Balancing a crankshaft

[jpinet]

Hi!
I rebuilding my 127 engine and was wondering if it's worth the trouble to balance the crankshaft with the flywheel and counterweight. I had the crank reground and I'm obviously changing the bearings, but besides that, all's the same.
Opinions?
Also, how do you know which way to reinstall the counterweight on the crankshaft? It can go either way, but because of timing, only one way is good. How do you know?

Thanks!

[ja17]

The front counterweight must only go on one way. Park the first cylinder piston at top of the cylinder and install the front balancer so that the "0" TDC. If the head and cam are installed, make sure that the front two cam lobs are basically upward, the distributor rotor should be pointing to the index  mark (for #1 cylinder) on the distributor rim.

[jpinet]

Thanks Joe.
I have my crankshaft in hand with the engine disassembled. I wanted to get the whole thing balanced and wanted to put the counterweight on the crank while it's out of the engine. What I mean is that with both pins being identical, the counterweight can go either way. I get that with my crank in hand, all I have to do is place it so that the lobe for piston 1 is up and then I'm good to install the counterweight. Just to check if I'm correct, cyl #1 is at distributor end, right?
On that topic, in your experience, is it worth balancing the crank with the counterweight and the flywheel installed? Or is it a waste of time and money?
Thanks again Joe!

[ja17]

If you look closely, the pins on the crankshaft are very slightly off-set. It will go on easily only one way. You can force it on the wrong way, but the pins will be damaged.  Yes lobe for connecting rod #1 will be up when the timing scale is upward 1:00 o'clock (roughly).  If the critical engine parts have not been switched (balancer, flywheel, connecting rods, etc) then balancing should not be needed, but it cannot hurt.

[stickandrudderman]

I always balance crank assembly complete with damper, pulley, flywheel and clutch.
I also get all rods and pistons to within 1g.
The difference is quite noticeable.

[jpinet]

Got it!
I'm not the one who took of the counterweight, so I'm not sure who tight this is supposed to be. Does it need to be 'persuaded' in place? I can't just slide it on the crankshaft. It will need gentle tapping into place. Is that normal?
Thanks Joe!

[jpinet]

I always balance crank assembly complete with damper, pulley, flywheel and clutch.
I also get all rods and pistons to within 1g.
The difference is quite noticeable.

Thanks for this advice!

[ja17]

A good snug to tight fit on the front balancer is good! Persuade it on. Don't pound on the balancer with a hard hammer,  use a softer mallet or block of wood in between. Look in the BBB to see if  your crankshaft, has the "spring washer and crankshaft bolt upgrade"  If your balancer is still nice and tight as you mentioned, and you are not running AC, then the crankshaft dampner pin modification is probably not needed. Be sure to get the crank bolt torqued to specs. If it comes loose it can ruin the crankshaft.

[jpinet]

Joe,

I figured not to bang on it with a sledge hammer, but you are right to mention it. Worse has been done!
I don't have the spring washers, but I'm surprised to see I have 3 washers between the bolt and the balancer.
I'm also questioning whether I have the correct bolt there. I think it should have a stretch bolt, but I have a normal bolt with a lock washer.
Also, all there is on my crankshaft behind the balancer was a 2 cm wide ring, the timing chain gear and the woodruff key, which is fairly damaged.
The EPC shows a 'oil slinger ring' between the spacer ring and the gear and a 'spacer washer' behind the gear.
Am I missing parts or were there differences? My engine ends with 3371 from a 1965 230Sl.
I have no air con.
As always Joe, thanks for your precious advise!

[Benz Dr.]

I find that balanced engines tend to have a lot more low end grunt. I mark everything as I take it apart - it saves a lot of time later on trying to figure out how it goes back together.

[ja17]

Not sure when, but at some point in time, MB dis-continued the oil slinger ring.  Always replace the crank sprocket and spacer ring if you have things apart. The crank sprocket is subjected to the most stress and wear. It has to move all the other engine parts and it is fairly small diameter, so it does wear. A worn drive sprocket will cause increased wear on the new timing chain also. They are fairy inexpensive in the after-market.

[jpinet]

Not sure when, but at some point in time, MB dis-continued the oil slinger ring.  Always replace the crank sprocket and spacer ring if you have things apart. The crank sprocket is subjected to the most stress and wear. It has to move all the other engine parts and it is fairly small diameter, so it does wear. A worn drive sprocket will cause increased wear on the new timing chain also. They are fairy inexpensive in the after-market.

Thanks for the info. I'm replacing all the timing system, including the tensioner. The gears are worn so sharply that I can cut myself on the teeth. And I'm not exaggerating!
I'm a believer that when it comes to gears and chains, or you change the whole thing, or you leave all alone. I found that replacing just a worn gear and not the rest results in undue wear on the new part. Anyway, all is so worn in my engine that replacement is not even a question.

[jpinet]

I find that balanced engines tend to have a lot more low end grunt. I mark everything as I take it apart - it saves a lot of time later on trying to figure out how it goes back together.

Thanks for that input Dan. It costs less than 200$ to get everything balanced, and I figured that since i'm spending close to 10K$ on my engine, what's another 200$? My engine has been tinkered with quite a bit as I could see from disassembling and I'm not sure if I have the original balancer. I think balancing all including pistons and rods will make a difference.

[Benz Dr.]

10K is about average if you do it all yourself. Figure on another 2.5 if you farm it out.

[jpinet]

Dan,
yes, I'm doing most of it myself and in the end, I'll be in for around 10K$
6 new 230sl pistons are not cheap!
CAD$ to US$ exchange these days rate does not help!

I had to have the cylinders resleeved and have oversize valves guides made as the largest oversize available was still too small for both.
This was a very worn out engine.
It was so smokey that I stopped using the car. The moment I decided that was when I parked it next to a terrace in the beautiful part of the old Quebec city last sumer. People are taking in the sun, enjoying their meal and a few comment to me on how nice my car looks as I'm unlocking the door.
But when I started it, the whole terrace became engulfed in a thick cloud of stinking  blue smoke.
I did not stick around!



I'm obviously farming out machine shop work and specialist work, but doing 75% of the work myself.
And this forum and the advice of experts such as you are incredibly helpful!

[jpinet]

Should there be a stretch bolt holding the balancer to the crankshaft? I have a normal bolt with 3 thick washers in there, no lock washer, and it strikes me as odd....

[wwheeler]

You might look at the thick washers closely with a flat edge. They could have a very slight cone. If so, they are the spring washers. When I bought the crank bolt and washers from the Classic Center, I got the stretch bolt and three thick cone washers (Crank bolt # 308676 018001) and (Cone washers #127 993 00 26). This was for a 280 SE engine but I would think it would be the same.

I am a bit confused on the correct way to install these washers though, as I have seen different arrangements. I think there is also something in the BBB about that.