Topic: 1975 CB400F Crankshaft/Case Questions

[CB400JAY]

I just split the cases of my early matching numbers(exact match) 1975 CB400F to change the cam chain and tensioner.  I believe that the bottom case was changed at some point in the past. I didn't think that you should change only one half.   First the top case has discoloration in the clutch area while the lower case does not.  Second the dowel pins to align the two halves are missing.  Is it OK to change just the lower case?  I checked the side clearance on the connecting rods and it measured .008in.  All four rods were very close. This is within specs for most Honda fours but for some reason the factory shop manual for the CB350F-CB400F shows it to be .0008-.0028in with a service limit of .0059in. This just does not to seem right to me. Anybody have any thoughts on this?  Is the factory manual wrong?

   

[bryanj]

No its not ok to change one half of crankcase

[CB400JAY]

No its not ok to change one half of crankcase

What is the reason?

[jakec]

They get machined together so the crankshaft bore is only matched exactly to two halves machined together.  It could be possible the pins are missing because the crank didn't fit with the pins in place, maybe.

[CB400JAY]

They get machined together so the crankshaft bore is only matched exactly to two halves machined together.  It could be possible the pins are missing because the crank didn't fit with the pins in place, maybe.

That is a VERY interesting theory.

[754]

Yes they are matched.never meant to be swapped.
 I may have cases, where are you located ?

[CB400JAY]

Yes they are matched.never meant to be swapped.
 I may have cases, where are you located ?

Thanks so much for the offer.  Going to check things out to see if I can safely use the current cases.  Don't want to loose the matching numbers. As far as I can tell this change was done very early in the bikes life and it lived on for a very long time. I am in LI, NY.  Pretty far away from you. I remain concerned about the big end side clearance as stated in the factory shop manual.  It just can't be right.

[754]

What I'd your issue with side clearance, ? the oil and bearing fit has done its job by the time it gets to the sides. .
Too much drag  robs horsepower.l

[bryanj]

Any Honda with same frame and engine number is suspicious as it just never happened out of the crate,

Any chance of pictures of the number stampings to see if they look original?

[CB400JAY]

Any Honda with same frame and engine number is suspicious as it just never happened out of the crate,

Any chance of pictures of the number stampings to see if they look original?

That is just wrong.  I worked for several Honda dealerships when these bikes were new and even removed some from the crate.  For some reason the numbers were always very close.  I saw several within 10 and a few within 1 or 2 so it is very possible that a few matching numbered examples do exist.  This is a very early example built in 9/74 when the numbers were often very close, some even matching. I've seen enough Honda engine numbers to know when they are original and these definitely are.

Here is an example of a later one that is 1 number off.

https://www.bonhams.com/auctions/24877/lot/405/

[CB400JAY]

What I'd your is due with side clearance, ? the oil and bearing fit has done its job by the time it gets to the sides. .
Too much drag  robs horsepower.l

Not exactly sure what you mean in your first sentence before the ?. I agree completely with the rest of what you said.  I just cannot understand the clearance spec stated in the factory shop manual as it makes no sense.  It is way too small and not in line with any other Honda Four of the same era that I could find.

[Nurse Julie]

Any Honda with same frame and engine number is suspicious as it just never happened out of the crate,

Any chance of pictures of the number stampings to see if they look original?

That is just wrong.  I worked for several Honda dealerships when these bikes were new and even removed some from the crate.  For some reason the numbers were always very close.  I saw several within 10 and a few within 1 or 2 so it is very possible that a few matching numbered examples do exist.  This is a very early example built in 9/74 when the numbers were often very close, some even matching. I've seen enough Honda engine numbers to know when they are original and these definitely are.

Here is an example of a later one that is 1 number off.

https://www.bonhams.com/auctions/24877/lot/405/

Those numbers are not correct, if you read down to the bottom of the listing, it tells you the correct VIN/ engine number. This is what the listing says
' The frame number is CB400F-1077397. The engine number is CB400FE-1073196' .
That being a UK bike, a difference of about 4000 in the numbers is about the norm. Mine is about 4200 numbers apart and was built at a similar time to that yellow one.

[bryanj]

I uncrated, built, pdi'd, 1st serviced ans looked after several hundred Hondas when working at Honda and non franchised dealers in the 70's in UK and never came accross anything closer than 20 on numbers

[Nurse Julie]

Going back to the original question, if you look in the Service book but look at the specs in mm's, it does make sense. Assembly standard 0.02-0.07mm with a service limit of 0.15mm. So yours measure 0.008 Inches =
0.2032 Millimeters, so they are beyond spec in your case.

[CB400JAY]

Any Honda with same frame and engine number is suspicious as it just never happened out of the crate,

Any chance of pictures of the number stampings to see if they look original?

That is just wrong.  I worked for several Honda dealerships when these bikes were new and even removed some from the crate.  For some reason the numbers were always very close.  I saw several within 10 and a few within 1 or 2 so it is very possible that a few matching numbered examples do exist.  This is a very early example built in 9/74 when the numbers were often very close, some even matching. I've seen enough Honda engine numbers to know when they are original and these definitely are.

Here is an example of a later one that is 1 number off.

https://www.bonhams.com/auctions/24877/lot/405/

Those numbers are not correct, if you read down to the bottom of the listing, it tells you the correct VIN/ engine number. This is what the listing says
' The frame number is CB400F-1077397. The engine number is CB400FE-1073196' .
That being a UK bike, a difference of about 4000 in the numbers is about the norm. Mine is about 4200 numbers apart and was built at a similar time to that yellow one.

You are correct, I didn't see the 3rd set of numbers in the ad.  The first 2 were 1 number apart as was the description of the bike.  That being said the ad proves nothing. 

[754]

I think number  match does exist, but is very very seldom seen.
And I am pretty sure more bogus number match are out there than legit.
 
 As far as mis matching cases go , here are some of the problems . Side stagger  if mismatched don't line up perfectly on the seam , then your rod side clearance can be two sizes .
 If the half circle of one case is a thousandth  of an inch off to the other case, your bearings are not forming  a circle..not to mention that you may need 2 different number bearings.. but unless you know what the unmarked case came with, you will never know.
 That said , it can and has worked in a few cases, but it may or may not.... introducing  unknowns  in a engine build never helps or adds any value.

[CB400JAY]

Going back to the original question, if you look in the Service book but look at the specs in mm's, it does make sense. Assembly standard 0.02-0.07mm with a service limit of 0.15mm. So yours measure 0.008 Inches =
0.2032 Millimeters, so they are beyond spec in your case.

Yes, but the spec in the FSM is very tight compared to all the other Honda Fours I've researched.  Has anyone else checked their CB400F crankshaft and found the clearance to be within the FSM specs?

 BTW... I just checked a second one and it was almost the same as mine. 

[CB400JAY]

I uncrated, built, pdi'd, 1st serviced ans looked after several hundred Hondas when working at Honda and non franchised dealers in the 70's in UK and never came accross anything closer than 20 on numbers

I also own a CL77 that is 10 numbers off.  Maybe just the luck of the draw. 

[bryanj]

The numbers seem to get farther apart the longer into a production run the bike goes.
I believe engines were built in a different plant, numbered sequentialy in production and delivered to the production line in number order but engines that did not pass QC were pulled and either scrapped or reworked and returned to line. I have no concrete proof of this but have read it elswhere, it would also be reasonable engineering practice

[CB400JAY]

The numbers seem to get farther apart the longer into a production run the bike goes.
I believe engines were built in a different plant, numbered sequentialy in production and delivered to the production line in number order but engines that did not pass QC were pulled and either scrapped or reworked and returned to line. I have no concrete proof of this but have read it elswhere, it would also be reasonable engineering practice

I agree with everything you said.  That's always been my impression as well. 

There was a 1975 CB400f sold on Ebay recently that was 1 number apart.  Very early example built the same month as mine but a few hundred numbers earlier.


 

[bryanj]

If we assume that Honda got better at machining sohc fours as the years went on failures in the 400 should have been less as it was almost the last one. Just hypothesizing

[CB400JAY]

Just found this post on the forum from a few months back.  He had the same issue with side clearance that I have.  Just didn't question the FSM specs or do any additional research. Here is a quote:

"What concerns me is the con rod big end side clearance should be between 0.02 - 0.07mm with service limit of 0.15mm. I unfortunaly don't have a photo but a 0.15mm feeler gauge fit no problem. Has anyone check this tolerance before? Should I be concerned about this? Fixing this seems....impossible... without replacing the whole assembly"

 
http://forums.sohc4.net/index.php/topic,182495.msg2112687.html#msg2112687


It is my position that the original Honda shop manual is wrong.  The correct number should be more along the lines of what the CB500 Four manual says which is 0.0047in to 0.0106in with a service limit of 0.0138in.

[CB400JAY]

I just pulled this photo off of an Ebay auction.  Shows another set of CB400F cases with the exact same discoloration mismatch as mine.  I now believe that my cases are NOT mismatched and some came from the factory like this. 

[jakec]

The top was painted and bottom not, from factory. Since the discoloration is only on the inside maybe it has to do with how the paint cured. Assuming they painted overspray on the insides.

[754]

I think oil stain.. I see it in most 750,s different shades  from different oils.
 I was thinking, if someone was into the transmission,  and top end was still on , the bottom case may have got thoroughly cleaned, and top stayed the way it was ..

[ttr400]

This is common on the 400's that i have done over the years.
The gold colour is i think Aludine coating. not sure why Honda did this, Aludine coatings can be done on aluminium surfaces to give extra protection or as a base/primer prior to painting.

I doubt you have mismatched cases, but easy to check if the engine is apart. bolt the cases together and mic the bores. but if it's been running for years then i don't think you have anything to worry about.

Kevin

[CB400JAY]

This is common on the 400's that i have done over the years.
The gold colour is i think Aludine coating. not sure why Honda did this, Aludine coatings can be done on aluminium surfaces to give extra protection or as a base/primer prior to painting.

I doubt you have mismatched cases, but easy to check if the engine is apart. bolt the cases together and mic the bores. but if it's been running for years then i don't think you have anything to worry about.

Kevin

Thanks so much for the explanation.  Makes a lot of sense.  I didn't know that only the top case was painted at the factory. What made me think the cases were mismatched was the color and the lack of dowel pins.  Everything looks good and I am sure that all is OK and the cases were in fact matched. As this is a very early example maybe that explains the lack of dowel pins?  I will be a installing one of your cam chain tensioner horseshoes.  Nice work!!

[bryanj]

Should all have dowel pins to locate for machining, fit pins and mate casings the see if one half is offset to the other at the bearing locations, if there is a feelable step with your fingernail they are mismatched cases

[754]

 If they  are mismatched,  and the case is not closing at the join line, next step would be ...remove dowels to allow it to line up..

[CB400JAY]

I installed a new set of dowel pins and plastiguaged the crank.  Everything is fine, no issues.

[754]

And transmission bearings fit bad cases squeeze together by hand, correct ?