. Certainly you don't want to over torque them on installation, but that applies to any bolt installation. These weights are problematic to install as they can easily put unnecessary stress and distort the crank if they are not properly hand fitted to the individual crank. I have seen them cause significant bending of a crank if not properly fitted (which takes time to do right)

Here's a Forum link from several years ago on the Dunn counter weights.

http://www.mtfca.com/discus/messages/80257/118596.html

The bolts stretched, on the 5th, 1/2 set came loose, and slipped back and forth about 1/4 inch. Nothing hurt, but made noise, so once bitten!

I am not saying that all will come loose, but why take a chance with someone's motor. The Cat bolts we use, are also Rod bolts, and Nuts, is what they told me.

Also, when we removed the set that had NOT come loose, they were torqued to the 80 pounds that they had been. Using the Torque wrench, then came out to 40#.

As I have said in past posts, we Grind the rods, install the weights, and then grind the mains, then cut the O.D. of the swing in the lathe if needed, and then spin balance.

Herm.

Herm, is there any Cat bolts that will work for the wrist pin bolts?

Ken T,
I was wondering the same question.

I never have checked that out. I use good used ones with a new lock washer.

I took that bent hair pin Henry laughingly called a crankshaft out of my T and pitched it! Replaced it with a nice heavy duty balanced Model A crank. Reworked all of the bearings and their caps for the A crank and never worried about it again. Runs a hell of a lot smoother. Also helped putting those little scoops on the end of the rod caps too.

Torquing a 7/16" grade 5 bolt to 80 ft lbs would certainly explain the persons problem. I am amazed that they could get to that torque at all on that bolt. I suppose they got close and then "adjusted" it to get the cotter pins in as well.

Martin
Did you drill your A crank for pressure oil? Not too hard to do. I have bolted counterweights on to a A crank with good success.

Les, the 80 pounds has nothing to do with it. The threads were not pulled, but the bolts stretched, past what ever torque would have held it. They just plain won't work safely.

Many connecting rod bolts, and main bolts of that size are pulled to 100 pounds.

That's the whole point, the bolts were to soft for what they needed to be.

That is why the Cat Bolts.

When Gas Light first came out with them, 47 plus years ago, they always came with bolts that a file wouldn't touch, and then changed over to the softer ones maybe give or take 25 years.

The recomended torque for a 7/16 UNF grade 5 bolt is 55 ft lbs (it is only 50 ft lbs for a UNC). If the bolts were grade 8 it would be 78 and 70 ft lbs respectively.
A 1/2" bolt would be 90 for UNF and 80 for UNC for grade 5 and 110 for UNF and 98 for UNC for grade 8.

For a file not to touch a bolt there are two possible answers that come to mind;
1. The bolt has been hardened for wear resistance which in no way increases it's strength.
2. Buy a new file!!!

A grade 8 bolt files just fine. I can not comment on Caterpillar bolts although I have a good friend who bleeds "yellow" so I will ask him when I get home in a couple of days

Generally speaking if a bolt that has been hardened for wear resistance it would not have as good a fatigue resistance and so would be a poor choice for any application having cyclical loading (such as would occur on a crankshaft application).

You seem to be implying that a harder bolt is in some way stronger and this not correct.

Yes I have worked on engines that are torqued to over 100 ft lbs. In fact that main bearing bolts on my 5 main model T are torqued to over 100 ft lbs. They also happen to be 9/16" socket head

Les, you are in your own little world.

I didn't say they were Grade 8

I didn't say anything about hitting them with a file.

I told you what I did, and how it worked, if it doesn't fit your approval, I don't know what to tell you!

I have a used set of, what looks like, original Dunn counterweights that we just took off a 26 engine. I don't know who rebuilt the motor before I got it, but the main bearings are all different sizes and the rods were a mess, too. I had a Suremike crank that had been magnafluxed, so we used it, after repouring the mains. Of course, as others have said, any counterweights should be balanced with the crank and related parts, whether they are new or used.