why blacktops run bearings.....

[Mr Revhead]

i'v talked about this with several ppl over the years. but never put it up here for discussion

blacktop 4ages have a habit of running bearings rather more often than the other versions

http://kinloud.blakjak.net/images/Toysp ... ds3web.jpg

thanks to kinloud for the pic, but see the notch in the side of the blacktop rod?
i think that allows more oil past it than the holes in the other versions of the 4age rod. so when you have a high rev loss of pressure that say a smallport or silvertop may survive, the blacktop doesnt and runs number 4 bearing

what does toyspeed reckon?

[strx7]

Late Bigport/Early Small port rod in pic, is that the same as the AE92 4AGZE rod? Looks the same as the ones i have seen

[Dell'Orto]

Sure is.

[thegreatestben]

Noticed that notch when looking at the pic earlier tonight.
Makes me count me my blessings after seeing alot of 8500rpm last weekend

[Distrb]

i agree, but a run bearing isn't always the final result

[Bling]

I can't comment on race related 'breakages' but I think as long as you keep the oil topped up you won't have a problem on the road.

Although in saying that i've been caught out a couple times with no oil on the dipstick... so it should have gone bang by now but still loves to hit the high 7k range

[fivebob]

see the notch in the side of the blacktop rod?
i think that allows more oil past it than the holes in the other versions of the 4age rod.

Why would that matter?

Oil is pressure feed through the crankshaft. As long as there is the same clearance and the bearings are the same size, then the oiling should be the same.

[KinLoud]

I don't "know" so here is my opinion...
- I feel it's unlikely that Toyota would do something to make a part more unreliable.
- It's pretty hard to get a good statistical number of blacktop bearing failures vs other 4age failures. So I can't comment on blacktops being worse than others as far as bearings go.

BUT
I would say my gut feeling about 4age rod failures might be correct:
- blacktop rods fail/break sometimes
- other 4age rods don't break

Here is a repost from my conrod thread in tech faq.

All you conrod geeks - read this article that discusses powder forged rods vs drop forged rods
http://www.metal-powder.net/business/ar ... jun05.html
Powder forged rods are better in many aspects.
An interesting part of this document relates to failure of powder forged rods:

"Powder-forged rods typically failed at or near the minimum cross-section of the I-beam, where both surface and sub-surface crack-initiation sites were observed. Drop-forged connecting rods were found to fail in a less consistent fashion, which scanning electron microscopy revealed to be related to defects such as oxides, folds and microcracks. This could explain the much larger scatter of fatigue strength values exhibited by the drop-forged rods."

Sounds like the Blacktop rods could be produced using the powder forged method as this could explain why they all tend to fail in the same place??

Ken
Auck
021 408 863

[Mr Revhead]

see the notch in the side of the blacktop rod?
i think that allows more oil past it than the holes in the other versions of the 4age rod.

Why would that matter?

Oil is pressure feed through the crankshaft. As long as there is the same clearance and the bearings are the same size, then the oiling should be the same.

yep, but my theory is that notch allows more oil through it, therefore less resistance to the oil passing through there which decreases the pressure in the journal. and when that happens with an instance of lower than normal pressure, say surge from hi rpm corner or low sump volume (coz lets face it, theres bugger all in there) they are more susciptible to a run bearing.
also that notch is the only difference in the oil system of the blacktop


i havnt seen many 4age rods just break.... they all seem to be in conjunction with a run number 4 bearing, and in my experience the blacktop is more common. but yeah they do seem to break at that same point, which when you look at it is that bit you mention.

[fivebob]

yep, but my theory is that notch allows more oil through it, therefore less resistance to the oil passing through there which decreases the pressure in the journal.

Again I ask why would that make any difference??? As long as there is oil in the journal the pressure has very little to do with the quality of lubrication and whether or not it runs a bearing.

Oil supply rate is more important than pressure, and rate of supply should be increased with a greater pressure drop across the bearing.

and when that happens with an instance of lower than normal pressure, say surge from hi rpm corner or low sump volume (coz lets face it, theres bugger all in there) they are more susciptible to a run bearing.
also that notch is the only difference in the oil system of the blacktop

Then that is a different to lower pressure causing the problem. It may well be that the higher supply rate, which should be better for the bearing, is more susecptible to oil starvation. Simple solution is to not run low on oil

Do blacktops rev higher than other 4AGs?

[fivebob]

Some interesting reading for you, by the sounds of it (Mass produced 1600cc engine) these tests were probably done on a 4AG
http://www.tytlabs.co.jp/english/review/rev383epdf/e383_044suzuki.pdf

[fivebob]

and from SAE Paper 982439- "Analysis of Con-Rod, Big-End Bearing Lubrication on the Bases of Oil Supply Rate"

The purpose of this study is to analyze con-rod bearing lubrication under reduced oil supply rate conditions. An engine was modified to measure the oil supply rate to a con-rod, big-end bearing. Then the effects of the oil supply rate on bearing temperatures and the contact between ajournal and a bearing were investigated in order to analyze lubrication characteristics. The bearing temperatures increased in accordance with reduced oil supply rate. On the other hand, the contact frequency hardly changed under almost all conditions, but steeply increased near one-third of the standard oil supply rate at the highest speed of 5000 rpm in the experiments. The results show that the reduced oil supply rate decreases the cooling effect but the hydrodynamic lubrication was sufficiently achieved except the above-mentioned severe condition. From the observation using a transparent bearing and a theoretical calculation, the reason of the above results was estimated that the oil flowing out of the bearing ends is sucked again into the bearing near a cavitation region.

[MAGN1T]

All motors spin bearings when they get old, worn and thrashed.

The more bearing clearance, the smaller contact area when the oil film is placed under stress.A worn main bearing reduces the flow to the big end as more will leak out the sides.
A bad tune makes it worse as the pressure (on the bearing) will increase. A bad tune kills other things too.
I've had bearings spin (not on Toyotas) for 2 reasons. 1 was detonation where the bearing was flattend and widened in one part only, that was on an old and worn motor with too much timing. The other was oil starvation and the bearing was wider all the way around when removed. That was just bad maintainence.

Steve

[Mr Revhead]

Fivebob, you make some good points there.... i'll read that lot after work....
blacktops dont rev any higher. and yes when oil levels kept topped up, and under normal use then there isnt a problem with them.

[79rolla]

also doesint the oil pressure reduce the contact arier of the bearing (pushed through the shells) so with the decreased back pressure the oil just takes the easyest rout and escapes insted of holding a bit of pressure around the bearing to reduce the contact surface?

or perhaps not, the guy that told me was old and kinda past his use buy date... all tho he thought he knew everything lol..

[Dell'Orto]

Fivebob, you make some good points there.... i'll read that lot after work....
blacktops dont rev any higher. and yes when oil levels kept topped up, and under normal use then there isnt a problem with them.

Well, yeah they do, other 4AGE's factory redlines are 7200-7500 and BT's are 8000.

[Voyeur]

And dont forget, most blacktops are tuned for 100 octane jap fuel, have higher compression, and when run on lower grades, are more prone to detonation, than any other non JDM 4age, which everybody is comparing them to.

[NZ_AE86]

The're shit!
I would say that low oil levels are to blame for many of them.
I have not seen a blacktop rod that has been any good after a run bearing which could lead me to blame the rods for the bearings that fail?
Maybe early 4age's were no subjected to the same 'pain' as we can subject blacktops to due to the amount of trackdays etc that are available for us to do now?
Failing that I don't know either!?

[thegreatestben]

Am running 15w40 with some moreys stabiliser in my Blacktop currently.
Seems to use it quite well

What should I be running? Maybe some castrol 25w-50 synthetic I was thinking

[Bling]

It will use most oils I run magnatec and mine uses that. It will vary engine by engine, but the harder you push them the more they seem to use.

Drive like a nana and you'll not use much oil if any I go through a bottle between 5k services