connecting rod question

Topic: connecting rod question (Read 1349 times) previous topic - next topic

connecting rod question

March 06, 2005, 12:02:42 PM

are there any engines out there not using flat bearings like in the engines we typically deal with?

Re: question

Reply #1 – March 06, 2005, 04:55:34 PM

I dunno about cars but my old Arctic Cat snowmobile used roller bearings. The crank was pressed together and had to be disassembled to get a rod off (the rod did not have a removable cap). I'm sure most two-strokes would be like this

Re: question

Reply #2 – March 06, 2005, 06:01:56 PM

some weed eaters like my eager beaver has needle bearings where the rod / crank attach.

anyways.......the below rods which would be one off,, whatchall think? Since there really aint no such thing as a roller block if we still have the friction type bearings.

any votes on needle or ball bearing?

Ill have to pretty much explain right off the bat that there will be no need for oil passages on the crank to block or crank to rods cause it will be dependant on the slingers. with these, you'd never maintain oil presure so plug it off. mill the block and custom make main caps to match.

Re: question

Reply #3 – March 06, 2005, 07:02:13 PM

The biggest problem I can see with that is the seam where the bottom end of the rod is split. No matter how well you machined that hole, with a seam in it the bearing will fail. The seam could be finished down to the microscopic level, but those rollers passing over it would widen it up in short order. I would guess that's why my old Arctic Cat had a one-piece rod with a pressed-together crank.

Now, that being said, you could use an outer race to eliminate the rollers coming into contact with the seam (like in a rear end) but you'd still have to press the crank apart and together to remove/reinstall bearings.

And with that being said, I'm not sure there would be much of a benefit. With conventional engine bearings there is no metal-to-metal contact. A thin film of oil supports the crank and keeps it separate from the bearings. The only time the crank contacts the bearings is when the oil pressure drops or when the crank is over-revved. This results in the crank "welding" itself to the bearings, causing the bearing to spin in its seat. Once it spins it blocks the oil passage and you end up with a ruined crank and bearing. Under normal operation, even under severe load, the crank should never touch the bearing.

In a two-stroke engine the rollers are necessary because there is no oil in the crank case. All two-strokes have their carburetor (or throttle body) mounted directly to the crank case. Fuel mixed with oil is brought into the crankcase, and the heavier oil falls out of suspension and coats everything with a fine lubricating film. The film is not thick enough for "friction" bearings, nor is it under enough pressure. The oil is constantly being replaced (and burned, hence the blue smoke), so you'll never find more than a few drops when you tear down an engine.

Now, while we're thinking about alternative bearing types, why not magnets? If magnets can suspend a train they could support the load any crank would have on it...

Combine magnet bearings with ceramic cylinders and you'd have a very efficient engine (ceramic would retain heat rather than waste it in a cooling system) with no need for lubricating oil.

Re: question

Reply #4 – March 06, 2005, 09:28:58 PM

Oh,,
did i forget to metion the bearings would be teflon?

on a side note, i only brought this concept up because ive seen the application everywhere in highspeed devices including tranmissions and wheel bearings.

magnetic bearings ,, a whole crank would have to be magnetized and the rods as well. Very interesting,, your a thinker man!

Re: connecting rod question

Reply #5 – March 20, 2005, 12:55:33 PM

i know this thread is a little on the past history side but i have one point to make that really bugs me.

How is it that an idler pully like found on the 3.8 or the 5.0 can for the most part remain unlubricated and last so long?
with that thought, it makes you wonder if needle bearings on connecting rods would work or not buy the use of the crank slingers alone.

This thought hit me when i was out in the garage and i saw my old 3.8 idler pully and it lasted for id say about 200kmiles.

im still scratching my head on this one taking in account its rpm is greater than the crank!!!!!!!!

Re: connecting rod question

Reply #6 – March 20, 2005, 01:04:04 PM

The idler pulley bearings last so long because they're permanently lubricated, and even though they spin faster than the crank, they're under very little stress. Just imagine the pressure a connecting rod is under

Re: connecting rod question

Reply #7 – March 20, 2005, 09:29:17 PM

I do rember reading that some people have made the cranks roller but it costs a shiznit load. U can get roller cam bearings and that is a good penny too do.