Walked 7bolt 2.4 Results

Raptor · 10-04-2004

Okay, finally Chris's walked 7 bolt 2.4 is torn down and the reasons for it's problems can be assessed. All the bearings in this engine look like new with the obvious exception of the thrust bearing. The block is perfect and suffered no damage as the bearing still had adequate material on both sides to protect it. The remaining thrust surface on both upper and lower shells are exactly the same thickness which means that they were not out of alignment in any way. There is no difference in dimension from side to side thickness meaning they were not cocked to one direction or the other and when assembled without the bearings, the thrust surfaces on the block and the cap line up perfectly with very little movement possible due to the CRCO bushings. Now what caused it to wear? Well, as said before, the rest of the bearings are in perfect shape so there could not have been oiling issues at least in the main galley. The only thing somewhat obvious is the wear on the crank itself and the bearing. The bearing should have worn much furthur than the crank but it doesn't look to be the case. The crank has a fair amount of wear for the amount of damage to the bearing. That does support the case that the 7 bolts have looser/weeker grain structure in both the block and the crank and are most likely more effected by the heavy clutch pressures than the 6 bolt blocks/cranks. I would hope the cranks are nitrided equally on the thrust surfaces, but maybe they are not.

We are going to try using H rated bearings and having the crank repaired if possible. The clutch is being replaced with a twin disc and I am hoping that that solves any furthur issues with crankwalk on this engine at least.

Any useful input is welcome. Any stupid input will be dealt with accordingly.

Enes · 10-04-2004

stupid coment insert here...

I hope this engine is salvagable..
do you guys know what year this engine was from? because suposedly 99's had some changes done to them?

-E

Raptor · 10-04-2004

The engine itself is fine, the crank however is not without a rediculous amount of money. We did find a reasonable one already though so it's all good. I have not done any searching on what the factory does for nitriding on the 7 bolt 2.4's, would anyone happen to know off hand?

Enes · 10-04-2004

so basicly the passenger side of the crank inner bearing was getting worn out?

**JET** · 10-04-2004

There was talk of crank differences on NABR. It looks as if the 7 bolt cranks may not be nitrided at all! This isn't a very scientific test, but if a 7 bolt crank is left outside for any length of time, it will rust. You can leave a 6 bolt crank outside for years and it looks like new.

Allan was supposed to take my 6 bolt crank that walked several months ago. It sat ouside for about 6 weeks. It looks like new except for the surfaces that were damaged from the crank walk. So there is definately a coating on the 6 bolt cranks.

Also not totally related to this situation, but another data point to look at. When my engine crank walked it wore much worse on one side than the other. The bearing was still about 3/4 original thickness on one side, but wore into the block a good .030" on the other side.

I am thinking you should have the new crank sent out and nitride coated, because the 7 bolt crank is either not coated or it has a substandard coating that is causing a problem. This is just my 2 cents, YMMV.

JET

Enes · 10-04-2004

i tought your crankwalking issue was a trany install problem?

-E

LightningGSX · 10-04-2004

So the H rated bearings are just a harder material right?

Raptor · 10-04-2004

Yep Eric, they are a higher load bearing, originally designed for use in Nascar. There is info on several bearing manufacurer sites. Worth reading. The bearings we are going to order are ACL's from Austrailia.

JET, I don't doubt that what you say is true, I believe it has a lot of merit. The wear on the crank is pretty extreme for the damage to the bearing. The crank is pretty soft is the only conclusion I can make based on what I saw. The thrust surfaces on the crank were in very nice shape when it was put together. I have a place to do the nitriding and then it will be sent to gopher to polish all the surfaces including the thrust areas. It is pretty normal for the bearing to wear on one side(flywheel side) more than the other with a heavy pressure plate which is the case here as well.

And Enes, you are a gutsy Bosnian bringing that up again :stick:

**Goat Blower** · 10-04-2004

Well, being that bearings are pretty soft, I'd say the 7-bolt crank is awfully soft if it has a lot of wear on it. Nitriding was about $180 when I had it done, but that's a deal compared to completely switching motors. Make sure you throw away the oil cooler if it's an external.

slowbubblecar · 10-04-2004

Quote:

Originally posted by Raptor@Oct 4 2004, 08:33 PM
It is pretty normal for the bearing to wear on one side(flywheel side) more than the other with a heavy pressure plate which is the case here as well.

Mine wore about the same way as this with the stock clutch and pressure plate. They were all worn but that end was a lot worse. I am sure mine wasn't from the pressure plate though. I also had a bad ring and lost the #1 cyl rod bearing also. I wonfer what other reasons there are for that end being worse.

LightningGSX · 10-04-2004

I don't know much about this subject.But its seems to me the hardness of the bearing surfaces would be somewhat meaningless.Since they ride on oil and not the actual bearing surfaces.I would think you need more thrust surface area and not harder bearings.

Enes · 10-04-2004

i wasn't involved.. nor want to get involved.. i was just stating what i have heard pretty much from anyone i've talked to

i won't mention names.

-E

JustROLLIN · 10-04-2004

Quote:

Originally posted by LightningGSX@Oct 4 2004, 09:19 PM
I don't know much about this subject.But its seems to me the hardness of the bearing surfaces would be somewhat meaningless.Since they ride on oil and not the actual bearing surfaces.I would think you need more thrust surface area and not harder bearings.

Agreed. Bearings work on a "full-film" style lubrication. I guess I really dont see the advantage to a harder bearing either. I suppose it could make a difference on start-ups or if you have very low oil pressure for some reason. Mike, wanna explain a little further?

LightningGSX · 10-04-2004

Another question, I've heard of a few different nitride coatings, which one do they use on automotive shit?

**Shane@DBPerformance** · 10-04-2004

The bearing is supposed to keep a layer of oil film between the crank and it, but as Mike is saying, with a 2600lb, 2900lb+ pressure plate maybe that layer of oil isn't exactly staying there when the clutch is pushed in.

Emcee gsxtc · 10-05-2004

Quote:

Originally posted by ecoli@Oct 4 2004, 10:59 PM
The bearing is supposed to keep a layer of oil film between the crank and it, but as Mike is saying, with a 2600lb, 2900lb+ pressure plate maybe that layer of oil isn't exactly staying there when the clutch is pushed in.

Lets hope thats not true in all cases. I am running that clutch and would flip if crankwalk took my motor before overboosting did.

SlowWhite · 10-05-2004

What's the cost to have new bearings put into a motor?

Raptor · 10-05-2004

The interesting thing about the way the bearing was worn was that it was more on the outer diameter than inner (closer to crank journal) the reason that is could be from a number of things, but I have my own theory on it. As you said the thrust surface relies on a very thin layer of oil which would keep the bearings suface separated from the crank surface. That can only happen if both surfaces are perfectly square with each other. If one surface is able to flex even .001" the surface would no longer be square and the oil would have an exit path as well as a higher point to sheer the oil from. If that were to happen even in a small amount, the contact created wears the crank then the surface is rough and oil sheer is pretty much guaranteed. When installing the crank, you put pressure on the flywheel end of the crank to align the thrust bearings before the cap is torqued to make sure there is a flat surface as well as making sure the thrust surface that recieves the most load is up against the main web so it has support to keep it from flexing. That is all fine in a normal environment where there isn't excessive pressure beyond what the engineers had in mind for the engine and size/strength of the bearings. With the increase in load, on the bearing surface, the only way to compensate would be to use stronger/harder materials to prevent any possible flex or wear. That is why the h rated bearings make sense. Also having the crank nitrided if the surfaces are soft makes sense.

All the "definitive" answers everyone comes up with havn't exactly been proven without question so I have to go on the observations I make and what I believe makes sense from others experience. I believe H rated bearings, a nitrided crank and lighter pressure plate force will solve the issues.