Topic: Main bearing clearance. 0.0015” go up a size?

[CB750R]

Hi folks.

I ordered a full set of green shells based on crank and case markings but it’s coming up on .0015 when I plasti gauge the crank. I did it twice, one at min torque value and once again at max torque value, no significant change.

Will going from green to brown shells get me to .0010”?
Is it worth chasing that? Am I splitting hairs at this point?

It’s an 836cc 10.5:1,  Mike R head with a Megacycle 125-60 cam build so it’s going to be pretty alive for a street motor.

[Tracksnblades1]

You on the looser side now. It won’t get any tighter down the road..

[Don R]

 On our 383 Chevrolet race engine we used to run a thousandth smaller shell on one side to get the number we wanted. I've never heard of doing that on these motors but why not? green and brown?
  There, I said it, flame away! L0L!

[Tracksnblades1]

On our 383 Chevrolet race engine we used to run a thousandth smaller shell on one side to get the number we wanted. I've never heard of doing that on these motors but why not? green and brown?
  There, I said it, flame away! L0L!

In 79, the K30, small block 400 3 freeze plug blue paint block came that way from the factory…oil burner on 6&8 @ 15,000 miles…

…it was interesting though because it looked like gm was adjusting the crankshaft align bore more than oil clearance on the mains…it had .001 over and .001 under for all the mains. Effectively moving the crank down tightening the timing chain…the rods however had .001 under with standards all in the caps perhaps oil clearance here…?

Put it back together the same using Delco/Morraine bearings and GM/TRW Ramco rings, GM steel shim head gaskets. Truck stayed local and ran until it rusted down.

Delco bearings have always been able to be purchased by the upper or lowers..Ever since that I paid close attention to the half bearing during disassembling. Noticing the same in the rod bearings of the fuel pinches 262.5, 267, and 305..almost wondering wether the changed their stands or were just using up their junk..by 87 I don’t remember the mixes so much…

Old GM factory production clearances were always tight similar to Hondas .0008- .0018 for a 2.100 journal. Near the same for a 2.450 journal.. The machine shops have dumbed that down to .001 per inch or more where you can hear them knock after an oil change until the air get purged…

Kenny is advertising for sale mixing and matching bearing halves. if I’ve read that right..so great minds must have similar thoughts 😇

[scottly]

Hi folks.

I ordered a full set of green shells based on crank and case markings but it’s coming up on .0015 when I plasti gauge the crank. I did it twice, one at min torque value and once again at max torque value, no significant change.

Is it worth chasing that? Am I splitting hairs at this point?

I would be happy with .0015" on a hi-po motor.

[PeWe]

My K6 got closer to 0.0020".
Found replies about the looser clearance to be ok, more oil flow that can be good with more power.
http://forums.sohc4.net/index.php/topic,69907.0.html

I had used green shells, then brown, finally back to green.
Green looked better after use than brown. Scuff marks, not catastrophic.
Here that setup with slightly used green and new brown.
http://forums.sohc4.net/index.php/topic,155014.0.html

Green went back shortly after when engine had to be opened due to upper case massage for bigger bore.
 
I used assembly lube in all those assemblies so the first startup should have been ok.
Crappy mineral oil 10W-40  as break-in oil the first 1000km might be one reason.

APE Ultra crank with carillo rods.
Now 970cc. Last 2 dyno runs 107 whp. 
That crank setup has done closer to 45.000km, >100whp most of it.

It runs fine. No bad sounds inside. Street use. It is the dyno visits that torture it

My almost stock K2 got the clearances in same range. Also green shells and BBBBB case.

I have a set of new brown shells I found for half price on eBay.
If I should open that engine again and if the shells should look bad.

No Kawasaki vibrations as mentioned in the old thread with Hondaman and Mike Rieck.

APE crank is balanced not only lightened so the engine runs really smooth. Alternator is lightened too.

[newday777]

My K6 got closer to 0.0020".
Found replies about the looser clearance to be ok, more oil flow that can be good with more power.
http://forums.sohc4.net/index.php/topic,69907.0.html

I had used green shells, then brown, finally back to green.
Green looked better after use than brown. Scuff marks, not catastrophic.
Here that setup with slightly used green and new brown.
http://forums.sohc4.net/index.php/topic,155014.0.html

Green went back shortly after when engine had to be opened due to upper case massage for bigger bore.
 
I used assembly lube in all those assemblies so the first startup should have been ok.
Crappy mineral oil 10W-40  as break-in oil the first 1000km might be one reason.

APE Ultra crank with carillo rods.
Now 970cc. Last 2 dyno runs 107 whp. 
That crank setup has done closer to 45.000km, >100whp most of it.

It runs fine. No bad sounds inside. Street use. It is the dyno visits that torture it

My almost stock K2 got the clearances in same range. Also green shells and BBBBB case.

I have a set of new brown shells I found for half price on eBay.
If I should open that engine again and if the shells should look bad.

No Kawasaki vibrations as mentioned in the old thread with Hondaman and Mike Rieck.

APE crank is balanced not only lightened so the engine runs really smooth. Alternator is lightened too.

That Ape crank sure is Purdy! If I come into mega bucks$$$$, I want to build a 970 motor for my brother/Dad's motor with one of those cranks, for the street! Just to give some of the sport bikes at the weekly bike nights a WOW factor of why their sport bikes exist today. I'm collecting the bits along the way......

[CB750R]

Thanks for the replies so far.

I dont think I’ll be mixing/matching sizes guys. Seems I’m in the ‘safe’ side, more reading indicates that id be ‘fine’ as is but if i wanted to chase longer service life i should move up to brown.

The racers, seem to be fine with looser tolerances. But Hondaman seems to advocate shooting for the min range of the spectrum. 

[PeWe]

There is another thread about main bearing clearances where forum member Captain mention 0.0018 as minimum.
That guy is very experienced.
http://forums.sohc4.net/index.php/topic,165595.msg1913259.html#msg1913259

More clearance talk
http://forums.sohc4.net/index.php?topic=101842.0

[CB750R]

There is another thread about main bearing clearances where forum member Captain mention 0.0018 as minimum.
That guy is very experienced.
http://forums.sohc4.net/index.php/topic,165595.msg1913259.html#msg1913259

More clearance talk
http://forums.sohc4.net/index.php?topic=101842.0

Thanks PeWe, appreciate the links. Seeing as i have consistent measurements across the crank and lots of indication that im just fine at .0015 i think i may save the $250 in bearings and stay as is.


I had not seen the page from the manual that says the service limit is .0032, i had interpreted the manuals upper range of .0018" to be the "service limit" so thought the .0015 measured was getting ‘too close to max’

[PeWe]

This forum is stuffed with good info!
Not only how to fix things. How to drain the wallet too!

Important to understand when it sometimes might be a mix of inch and millimeters.

[MRieck]

There is another thread about main bearing clearances where forum member Captain mention 0.0018 as minimum.
That guy is very experienced.
http://forums.sohc4.net/index.php/topic,165595.msg1913259.html#msg1913259

More clearance talk
http://forums.sohc4.net/index.php?topic=101842.0

Sorry for not replying to your email....been busy with this new house stuff. .0015 is very good IMO especially with the heavier oil used in these engines. Good cooling with that clearance. Carrillo's like looser numbers as well...like close to .002.

Thanks PeWe, appreciate the links. Seeing as i have consistent measurements across the crank and lots of indication that im just fine at .0015 i think i may save the $250 in bearings and stay as is.


I had not seen the page from the manual that says the service limit is .0032, i had interpreted the manuals upper range of .0018" to be the "service limit" so thought the .0015 measured was getting ‘too close to max’

[CB750R]

Sorry for not replying to your email....been busy with this new house stuff. .0015 is very good IMO especially with the heavier oil used in these engines. Good cooling with that clearance. Carrillo's like looser numbers as well...like close to .002.

Thanks Mike, I have ordered Yellow shells for the rods based on comparisons from stock rod bore to the Carrillo bore, and indicated journal diameter. Will see how they look when they show up!

[Tracksnblades1]

Hope you got a better read on your plastic gauge than this person did..😳😳

Posted on FaceBook.

Names were changed to protect the innocent, Joe Friday..😁

Wonder aloud what the real clearance is without the lube..?🤔

[CB750R]

Hope you got a better read on your plastic gauge than this person did..😳😳

Posted on FaceBook.

Names were changed to protect the innocent, Joe Friday..😁

Wonder aloud what the real clearance is without the lube..?🤔

You really think a little bit of grease in the center where there’s no bearing material makes a difference?
It could be done a 3rd time.. but a little bit of grease helps keep the plasti gauge in place.

[Don R]

 I just checked one with similar results, .015" mains and I also used a dab of grease in the center to hold the plastigauge in place. It didn't spread between the shells so I'm calling it good.
 Next up, I'll check the rod bearing clearances. The rod bearings are beautiful so I'm hoping for good numbers there also.

[HondaMan]

I am in a K5 just now that had all green bearings and lowish oil pressure (70k miles). I tried the Brown, still too loose, gotta go black. I want them below 0.0015", but they are coming out 0.0018" across the board with the brown. Looks like black will be the last stop before a newer crank.

[Don R]

 How much would you expect black bearings to tighten them up?  I have a set of black ones that came from a Honda shop in Florida after they didn't work in their build. This block was AAAAB and the crank was AAAAA, Unknown miles on this crank though. I want to oil this puppy up and give it a spin test.

[HondaMan]

How much would you expect black bearings to tighten them up?  I have a set of black ones that came from a Honda shop in Florida after they didn't work in their build. This block was AAAAB and the crank was AAAAA, Unknown miles on this crank though. I want to oil this puppy up and give it a spin test.

Since the crank already has miles on it, the Black will fit fine. The 'hidden' truth is that it is impossible to go so tight with the Honda bearings that you would be too tight on the crank or the rods. The issue really only showed up when we'd have to replace a worn crank with a new one, which I've only done once: then it was spot-on with the bearing tables and shell colors - but that was also circa 1972.

When these (750) engines reach about 10k-12k miles they have made almost all the clearance they are going to make for a long time, in my experience. It stays right there, too, if the oil is kept well and not 10w40 in hot climates. The typical crank bearing seems to wear out to about 0.0014-0.0016" [Plastigaged] by the 10k mile mark, and I checked mine at 50k (0.0016" across all) and 121k (0.0018" average, one higher by 0.0002") and then again when I had it apart because of the oil leak at 135k+ in 2013. That last time, 2 of the mains were out to 0.0020", as were the #2-#3 rods, so I downsized them all one color, putting them into the 0.0016"-0.0018" ranges again. Oil pressure has been higher, but I also rebuilt a younger oil pump than mine and used it, which has excellent rotors in it. My old one looked like I ran stones thru it somewhere along the way!

[Tracksnblades1]

I am in a K5 just now that had all green bearings and lowish oil pressure (70k miles). I tried the Brown, still too loose, gotta go black. I want them below 0.0015", but they are coming out 0.0018" across the board with the brown. Looks like black will be the last stop before a newer crank.

Have you ever checked the “plastic gauge” results with a quality bore gauge indicator instead..? Especially when zeroing the bore qauge’s indicator to the locked micrometer reading of the desired crank pin…so one doesn’t have any errors stacking.

Have you ever got “exactly” the same results with plastic gauge…?

I’ve never really use plastic gauge to determine the actual clearance, merely only a double check..
Plastic gauge has always read a little tighter than the actual clearance measured…Our local machine shops have always recommend a quality bore gauge over the plastic gauge.. It hard to get plastic gauge to show out of round, taper, etc, and to keep it perfectly dry as directed…

[PeWe]

And as someone mentioned in one of the previous links, case sealer add some on the clearance too.

[MRieck]

I am in a K5 just now that had all green bearings and lowish oil pressure (70k miles). I tried the Brown, still too loose, gotta go black. I want them below 0.0015", but they are coming out 0.0018" across the board with the brown. Looks like black will be the last stop before a newer crank.

Have you ever checked the “plastic gauge” results with a quality bore gauge indicator instead..? Especially when zeroing the bore qauge’s indicator to the locked micrometer reading of the desired crank pin…so one doesn’t have any errors stacking.

Have you ever got “exactly” the same results with plastic gauge…?

I’ve never really use plastic gauge to determine the actual clearance, merely only a double check..
Plastic gauge has always read a little tighter than the actual clearance measured…Our local machine shops have always recommend a quality bore gauge over the plastic gauge.. It hard to get plastic gauge to show out of round, taper, etc, and to keep it perfectly dry as directed…

👍. Also....you really need a dual ball mic or maybe a blade mic to measure bearing thickness if you want a complete picture.

[HondaMan]

I am in a K5 just now that had all green bearings and lowish oil pressure (70k miles). I tried the Brown, still too loose, gotta go black. I want them below 0.0015", but they are coming out 0.0018" across the board with the brown. Looks like black will be the last stop before a newer crank.

Have you ever checked the “plastic gauge” results with a quality bore gauge indicator instead..? Especially when zeroing the bore qauge’s indicator to the locked micrometer reading of the desired crank pin…so one doesn’t have any errors stacking.

Have you ever got “exactly” the same results with plastic gauge…?

I’ve never really use plastic gauge to determine the actual clearance, merely only a double check..
Plastic gauge has always read a little tighter than the actual clearance measured…Our local machine shops have always recommend a quality bore gauge over the plastic gauge.. It hard to get plastic gauge to show out of round, taper, etc, and to keep it perfectly dry as directed…

👍. Also....you really need a dual ball mic or maybe a blade mic to measure bearing thickness if you want a complete picture.

All so true!
It takes practice to 'read' Plastigage and understand what it is really telling you.

[HondaMan]

How much would you expect black bearings to tighten them up?  I have a set of black ones that came from a Honda shop in Florida after they didn't work in their build. This block was AAAAB and the crank was AAAAA, Unknown miles on this crank though. I want to oil this puppy up and give it a spin test.

The step-down size, all else being 'equal', is about 0.0004" from one to the next size down, when read with Plastigage on the same bearing.

[CB750R]

Well i did check them dry, and it seems pretty dam similar to me. Im going to run with what i have.