Chrome Crank

[Sonny]

I am currently exploring my crankshaft options. There is the obvious beveling and knife edging, but what about chrome plating? Before I was bitten by the outboard bug I raced an 8 second super pro vega drag car. I distinctly recall spending a crazy amount of money on what was known as a Linati chromeashaft crank and it was a "straight up" chrome crank. But I'm not sure about a 2 stroke, what do you guy's think? I guess my biggest concern isn't any loss of rpm's but rather the oil pooling on the bob weights or counterweights of the crank??...How about the rods too?

[David_L6]

2 stroke VS 4 stroke...

Apples and oranges....

I guess that you are talking about having a crank chrome plated? If so, I don't know if the plating will withstand the needle bearings or not???

I guess my biggest concern isn't any loss of rpm's but rather the oil pooling on the bob weights or counterweights of the crank??...How about the rods too?

Don't worry about that (2 stroke...).

[Sonny]

I know what you mean, I was reading some for the AOF rules last night and they kind of discourage adding any materials like that. And I do realize that there would be no power advantage but I thought maybe a little throdle response, and maybe a little more juice or "smoke" as it is refered to in the corners but maybe not. Yea, chrome is good like that, it will definitly put up with needle berrings, but titanium will not. The other cool thing we used was titanuim wrist pins, much lighter and much stronger, but it absolutly will not put up with needle berrings....bummer.

[sam]

While titanium wrist pins would be way out of line cost wise, I would do something that some of the drag racers are doing to lighten the wristpin part of the reciprocating assembly ...... lightening the wrist pins by taper honing them like a counter sink from both sides. The actual loaded part of the wrist pin is at the connecting rod and the first fraction of an inch on either side of the rod in the big fat piston boss. Out on the edge where the circlip is, there is purportionally less load. Some wrist pins aren't carrying any load at all on their ends and could taper down to just enough edge to locate the pin against the circlip.

I'm embarassed that I did not think of this myself. Steel is much heavier than aluminum and grinding excess weight from the steel wrist pin is equal to grinding a lot more off of the piston with the same effect.

[Sonny]

What are the stock wristpins made of? I know there steel, but are they just run of the mill steel or do they have a spacific designation? after I found out that titanium was out I discovered that the only other option was like a 4130 aircraft steel alloy. Stronger than steel and something like 20% lighter. The plan was to have the new wristpins made a 1/2inch shorter than stock and move the sirclips in twords the small end of the rod a 1/4 inch on each side. but if mercury already uses an high end steel for there rods it would be a huge waist of time and money. That's as far as I got with it, I been meaning to ask someone about what material they used and just forgot. Maybe I could do both the taper hone trick and the short pin with the new material?

[Sonny]

Apples and oranges....

I guess that you are talking about having a crank chrome plated? If so, I don't know if the plating will withstand the needle bearings or not???


Don't worry about that (2 stroke...).

I undestand what you mean as well, but the same basic principals should apply. in one instance you are slicing crankshaft oil vapor and in the other you are slicing fuel and oil vapor in an effort to make a cleaner more efficent crankshaft revolution. I guess it would kind of be the same reason doctors don't use butterknives. but what had me stumped was does the coarse or should I say not smooth texture on a stock crank have something to do with keeping the fuel and oil atomized? or will a shiny glass like surface in there promote the two separating?...counterproductive

[Steve Wilde]

Chromed crank

Chrome plating will not hold up under the extreme pressure of a needle or roller bearing. Chromed journals hold up with plain bearings because the unit pressure is much less.

[seagull170]

Here in the UK production wrist pins were often made of one of the case hardenable steels EN24T or EN40 type so that they could be machined over size on the diameter circa 40 thou, then heat treated so they had a hardened layer about 40 thou thick, this often produced some minor distortion, then they were ground back between centers 20 thou to the finished diameter & straightness.
Though modern production methods & materials will permit current large volume production to do this in 2 steps with chemical hardening.
I often lighten wrist pins by reducing their wall thickness, at the risk of some flexing, though most manufactures used a pin that would fit a range of pistons with varying loads so they were often heavyier than needed, but were cheaper.
Remember if you lighten the pin & then lighten the piston to reduce pin load you run the risk of changing the crank balance factor.
I can't see any benefit in chroming a 2 stroke crankshaft, the fuel mix can't see a mirror finish, the crank would have to be polished first anyway, just leave it at that.
Here damaged journals can be hot chromed sprayed & then reground leaving them with a hard finish suitable for loose & caged needles.
Some where over there in the States is the owner of a 1930's Marston Seagull twin if anyone knows who it is, please let me know, so that I can remanufacture the missing waterpump bits for mine, or at least know what they looked like.

Charles Large