Narrow rod bearings?

[JimL]

With no new bearings available worldwide for my CX650/680 engines, I have found correct size/thickness in a narrower bearing (small 1500cc car application), and I can notch the stock forged rods to accept them.  My "best" used rod bearings are baking the oil behind the shells within a couple passes, so my old bearings are no longer safe.

I know the NASCAR guys run narrow bearings, but I only have about 45 psi oil pressure available in these engines.

thoughts, advice, ideas?

Thanks for any experience you can share.

JimL

[tallguy]

This may be a real longshot, but here goes anyway:

I'm not familiar with your vehicle or what class you plan to run in,
but if it's allowed within the rules, have you considered some kind
of "supplemental" lubrication system that includes a pressurized
(more than 45 psi) oil tank? 

How about enlarging some of the oil passages that specifically feed
the bearings in question?

Good luck, whatever you decide to do. 

[fordboy628]

With no new bearings available worldwide for my CX650/680 engines, I have found correct size/thickness in a narrower bearing (small 1500cc car application), and I can notch the stock forged rods to accept them.  My "best" used rod bearings are baking the oil behind the shells within a couple passes, so my old bearings are no longer safe.

I know the NASCAR guys run narrow bearings, but I only have about 45 psi oil pressure available in these engines.

thoughts, advice, ideas?

Thanks for any experience you can share.

JimL

Jim,

Don't ask me how I know this, but Nascar engines run narrowed AND smaller diameter bearings.   Their dry sump systems supply 55 psi.

If your setup is "baking" the oil, your oil temps are probably too hot.   Do you monitor/record oil temps?   Are you using a synthetic oil after the "break-in" period?   Can you increase the oil volume to extract heat from the engine?   With an additional tank?    Or other ways?    Can you "improve" (increase) oil flow through the engine?    Do you use or can you fit an oil cooler?   Can you increase the oil pressure a bit?   Etc, etc.

What is the % decrease in bearing area?   Single digit, I'd say OK give it a go, IF, your current bearing wear is "reasonable".    If your current bearing wear is "marginal" or the % decrease in area is double digit, I would be very careful and wary.

Also, a higher load capacity bearing material, can have its' area reduced "somewhat", and still carry the original load.   I have no idea about your current setup, so more info please.

I would also "dowel pin" the bearings, ala drag racing practice.   The shells can't spin in a bearing failure.   Won't help the rod or bearing, but it might save the crank.    Spun, melted bearings are always a disaster . . . . . .

Hope this helps.
 
Fordboy

[generatorshovel]

JimL, I feel your pain finding OEM Honda bearing shells, but they are "out there"

http://www.partzilla.com/parts/detail/honda/HP-13220-ME2-003.html

The link below will show part numbers, but cmsl have nil stock, the link above was found by cut/paste/search method, laland can be your friend

http://www.cmsnl.com/honda-cx650ed-canada_model17071/brgf-connrod_13220me2003/#.VYVgXEYmkp1

Tiny

[RichFox]

On my Plymouth with the Crower rods I used two SBC bearings. I made a fixture to chuck them in the lathe and narrowed them about 1/3 width each. Which together was the stock '32 Plymouth width. So if your replacement bearings are significantly narrower than stock, perhaps you should consider two inserts cut to width.

[JimL]

Thanks for all the answers, gentlemen.

Notes:
- the engine is a single pin, 80 degree V-twin with the rods extra wide to run side-by-side (cylinders are offset)
- dont know the oil temp but I can lay bare hands on the crankcase after a run and not get burned.
- the engine oil looks like new after the event.  Just the back of the bearings has turned black which tells me they are loose in the rods.
- plastigauge tells me they are too loose, also.
- the bearings I found are for a Toyota Tercel engine, not as narrow as the NASCAR bearngs I have seen, but about 3 mm narrower than the very wide stock bearings. 
- thanks for the note about part suppliers.  I have contacted them in the past....no parts actually remaining.  The last parts they had were the thinnest shells (largest clearance) in the select fit range.  I dont need more clearance because I am using an extra 2000 rpm above the original redline.

One thing I cant figure out is the rod-to-rod "side contact.  I dont see any sign of wear, but I am not sure what narrowing the bearings will do with this arrangement.

I made a primary case with a window to watch oil relief, a few years back.  I am in relief pressure at 4000 rpm (45 psi).  I see by the reply that I should look at shimming the relief valve.

Fordboy- years ago I made a sensor/relay "logic system" (no transistors or memory circuits was a requirement) to prevent starter engagement until oil preheat temp exceeded 145 degrees (for a NASCAR engine used in a street application).  Perhaps I should be preheating my oil before a run?

This is quite a puzzle, and I am down to my last engine.  Thanks for the replies and detective work.

JimL

[RichFox]

So that is about 1/8 inch width you are giving up? i think i would just run it. But that's me guessing about your engine.

[fordboy628]

Thanks for all the answers, gentlemen.

Notes:
- the engine is a single pin, 80 degree V-twin with the rods extra wide to run side-by-side (cylinders are offset)
- dont know the oil temp but I can lay bare hands on the crankcase after a run and not get burned.
- the engine oil looks like new after the event.  Just the back of the bearings has turned black which tells me they are loose in the rods.
- plastigauge tells me they are too loose, also.   You need to check the big end sizes.
- the bearings I found are for a Toyota Tercel engine, not as narrow as the NASCAR bearngs I have seen, but about 3 mm narrower than the very wide stock bearings.  % area lost for upper shell?
- thanks for the note about part suppliers.  I have contacted them in the past....no parts actually remaining.  The last parts they had were the thinnest shells (largest clearance) in the select fit range.  I dont need more clearance because I am using an extra 2000 rpm above the original redline.

One thing I cant figure out is the rod-to-rod "side contact.  I dont see any sign of wear, but I am not sure what narrowing the bearings will do with this arrangement.   How much total clearance is there?   Should be "about" .018" min.  (.006" per gap)

I made a primary case with a window to watch oil relief, a few years back.  I am in relief pressure at 4000 rpm (45 psi).  I see by the reply that I should look at shimming the relief valve.

Fordboy- years ago I made a sensor/relay "logic system" (no transistors or memory circuits was a requirement) to prevent starter engagement until oil preheat temp exceeded 145 degrees (for a NASCAR engine used in a street application).  Perhaps I should be preheating my oil before a run?   Definitely!

This is quite a puzzle, and I am down to my last engine.  Thanks for the replies and detective work.

JimL

Preheating the fluids was one of the changes to the M/Midget for the '14 season.   Can't say it definitely helped because I don't have any data to confirm it.   BUT, the data I do have is that the car was definitively faster, as in new class record and new personal best run for Chris.

This is part of something I posted on MM's build diary, after he set the new record:

5)  Drag reduction gains.
     A)  Lower viscosity fluids; engine, trans, diff.
     B)  Higher fluid temps.  Used magnetic heaters to preheat engine oil and diff fluid.
     C)  Brake drag reduction.  Well, no more front brakes!!   And backed off on the rears.
     D)  Trick wheel bearing grease.   Some NASA developed stuff used for racing bicycles.
     E)  Change front toe-in from 1/8" in, to zero.
     F)  Change tire pressure from 50 psig to 70 psig.  Seemed to help rolling resistance, but again,?
     G)  On a totally subjective note, 'the car' has become quite easy to push.   Once it's rolling, one person can keep it going with a mere two fingers . . . .

All the "little things" matter, AND, no big surprise, they add up.

Are the big ends of your con rods at the proper housing bore size?    If not, (say too big . . .) you will have a heck of a time keeping bearings in it.    Inspect the back of the bearings and the ID of the housing bore for "fretting".   Use a magnifying glass, 5x to 10x.    You might be surprised.  If you have fretting, you need more "crush" on the bearing inserts.

 
Fordboy

[Dynoroom]

Jim, it is not uncommon to run narrow bearings, I do it all the time. Of course it depends on crank loads, surface finish,  & speeds etc. but it can most likely be done in your case without issue. .060 to .125 depending on the original width is not a problem.

I always look at the backside of the bearings on engine tear down, brown or black indicates heat is not being removed from the bearing. Sometimes this is due to the lack of side clearance or low oil psi, or maybe oil viscosity being to low for the pulse loads. Now if you see fretting on the back side you will want to look at the bearing crush. Most rod manufactures have about +/- .0008 to .001 tolerance on bearing crush. Put your rod together w/o a bearing and measure the i.d. checking for any out of round. If the rod is on the large side of the manufactures specs it can be resized to hold the bearing shells tighter. This will however also tighten the bearing clearance so make sure you have enough clearance before going through this process.  
Another thing I've seen folks do (that I don't agree with) is putting the bearings in with oil on the back side of the bearing and in the rod housing. I don't do this. In fact I wipe the back of the bearings and the in inside of the rod bore with lacquer thinner just before assembly. Any oil behind the bearing shell lessens its ability to transfer heat out of the rod.

YMMV just what I do...

I added a picture of a fixture I made to narrow bearings (I think I have a better picture of the thing at work, sorry)

[saltwheels262]

you can get stick on 120 volt heaters that are flat and flexible from McMaster Carr.

they are different sizes and wattage. they are fairly inexpensive.

Franey

[RichFox]

It is my belief that rod to rod clearance should be wide enough to allow enough oil flow to carry away the heat caused by it's friction as the crank turns. Giving up some oil pressure for flow seems to be a good trade off. As long as your oil system can keep up. If the oil is trapped for to long it seems as though the heat would build up. have you increased your side clearances from stock?

[JimL]

Put together, this has been a really fine education for me.

New bearings is absolutely necessary, and the Tercel bearings are my only choice.  I can raise pressure, and I can preheat the oil so these are part of the agenda.  I need to tear back down, again, because I have added another .100 valve lift and I need to put caps on the valve stem tips on this pushrod engine.

While the heads are off, I can renotch the rods for the different bearings.  These are odd ducks to pull the pistons out of.  The block is cast with two "thin spots" in the bottom of the internal crankcase (they run as a semi-dry sump with the crankshaft almost enclosed and several inches above the oil level).  During manufacture, a pair of holes are knocked in the bottom of the internal crankcase to access the rod nuts and caps.  Every one is different and some of the holes are dangerously sharp and ragged in these thin wall, die cast blocks.  The access to those holes is from the side, with only enough room for one hand to reach into.

Getting the pistons out is really a nasty job; these were never meant to be rebuilt or reused.  In some cases it is necessary to drill and tap the piston crown to yank it out with a slide hammer.  It makes a fellow think twice each time an engine has to come apart.

Thank you, everyone...trying to make it to 2016 Speedweek.  Good luck at 2015, go fast, break a record!

JimL

[wobblywalrus]

Jim, what are the clearances between the big end journals and the shells with your Tercel bearing set up?  How does it compare with production clearances and the ones you usually use?

[jacksoni]

My thought is that if the bearing is getting hot as evidence of the cooking you describe, you need more oil flow at the bearing, not necessarily achieved with more pressure. Side clearances of the rods either single or paired are generally much larger than the bearing clearances ( 0.010" vs 0.002" for instance)  and do not control flow. See piston guided rods for instance. Has no effect on oil pressure if properly done. What are your bearing clearances and what are the factory recommended- which may be too tight- see below thoughts? Plastigage is not the way to find out. Measure them and machine, grind, pick bearings ( hard in your setting with few available parts I understand) and set them correctly. Many stock clearances are small and scary in a race setting.( Have seen recommendations in the less than 0.001" range up to 0.0015". Not near enough in a leaned on race motor- IMO. I regularly see recommendations for rods in the 0.0025" and mains in the 0.003" range) Up to a point, going larger is not a problem and may fix your issue. Obviously opening bearing clearances may affect oil pressure so that system must be able to handle the flow. Narrower bearings may help power with less friction but I do not believe will fix your heat issue. A too small clearance with a large bearing is still too small with a narrow one. The other suggestions by Dynoroom and Fordboy of course add to this and they have far more real world experience so take my thoughts with some salt but I think what I have suggested may help (that is open the bearing clearance, side clearance is not the issue)

[wobblywalrus]

My Triumph is set up within the range of 0.003 to 0.004 inch rod big end clearance, as recommended by an LSR tuner familiar with the engine.  Another guy told me "run 'em loose and change 'em often" so I check and change them annually during the off season.  I have had some bearing shell problems that I attribute to use of an oil additive that I should have avoided.  There never have been any signs of overheating.