Yet another rod bearing question...

[rm97]

Hello,

After searching through the forum I had gathered that Clevite bearings fit for a 1988 Mazda 323 would be a suitable substitute for the stock Yamaha big end bearings. I got the bearings, the OD, ID, and thickness all seem to be about identical to my old bearings (I have not yet checked oil clearance). All that seems great, but my concern comes from the fact that the stock bearings are 1.8mm wider than the new ones. This not only reduces surface area, but also causes the bearings to be positioned off-center & off-set to one another. The Mazda bearing's retaining tab is also slightly wider than the stock bearing's so it must be filed down to fit. Finally, the Mazda bearings are not drilled to allow oil to exit through the passage in the connecting rod.

Is there anything to be concerned about here? Did I end up with the wrong bearings? Should I drill an oil hole to mach the one on the con-rod? What negative affects (if any) will narrower bearings create? Can I go ahead and file down the width of the retaining tab (filed surface will not be a bearing surface)? I apologize if I could not find a previous post asking the same question, please post a link if such a thread exists! Pictures can be added if my description does not suffice.

Thanks in advance,

Rory

[Rick G]

Don Minor has used them and is the person who told me about it. I don't believe this will cause a problem . How ever I'll try calling Don and ask him. I'll report back on what he tells me.
I called Don and he  told me a bit about the Mazda bearings. They are 4 layers as opposed to the Visions one .  They work fine !!
The reason the  Vision blows rod bearings is that the clutch debris builds up and plugs the pickup screen! If your oil light pulses at idle , the screen is plugged , CLEAN IT NOW!Clean it anyway!!
Don laps the oil pump to remove all the wear marks  and tighten it up. He packs the oil relief plunger as well.
His email is minordon@yahoo.com

[rm97]

Thanks for the help! I didn't think it would be an issue, but I want to be sure I do all of this right the first time. I did clean out my oil pump screen, and I was amazed at all the metal chips, bugs, and strings of yamabond #4 came out of it. Are you saying he packs the oil relief with grease? All I have done with mine so far is inspecting it, cleaning it, and replacing the o-ring & cotter pin.

Thanks again,

Rory

[Rick G]

Don  disassembles the pressure relief valve and puts a small washer in it, to increase spring pressure. I did it many years ago on my '54 ford six, by stretching the spring, or adding a washer.

[rm97]

Okay thanks for the clarification, I'll be sure to give it a try on my vision!

[Rikugun]

rm97, thanks for posting your observations. I don't think I've seen such detailed comments regarding the Mazda bearings replacements. Unless there was and I missed it... :-[  Good stuff anyways!  :)

Are the Mazda bearings you sourced standard or oversize?  I can understand your concern over the size/offset issue as it relates to loading and area but the oiling hole seems just as important, no? Are there any other oil distribution features - grooves or channels for instance?  Rick gave some goods tips on oiling too BTW to ensure good pump pressure.

So if I'm understanding you, due to the smaller size and offset, the two bearing shells only provide a small band of contiguously supported contact around the journal? I can't help but wonder if it will be as long lived as the originals.

[jasonm.]

Don  disassembles the pressure relief valve and puts a small washer in it, to increase spring pressure. I did it many years ago on my '54 ford six, by stretching the spring, or adding a washer.

I will explain the relief valve in the side case...It is to leak oil back to the crankcase when pressure exceeds 70 psi Prior to reaching any moving parts. You want this to work @70psi...not higher. Reason being if pressure is too high in the oil gallery, there is a relief built into the OIL FILTER. And should this relief "pop" ...you will be sending UNFILTERED oil into the crankshaft and rod bearings. This could include metal bits and such. And this WILL cause a bearing failure.  People need to understand this design... I cannot comment much on the Mazda bearings..except to say , if does not have the same phyisical make up...oil holes, etc.... positive results are not likely to last long.

[Rikugun]

Yikes  :o  I don't like the sounds of that one bit :-\ :'(  Unfiltered oil you say!?

[rm97]

My bearings are standard. The front rod bearing was severely worn, and the rear bearing seemed to be bent, causing the rod to stick instead of spinning freely around the journal. Luckily I caught the problem quickly and my crank journal received no significant damage.

The oiling passage is an oil relief passage, not an oil supply passage. As I see it, rendering such a passage useless would increase the oil pressure in that area and allow the rod bearing to float on the layer of oil, instead of rubbing on the crank. I'm not sure what negative affects removing that passage has on the system... someone more knowledgeable would have to answer that question. There are no oil distribution passages on the bearing.

The small size and off-set is what had me worried the most, and is what led me to post this thread. Unfortunately, since I can't find stock bearings these seem to be the best known option aside from custom built ones. I hope that the increase in bearing quality, and possible increase in oil pressure will lead to success.

I guess I will scratch the oil relief modification idea. Maybe the relief valve spring becomes less stiff over the years and needs a bit of help?

[Rick G]

Don relates that he has 40,000 miles on his Mazda rod bearings, He has used this option more than once. He (like  me) is very hard on his bikes, expecting maximum performance and running the shite out of them.
The reason for the shim on the oil plunger is to restore a 30 year old  spring to something near new specs. As I said its an old trick , which was old when I was young.
There was a post years back , from a Visionary in one of the Scandinavian countries , who used Mazda rod bearings , to rebuild his XZ.  I believe he reported success.
As to the quality of the stock bearings, as far a I'm concerned , there junk, anything would be an improvement.

Here is a correction for Don Minors email address minordon@yahoo,com

[rm97]

Thanks for the input everyone! I'll be checking oil clearance on the new bearings as soon as I can get my hands on some moly grease.  I will also look through my shop manual to see if they give any specs on the kg/mm rating of the oil valve spring.

[rm97]

I finally got some moly-grease so I was able to put the rods back on the crank. I greased up the bolts, tightened the rods with the plasti-guage in place, removed the rods, and saw that the clearance was well within spec. I then removed the plasti-guage, re-greased the bolts, oiled up the crank and bearings, and torqued the rods back on 9ft-lbs at a time until I reached 27. I was happy to see that everything was going smoothly, but when I went to see how smoothly the rods spun on the crank I was very disappointed. The rods were almost stuck, I could get both rods to spin, but not easily. Thinking that this didn't seem right, I redid the entire procedure and ended up with the same results. Is it okay for the rods to not spin easily like this? Will this no longer be an issue once pressurized oil is running through the system? If not, does anyone have any ideas as to what is wrong, and how I can fix it? The crank was in good shape (and within spec), but I did replace the connecting rods. Considering clearance is within spec I wouldn't think this is my problem.

Thanks,

Rory

[motoracer8]

Are the rod journals round? Did you measure them? Do the rods have enough side clearance with the offset Mazda bearings.

Try one rod at a time on the crank.  Don't stretch the rod bolts too many times, they can break in use.

[rm97]

I will measure the rod journal, but I do know that the crank journal is round. The rods have plenty of side clearance, the new bearings don't affect this. I double and triple checked that the rod caps were on the right rods/not turned 180*.

Just checked, con-rod journals are indeed round. I also re-checked the crank, which is still round :D

[fret not]

According to Craig at Hanson Racing Technology in Chico, CA the crank journal needs to be ground about .001".  Since you checked with plastigauge and your clearances are within spec I don't know what else to suggest.  If you have clearance you have clearance. 

Sometimes the big ends of the rods become slightly egg shaped and need to be re-sized.  Precision grinding of the mating surfaces of the rod caps to close up the hole, and then precision reaming of the big end of the rod to make the hole round again.  I read about this on the Clevite website some time ago, hope I got it right.

[rm97]

I think I will measure bearing clearance again with the plastiguage. I have a feeling I might be better off getting the crank ground, and purchasing oversize bearings. At the very least I will probably have a machinist measure all the parts using some real precision tools. Any other suggestions are welcome.

[Rikugun]

I think I will measure bearing clearance again with the plastiguage.

that sounds like a good first step. try and measure 90 degrees to where you measured it last and see where it is.

I've never had one of these apart so bear with me....  Did you say there was a hole in the rod that was covered by the Mazda shell? Did you end up drilling a matching hole in the bearing shell? Does that hole direct oil to the wrist pin?

[rm97]

Yes there is a hole in the rod that is covered by the new bearings. I did not drill a new hole through the bearings. The hole does not lead to the wrist pin, it just squirts out of the side of the rod. Now that you mention it, I might go try to see what that hole could be lubricating, if anything. At first I thought it was just an oil relief, but maybe it sprays oil on the cylinder walls.

[rm97]

Also, on the topic of the pressure relief valve... Looking through my Yamaha shop manual, it says that the oil relief valve opens at about 57psi, while the oil filter bypass valve opens at about 14psi. In other words there is really no point in increasing the relief valve's spring pressure, as the oil filter bypass will open up long before the relief valve does.

EDIT: After doing some more measuring and making some careful observations, it seems that the new bearings have a slightly larger OD than the rod ends. This causes the the bearings to pinch the crank journal right where the con-rod and con-rod cap meet. I think I will just take the crank and rods to the local engine machinist and see what kind of advice I get. I could try modifying the bearings a bit, but I don't think that is worth the risk.

[Rikugun]

Now that you mention it, I might go try to see what that hole could be lubricating, if anything. At first I thought it was just an oil relief, but maybe it sprays oil on the cylinder walls.

I wondered if it was angled to shoot oil towards the underside of the piston. Are there small oiling holes through the piston skirt in the oil control ring lands?