con-rod materials for a two stroke engine

[Sam_Q]

Now I know this isn't anything to do with Toyota's but I thought I would give it a go anyway because there's some very knowledgeable people on here.

I want to make my own con-rod for a small two stroke engine and I figured that I would just machine it out of a high tensile bolt to make it a decent material. Now I have been assured that it not being forged is not an issue what I am concerned about is that the big and little end bearings are the needle type and directly roll inside the ends of the rod. So for this do I need quite a hard material to get away with it?

Also if I want to adapt a smaller con-rod to the current piston can I make an adapter up with steel or aluminum?

[Duk]

Most (all) bearing race's and journals have hardened layer, so it's probably a very good idea to do the same. Are you able to buy an appropriate outer race for the bearings you intend to use? Failing that, investigate heat treatment that could be done. If you could magically find someone who could surface grind a small bore then you could have them case hardened and surface ground, but...........

BTW, make sure that the bolt that you are using is a propper high tensile/high material quallity 1. Where I work we use lots of larger bolts and when the sizes go up they tend to not be high tensile (4.6 for the big bolts). That may just be cost savings and I'm not saying that big bolts don't come in 8.8 and higher tensile strength, but it is something to be aware of.

[SLO-030]

Could make it out of tool steel.I'm pretty sure you can harden it to make it more resistant to wear from said roller bearings.

Aluminium would just chew out with hardened roller bearings spinning around inside it.

EDIT: Case hardening can be pretty expensive or so ive been told at work.

[Vios-GT_07]

i have a 49cc 2 stroke engine with a seized piston, in bits and pieces..

if you want i can send it to you, but you can't use it as the con-rod bearing has seen bits of the seized piston go through it, and is no longer tight..

it has a roller bearing inside the con-rod, and the weights on the outside seem to be one piece.. not sure if it can be seperated.. pics here

[Sam_Q]

Plonka: running an outer race is not an option because there is very little material as it is in the small end to allow it to be drilled out even further. I was going to drill the "big end" and then hone the sucker with a small brake cylinder hone. Either that or ream it.

SLO-030: I was thinking about this and the only thing that prevents me is I am worried I might harden it too much and make it fragile. I know that two strokes dont have much load on the ends of the rods regardless of the revs but still.. I am thinking maybe if I heat it up cherry red and then brush some oil only on the inside of the big and little end?

Vios-GT_07: thanks but no I have only a 12mm small end shaft and no much room for anything else really.

Now does anyone know if its possible to space out the gudgen hole to fit a smaller pin in there?

[styler]

theres actually loads of technology in heat treatments these days from the old
heat up and quench in oil technique from a few hundred years ago, i went to
heat treatment australia and came back with more brochures than i could read
about different applications and treatments from case hardened to through hardened
to annealing and nitriding, tuftriding etc... unbelievable amount of science in it,
definitely worth a chat for some advice at least in my opinion

[Duk]

I was going to drill the "big end" and then hone the sucker with a small brake cylinder hone. Either that or ream it.

Trouble is, if it's hard enoug to use as a needle roller race than a ram would die a messy death if you tried to use it. Brake cylinder hone is some latteral thinking but unless it's ridgid, it will follow any irregularities in the bore. A small boring head that has some how been fitted with honing stones and a pumped supply of grinding coolant.

After case hardening, how about a die grinder fitted to a lathe tool post, conrod in the (4 jaw) chuck rotating slowly and a nice fine stone with plenty of grinding coolant.
Everythig is ridgid and accurate so you'll get a good finish that is perfectly round.

[Sam_Q]

well come to think of it I will just use my tungsten tipped boring bar in my milling machine and then hone it, but at this stage I feel like this is out of my reach. I might have to make do with the standard rod and adapt the gungen pin somehow.