Grimgrak

iTrader: (3)

How many of you are running evo 6 rod bearings because they are wider?

LetsGetThisDone

iTrader: (1)

You woulduld have to measure the crank to see if the journal is wide enough. It's a good bet it will have to be widened. Side clearance on the bearings plays a major role in oil retention for the bearing, so an appreciable difference in bearing width will likely require crankshaft machining.

tscompusa

iTrader: (31)

You chamfer the bearings to work with the crank. I've done it on one 2.2LR 159mm rod build only. We stick to standard width bearings, I see no reason to use the wider. Had zero failures with evo width.

LetsGetThisDone

iTrader: (1)

If you chamfer the bearings you're not taking advantage of the extra surface area, so it would be pointless to do that...

Not saying the extra surface area is needed, but if that is what you're after, you would widen the journal, not chamfer the bearing.

tscompusa

iTrader: (31)

When you chamfer the bearing you are only taking thousandths of an inch off each side.

Cutting the crank journal radius and cutting into the journal is the wrong way 100% to go about it.

The 6 bolt wider bearings are a lot wider then standard size. More surface area is also a plus, but again not necessary.

I could have a crank made out of titanium, but if the cheaper billet does the job why bother.

poonpower

so you are saying machine the bearings to fit the crank. What is the tolerance between the bearing and the crank?

LetsGetThisDone

iTrader: (1)

You have to narrow/chamfer the bearing to fit in the journal with proper side clearance, so no matter what, what you're doing is making all of the work 100% pointless because you now have a bearing that is the same width at the interface with the crank as the bearing you could have used that required no modification.


And you can definitely widen a journal. I've done it. When I was testing using ford 4.6L rods in the ford SOHC V6, we built one with the big end of the rod machined narrower to fit the crank and stock bearings, and one with the crank rod journals widened to fit the rod and a wider bearing. Both are still running and have been torn down and put back together twice to check for wear. If I built another one, we will just narrow the rods because it is much less expensive than having the crank cut.


I'm not sure the titanium crank reference means anything, we're talking about rod bearings..

tscompusa

iTrader: (31)

The crank reference was an example that we do not need the wider bearings when the standard width works just fine. So I was suggesting the wider surface area is better, but not needed to function properly.

Correct in thinking the side clearance is dictated by how the bearing sits on the journal, but in reality technically speaking, side clearancing a rod at the cap and chamfering a bearing to fit a journal are two different things. Ones making it so the bearing doesn't get caught on the journal radius itself when tightened down, and the other is clearancing the rod cap to the crank web, but in turn, the bearing clearance moves with this as well. so yes both work together to achieve proper clearance. Just trying to be as descriptive as possible.

Show me a crank you shaved the radius down to make a bearing sit flush I want to see this, or find me articles that say they would prefer cutting into the crank journal vs chamfering some odd .050" max per each bearing to make it work.

I think you'll end up finding most people just clearancing the bearing to work with the radius of the crank vs cutting into the crank.

Cutting into a crank is pretty dangerous and you can destroy the crank.

I only ever chamfered bearings on one engine, which runs flawless and ill be sharing its results soon, but since then we just use the regular proper size bearing for what the crank was designed for.

If cutting the crank is easy and cheap sure that's better then chamfering the bearing, because you would have more bearing surface then to work with, but you do realize if you want to cut the crank flat to not lose bearing surface, you are literally expanding the width of the crank where the manufacturer stopped and started the radius?

Go look at a 7 bolt crank and a 6 bolt rod bearing, and play with them and you will end up agreeing with me that cutting the crank is suicide to make it work vs chamfering the bearing.

I don't care what ford you worked with, or anything that's not relevant to what were talking about here. Were talking about making a 6 bolt rod bearing fit into a 7 bolt mitsu crank rod journal. What you worked with might have been a lot different scenario then whats required for this.

tscompusa

iTrader: (31)

That statement I highlighted in bold indicates you have no idea what I'm even referring to. At least it is completely irrelevant to this particular issue.

The issue here is the actual bearing sitting on the rod journal. Where the end radius is on the rod journal the bearing is trying to sit flush against. So as you can imagine, when tightening down the cap, the bearing is pushing against the radius edge corner curve and binding up.

You can do all the rod cap clearaning you want, you aren't going to fix this issue without actually taking material off the bearing itself, because how the bearings trying to seat is the issue here, not the rod cap itself. The bearings to wide.

Hopefully you get what im saying now. The bearing is to wide to sit in the journal!

LetsGetThisDone

iTrader: (1)

The crank we cut was .062" per side, being an American V6 engine, it had plenty of meat. The rods that were narrowed for the uncut crank were cut about the same. There was no chamfering the bearing to fit that width disparity. I don't have pics of it. When I built these motors, I was working at a shop building race engines, and the owner was doing a lot custom intake manifolds with interchangeable runners, and badass throttle bodies, and cylinder heads with his own port designs for LS motors. So we didn't exactly document what we were doing with a bunch of pictures.


I said that statement because you said cutting the crank was a terrible idea. That V6 I described, the rod and bearing were about .125" too wide because they were for a different engine. I brought narrowing the rod because we built them both ways. Narrowing the rod and using the original bearing to fit the crank. And widening the crank to fit the new wider rod and new (wider) bearing. You could very easily take journal out a few thou wider to make room for a wider bearing.

tscompusa

iTrader: (31)

Ok my bad I read the statement wrong then.

For this particular application I did, we had to remove .025" per each side.

Cutting the crank just seems kind of scary to me instead of chamfering the bearing.

Like I said though, I agree with you cutting the crank is working with the bearing surface actually taking advantage of the bearing being wider, vs narrowing it down and almost turning it back into a 7 bolt bearing getting you little gain in return.

Don't take anything I said the wrong way, I wasn't trying to be rude when I brought up the Ford thing, Just trying to make sure were both looking at it the same way with the same application.