91 replies to this topic

[Terry Haines]

....from the UIM it looks like an early unit.

[KAOS_2.5M]

spridget, on Jul 7 2008, 05:54 PM, said:

sorry, i thought he had an '03 engine.

naw, 02 sable engine

when you say dom "doesn't even bother" those bolts, does that mean I can just run without them?

[Terry Haines]

...well I guess as we have no more questions and comments on rod/main bearings I should leave it at that eh?
Would a best case summary assist or just leave it 'as is'. I hope this post has given some good info and also why the later oil pan etc etc is not going to stop a spun bearing.Save your $$..maybe for some rods!!!

[KAOS_2.5M]

Terry Haines, on Jul 9 2008, 12:39 PM, said:

...well I guess as we have no more questions and comments on rod/main bearings I should leave it at that eh?
Would a best case summary assist or just leave it 'as is'. I hope this post has given some good info and also why the later oil pan etc etc is not going to stop a spun bearing.Save your $$..maybe for some rods!!!

I learned plenty of good info in here, and now I know basically any duratec could spin a rod soon as it gets the miles up there, which is really important to know.

good thing I got a 37k mile engine now

thanks terry

[Terry Haines]

...so to sum up on bearings:-

*The ONLY thing that retains main and rod bearings in the housing is BEARING CRUSH.
*Without it or incorrect specs of it the BEARING WILL SPIN.
*Reduction in bearing crush can be caused by-
-Incorrect parent bore dimensions of the housing (Too big)
-Incorrect bearing liner thickness.
-Deformed or fatigue on the rod or housing causing increase in internal diameter and reduction in crush.

That is IT.

We can go back to the start point on types of bearing material etc but again I add that ANY BEARING MATERIAL WILL SPIN if
the assembly does not have correct BEARING CRUSH.

I'm in touch with friends at Mahle to establish some 'rules of thumb' for the crush etc on 2.5 & 3.0 engines...but as I stated,with a 'cracked' PM rod almost impossible to measure the 'stand proud'/ crush on this type of rod.

[Terry Haines]

....maybe I should add here that the correct amount of 'crush' per liner for a 2.5 or 3.0 is 0.005" per liner.
This is around the norm for most rod bearings.Examples being, early BMC Mini engines at 0.004">0.005",
Ford 'Pinto' style OHC at 0.003">0.006" per liner.My data for our V6 is from Ford and Mahle.

[Terry Haines]

...as we have touched on PM (powder metal) conrods,I found this most interesting and how it can relate to the quality and durability of such PM parts. This is a brief extract from the text in this months 'Race Engine Technology' mag. BTW this process has only been around since 2000 so I doubt any of our PM rods from Ford use it...


Powder Metal technologies have come a long way since their introduction before the Second World War. Aluminium alloys made by the Powder Metal (PM) process are, in some areas, out-performing conventionally produced materials. However, these improved performance qualities have not been constrained to aluminium alloys alone. With its third generation PM processes, specialist steels manufacturer Bohler Uddeholm is producing high performance sintered steels that go beyond anything that can be offered by steels produced by conventional processestion .
Early PM steels, though easily pressed and sintered, suffered from a lack of strength and ductility when compared to conventional wrought steel alloys. The manufacturing process involved water atomisation of a stream of molten pre-alloyed steel to produce irregularly
shaped particles. The powder was then pressed into the rough initial component shape, after which it was sintered to produce a part that could be used as it was or machined to final shape.
With these early production processes, it was not possible to obtain 100% densification of the material and although the process allowed the production of homogeneous alloys of exceptional hardness and wear resistance, they were not suitable for use where sustained high impact loads were found and ductility was required.
This lack of 100% densification does, in some cases, have some advantages, for example, in the production of sintered valve seats where copper can be infiltrated into the material matrix to give it much improved conductivity, or in the case of valve guides the sintered material can be infiltrated with graphite to enhance its resistance to seizure. However, in the case of high strength alloy steels, nothing less than 100% densification is acceptable.
With the introduction of its 'Microclean' third.generation highspeed steels, Bohler has raised the bar for high performance steels.

[mikey]

Terry,

This was an extremely good thread, a bit dry, but very very interesting.

I do have one question though. Unless I read it wrong, you stated that lack of oil never causes spun bearings.
Granted my experience with engine rebuilding is miniscule when compared to yours, but with lack of oil the metal on metal friction can create a huge amount of heat that actually weld the bearing to the journal and can over come even properly engineered bearing crush.
I've pulled engines apart and actually seen the bearing welded in this way...never one of our V6's though.

I have also seen bearings installed with the oil hole in the wrong spot (not mine thank heavens), without the oil the bearing didn't last long at all.

One other comment that I don't think was mentioned was that with powdered metal rods, the one piece rod is pressure fractured into 2 halves creating uneven mating surfaces and must only be installed with it's mated half.

Thanks for the great info!

Mikey

[2000SVTC]

I obviously cannot speak for Terry, but I'm sure his point is that - on these engines - spun conrod bearings are typically caused by lack of crush, caused by deformation of the big end ID of the sintered conrods. And thus fixes involving lubrication will be ineffective.

I've got a question for Terry too -

I've recently seen conrod bearings listed for our engines that have an oversized OD, +.002" I think. I assume that this is to overcome the inability to do a traditional rod recondition on the "cracked" rods. So presumably one simply hones the big end oversize, thus making it round and correctly sized wrt crush.

At some point I am going to pull the trans on my SVT and send it to Terry for a rework. My engine - with 113k miles - is in good shape, but the threat of conrod failure if I run it hard is unnerving. I really don't want to spend a bunch of money modding the engine, but wonder if a preemptive conrod rebuild is in order. It shouldn't be too hard or costly - if the engine is already out - to pull it down and remove/replace the conrods and bearings. Assuming bores are good, a set of rings and valve seals and it should be good for another 100k...?

So my question is - would honing the big ends on the existing conrods be a reasonably effective "reset" of the conrod clock, as it were? Realistically, I'll probably never put more than 50k more miles on the car, so if failures under 50k mi are rare, then would I be OK...?

I'm an ME but I've got zero experience with sintered metals of this type. And thus have no real idea what's going on when they are undergoing long term deformation. They could be getting softer/weaker with age, in which case I'm not really resetting the clock. They could be constant, in which case I probably AM resetting the clock, or I suppose they could even be relaxing into internal voids in which case maybe they get stiffer (wrt big end deformation).

Thoughts?

Al Seim

Edited by 2000SVTC, 25 March 2011 - 07:38 AM.

[Terry Haines]

I would advise against any m/c on old rods to take os(outer diam) bearings. If you feel you can remove piston pins and pistons then contact me,I have several sets of conrods from engines that were new built at the plant but never fitted to vehicles so they only have engine plant test bed time on them..

[Erbid]

Thanks Terry,

Excellent eye opener. I am wondering whether the deformation over time of the lower rod bearing surface might merit a refit of slightly larger bearings, once the deformation has reached .002" or so. Does the diameter of the bearing surface seem to increase when measured cold on an old rod (one of the "others" in a set with at least one spun bearing)? I'm thinking .002" over may be about right for a preventative maintenance refit bearing on an old PM rod. And since it has compressed/deformed measurably already, perhaps the deformation is complete/nearly complete.

The question being: I is the compacting of the cut surface anything like peening or burnishing, possibly resulting in a more durable, though deformed, surface?

I have an aftermarket baffle set and windage tray. I do not know where the oil level ended up, but it cradled the rods and fit snugly in the pan. But if oil starvation is not the major issue, perhaps I am due for some bearing inspection and refit. I was believing that as the car approached slide/roll on a (needlessly) prolonged high speed right-hander, the oil pickup sucked air. And the additional charge of oil near the pickup may help keep things cooler on the crank.

Erbid

[Terry Haines]

....no 'easy' answer to this.Ford PM rods are not a good choice for an uprated engine.Forged is better then,whithout the 'cracked cap' the stand proud/nip can be measured on a new bearing liner.There are 'tricks' that myself and old sweat engine builders do use to increase the nip but I would not publish them here!..I'd say no to peening/blasting the id of the rod to increase the nip...