Topic: CB750 crank: Plastigauge really needed? Honda case marks + journals measured.

[PeWe]

I'm a liitle bit lazy and plan a quick fix of my engine. Fresh APE crank to get in
Case has letters BBBBB, all crank journals have same sizes, 35.980 - 35.985mm. Measured today with micrometer on both ends of each journal.

Green shells according to Honda manual. Green is mounted today. Have only 5000kms and must be OK. I'll see if something has happened when open the cases.
Plastigauge not needed, right? Or can case sizes differ from marked BBBBB?

I had friends back in the early 80's that went on green shells as a std procedure without measure anything.

[mystic_1]

With a fresh crank you could probably get away with skipping it, but it would be super annoying to me personally to not know.

mystic_1

[PeWe]

Yes, maybe for me too when I have plastigauge home.
I ask here to check others experience. Maybe always correct.
Plastigauge used when a good and expensive micrometer is not available.
I borrowed one over the weekend from my jobs mechanical lab.

[mystic_1]

Oh yeah thats the first thing i noticed is you were using the right tool for the job.  Some might argue that measuring with micrometers and telescoping gauges is better than plastigauge.

IMHO the crankcase markings are unlikely to be off, so if everything's measuring up well than I so go for it.

mystic_1

[Artfrombama]

Both my rod and main journals were smaller than marked.
$2.60 for a stick of Plastigauge, ain't gonna hurt anything then you'll know for sure.

[PeWe]

Update:
I did the practical verification with new crank and found that the clearances are on the loose side.
I got around 0.050mm / 0.0020".
Max clearance according to the Honda manual is 0.046mm /0.0018".

Green shells in which corresponds well with the crank and stamped cases. They green shells have max 6000kms. Old crank is slightly slimmer.
"Case has letters BBBBB, all crank journals have same sizes, 35.980 - 35.985mm"

The cases must have become sloppier after being banged hard during >100.000kms 
I'll put brown shells in and enter the better zone of clearance.
Or, is black the better choice?

Edit: An old thread from the experienced guys... http://forums.sohc4.net/index.php/topic,69907.0.html
Back in the days I also heard use green shells and forget the rest. An old banged case can be an excuse for tighten up the shells though.

[Jerry Rxman Griffin aka MuthaF'er]

Mine was similar to yours. I was not so much concerned about the numbers as I was the oil pressure. I ended up going with the black in 4 of the 5.

[PeWe]

I have read threads where some guys accept 0.002"/0.050mm. I'll feel better if using clearances within max and ensure oil pressure too.
Each step tighter from green: brown..... black.... will not make a huge difference?

I have an APE crank in and I have no intentions to drive within the speed limits nor rev limits either. Too tight is not good either. I have to find out if Brown or Black is the way.
No problem to buy new, the not old good greens will fill my old empty K2 case.

Edit:
I have vague memories of my old shells my tuner installed 1983 and I removed 2012. They had brownish markings I thought was burned residues of old green. It might been brown shells in due to measurements, not crank and case markings.

[PeWe]

I should have checked the old shells better when replacing them 2012/13.
The markings were gone on most of them, but 2, 3 have clear brown markings. I was too sure about green.

I measured the old brown (~40.000kms) and newer green (~5000kms).
The brown is thicker. I measured with a micrometer, not good for absolute thickness. The relative numbers are interesting to very how much thicker the brown is.

- The question now is how much the difference is between existing green with 0.0020" clearance and brown then black. One step like Hondaman wrote in a thread when reaching 0.0022 might be the correct move.

[iron_worker]

I thought the .0018" limit was for new spec bikes. IIRC the serviceable limit is .0028". Hopefully someone can confirm that.

I know that engines that are planned to spend a lot of their time at high RPM tend to shoot for a slightly looser clearance.

IW

[mystic_1]

Clymer says:

[PeWe]

I have to check with brown shells and verify the clearances before deciding which to use.
My last shells were green. They look very good, no scuff marks at all after 5000kms.

My older browns that have almost 10 times more use have scuff marks.
Used oil back in the 80's was car oils, mostly Castrol GTX2 and Mobil 1.

Last shells got Castrol Actevo (mineral) 10-40 (1000kms), 20-50 (1000kms). The latter got additional zinc (500kms). Then changed to Red Line motorcycle oil (synth) 20w-50 (2500kms) that feels very oily and must be very good for the crank and cam bearings.

I have read threads about crank shells and several guys wrote that 0.0020 clearance is good. More clearance, more oil flow cooling the bearings.
My thoughts about correct clearance is to have a good start when finally asssemble the cases. Start with max clearance feels not good.
But Honda might been wrong when specify the clerarances...? There is a huge diff between max clearance and when to replace bearings. 0.0018 vs 0.0032

[PeWe]

Now with new brown shells. Not that much tighter than with my almost new green shells with around 5000kms.
Just under 0.0020" / 0.050mm, before the other side of 0.0020" / 0.050mm