Topic: 750 main bearing clearance, a compendium of information. Re-run.

[scottly]

A B crank with a B main calls for a green bearing, but, due the the range in B sizes will result in a clearance from .025-.046mm. The yellow bearings are the "loosest" next to the green, and have as much as .008mm, or .003" more clearance, if I did the math right.(It's late ) You might try yellows in the two left side bearings?

more like 0.00011812. Your getting into the micron range when you get three places past decimal in MM
toolmaker just leaked out
sorry
Jim

Looks like I missed a decimal point, Jim. I should have said .0003".

[scottly]

  I got back into the shop today, put the dial indicator on the crank and don't find a wobble on the ends either.

Was this with only the outside shells installed? Try installing the inner shell on the tight end, with no outer shell, and check the run-out on the outside journal.

[754]

Hey, ran inti engine shop guy tonite, he says they  bump the cranks back to true, fairly often.
 Not bad bent ones just out a few thou.

[Don R]

http://www.cyclexchange.net/Cranshfts%20and%20Connecting%20Rods%20Page.htm

 Read the Words of Wisdom from a Honda Wrench, it's most of the way down the page. Interesting for sure, I'm not saying it's correct, but is what I'm experiencing. L0L!

[754]

I was hinking that earlier, you could safety wire if you were worried .

[Terry in Australia]

I've just been using greens since one of the more astute members here suggested it years ago, and so far, no issues. I often wonder though, do we replace them because they're worn out, or just because we think it's the right thing to do? The same goes for cam chains, primary chains, gearbox bearings etc. Most of the ones I've replaced looked pretty good, but of course I'd bought the parts before I stripped the engines down, so the only real justification for replacing them was that I didn't want to think I'd wasted my money.

The F engine that I'm installing in my K2 "Bitsa" has never been apart, not even for a clutch, so I'm not going to pull it apart until I hear it running. If it sounds Ok then I'll just ride it, if not, well it will have only cost me the time it took to pull the engine back out again. I don't know if I'm getting wiser with age, or just lousier..........  

[kmb69]

http://www.cyclexchange.net/Cranshfts%20and%20Connecting%20Rods%20Page.htm

 Read the Words of Wisdom from a Honda Wrench, it's most of the way down the page. Interesting for sure, I'm not saying it's correct, but is what I'm experiencing. L0L!

It may indeed be a "makeshift" fix that will let you get by short of solving the real problem. Assuming your crankshaft is not bent and the bearings are not damaged, this issue may indicate that the cases are yielding prematurely to their designed intent. I would bet that they torqued properly and spun freely when assembled at the factory. I'm guessing that heating/cooling cycles and/or stress/stress relieving have caused the cast cases to fatigue and deform over time. It may be ok to run looser torque values for street motors or even mild hop ups. Personally, I would not be confident with that solution on a racing motor making serious power. Since your crank indicates true, you might try torqueing it in another set of cases to see if the results are different. That might isolate the problem to either the crank or the cases IMHO.

[BPellerine]

I've just been using greens since one of the more astute members here suggested it years ago, and so far, no issues. I often wonder though, do we replace them because they're worn out, or just because we think it's the right thing to do? The same goes for cam chains, primary chains, gearbox bearings etc. Most of the ones I've replaced looked pretty good, but of course I'd bought the parts before I stripped the engines down, so the only real justification for replacing them was that I didn't want to think I'd wasted my money.

The F engine that I'm installing in my K2 "Bitsa" has never been apart, not even for a clutch, so I'm not going to pull it apart until I hear it running. If it sounds Ok then I'll just ride it, if not, well it will have only cost me the time it took to pull the engine back out again. I don't know if I'm getting wiser with age, or just lousier..........

terry,I have always thought that a part was either good or bad,not much wiggle room there,so I measure the old parts and inspect them,rather than just replace everything,for a street bike,sometimes a good used part is better than a new repop,I was taught that many years ago.bill

[NitroHunter]

I think if you have a good pressure oil pump and decent weight oil, looser bearing clearance is desirable. Don you know the toys I play with nowadays, our norm is .004" and we scotchbrite the bearings every lap. I've read RC Sr. had that much in the Sorcerer and he never had oils like we do now.

[754]

Robbie, how many minutes before main and rod bearing changes ? Or inspection.

[Don R]

http://forums.sohc4.net/index.php/topic,8965.25.html

 More bearing talk. I'm committed to yellows and more checking but am enjoying the learning process.

[Don R]

I think if you have a good pressure oil pump and decent weight oil, looser bearing clearance is desirable. Don you know the toys I play with nowadays, our norm is .004" and we scotchbrite the bearings every lap. I've read RC Sr. had that much in the Sorcerer and he never had oils like we do now.

 True, in the thread above it's said RC suggested yellow mains and green rods. I've been under a hot alky motor and helped check mains. What an experience, would love to do it again but not every week. Some dripping 80wt makes your hair stay put, but really smears your safety glasses. That's why I run Super Comp, that said the rear end in that thing is eating up all my dragbike money.

[Jerry Rxman Griffin aka MuthaF'er]

Don, I probably have a bunch of yellows if you need a decent deal.

[Don R]

Don, I probably have a bunch of yellows if you need a decent deal.

 That would be awesome Jerry, I almost pulled the trigger a few minutes ago but thought I'd re-read here first. I still have an old phone number left over from the Honda world tour if you want to text or just PM here.

[Don R]

 I did try an alleged set of greens on the two offending mains with no change. I'll try the yellows and plastigauge several spots on each one.

[Bill/BentON Racing]

Yellows or different cases, g'luck

[Captain]

 I don't want rain on your parade and are only trying to give you a heads up on what works.
The difference in clearances between Yellow and Green is not enough to come anywhere near solving your problem.
1/ If you crank is straight then your cases aren't and that's end of story. Replace with cases that are as anything less you will live to regret.
2/ in these small journal size engines with the oil system delivery and pump capacity and speed .004" clearance is NOT recommended. You will struggle with oil pressure at low RPM and the volume through the bearings at speed will result in an inconsistent hydrodynamic oil wedge. In other words you will not 100% establish oil separation between the crank and bearings.
 
For a SOHC  (& DOHC) Honda 4  69 thru 83  NA on gasoline, steel or Titanium Rod the clearance is .0018"
Absolute max is .0025"

 Captain

[Don R]

 Humor me, I concede something here makes no sense but sometimes the journey is as much fun as the destination. I have .001 now according to plastigauge but am not positive what bearings are in it now. As far as I know they may be black. I plan to proceed one step at a time. If I find no joy, there are other cases and other engines I can build.

 With any luck I may learn something or at least gather bearing and crank info in one place so others may find it easier. I'm already confident enough to split and replace the cases by myself. Previously, I thought I needed help.

  The .004 Nitrohunter is referring to is on another beast all together. (Big inch blown hemi) I think he is making a point that .001 is tight for a race engine, not recommending .004 as a clearance on this engine. I do appreciate all input thanks to everyone that posted opinions and facts. The story on CycleX just confirms I'm not the only person to ever come across this.

 

[dragracer]

Keep it going Don. I think we're all learning something from you and those who are offering their experiences in bearing clearance issues.

[kmb69]

.....
For a SOHC  (& DOHC) Honda 4  69 thru 83  NA on gasoline, steel or Titanium Rod the clearance is .0018"
Absolute max is .0025"

 Captain

If there's anyone that can tell you with absolute certainty, it's Brent.
He's making more NA horsepower with a DOHC 1100 than anybody on the planet. Pretty sure he's close to 200 HP.

[Don R]

 Point taken, thanks Captain.

[Jerry Rxman Griffin aka MuthaF'er]

We just have to be confident we don't mix metric and standard measurements and decimal points. I personally prefer to use metric measurements on metric bikes.

[kmb69]

We just have to be confident we don't mix metric and standard measurements and decimal points. I personally prefer to use metric measurements on metric bikes.

Brent's numbers are in inches.

[Jerry Rxman Griffin aka MuthaF'er]

Understood, just basic principles we need to be aware of.

[Captain]

  I wrote .0018" which is clearly imperial.  If I was stating a metric size it would be followed by mm.

 Now getting back to the clearance question again........   .001" is only liveable in in a low load and low RPM situation. (an engine that is being babied)  The reason for this is that the volume of oil that the clearances allow through is restricted and once load and RPM are introduced additional heat is generated and this volume now is very much borderline for carrying away this additional heat. When this happens you lose control of the cooling management then it compounds itself and spirals into more heat less cooling and so on until the maximums are exceeded.  At that point you burn the bearings and if you keep going will either seize or break a con rod bolt or the rod itself.

 Captain