Topic: IDK Numero Dos - 1975 Honda CB400F

[minimo]

Eliminate doubt.

That’s what this is gonna be about. Like probably most of you who’ve followed this so far (thanks for that) I have a strong feeling the knocking issue has been more cam chain related. But I also fear that if it’s not gonna be that and it’s probably some other issue, like the crankshaft/rods or that needle bearing that gave me the squirts when one of the needles popped off. So I figured while I was in the neighborhood...

And maybe like some of you I especially  loathe dealing with OIL. I hate filling oil. I hate draining oil. I hate when it’s on my hands; even when I wear gloves. Worse is repeating the process more than necessary so that in large part is the reason for me opening the case - hopefully for the last time.

I have some experience with Plastigauge on a previous rebuild of a 1977 CB550F so I’m already familiar with the process. At first glance I’m going to say that the connecting rod and crankshaft bearings are all probably gonna be fine but just to say that I’ve checked and so I don’t go crazy having to check this again...


Sent from my iPhone using Tapatalk

[minimo]

The needle bearing was intact.

The cam chain push rod was binding so I reamed out the hole a little bit to allow for free movement - though it was binding outside of its intended travel so probably a non-issue. Everything else so far on visual inspection looked ok. No visible or outlandish wear anywhere.

So, onto the measurements.

Plastigauge the mains at crankshaft, 7.5 ft-lbs torque: left to right (in inches: 0.002” = 0.051mm)

1 - 0.002”
2 - 0.002”
3 - 0.002”
4 - 0.001”
5 - 0.002”


Next, Connecting Rods:

OD of crankshaft pins
1 - 32mm,
2 - 32mm
3 - 32mm
4 - 32mm

I measured these in metric with my calipers.
When measuring #4, there was a difference of 0.95mm and from appearances looked worn compared to the rest...

The space in the rods was measured vertically and in metric.

Still, I doubt that even 1mm slop would make the kind of knocking sound that I’ve been getting. I’m tempted to button this all back up




Sent from my iPhone using Tapatalk

[strynboen]

its 10 times the normal tolerence...så yes..the problem is there..

0,02 inch ? in metric..

[Little_Phil]

The connecting rod to crank gaps should also be measured with plastigauge. My guess, maybe more than one will fail.
And replace your primary chain if you have not done so.

[minimo]

Here’s the Plastigauge I’m using - METRIC on left; INCH on right.


I used inch because I’m a dumb American, strynboen. Here, we only use metric to measure the size of our dumb plastic soda bottles; in liters




Sent from my iPhone using Tapatalk

[strynboen]

yes but the bike is metric..just the tires is fzuk..strange messurings..most of the vorld..russia germany greenland Japan italy..use metric even sveden have thanged to metric..so your inch days are getting fewer..tires and vater tubes is also goin ;Dg metric..

[minimo]

The connecting rod to crank gaps should also be measured with plastigauge. My guess, maybe more than one will fail.
And replace your primary chain if you have not done so.

How do you do this without moving the connecting rods; effectively smearing the Plastigauge?
Also, torque to yield bolts should not be reused, correct? Is there a viable alternative as it appears that Honda part # 13213-333-003. David Silver the the best option? Quite pricey https://www.davidsilverspares.com/CB400F0-SUPER-SPORT-1975-USA/part_162413/


Sent from my iPhone using Tapatalk

[minimo]

yes but the bike is metric..just the tires is fzuk..strange messurings..most of the vorld..russia germany greenland Japan italy..use metric even sveden have thanged to metric..so your inch days are getting fewer..tires and vater tubes is also goin ;Dg metric..

While all this is true, the manual has the clearance specs in inches, I think

And while I have your attention to these charts, anyone have a brilliant translation or link on how to read these?


Sent from my iPhone using Tapatalk

[minimo]

I was able to Plastiguage the connecting rods tonight, with some difficulty keeping the rods steady... Here are the clearances, eh hem, in inches:

1) 0.0015”
2) 0.0015”
3) 0.0015”
4) 0.003”

There’s considerable slop on the #4 con rod. I can even move the rod up and down and it jiggles. No bueno. It’s maybe no coincidence too that was the same plug hole #4 with the blown out threads. So looks like I’ll be replacing some bearings, at least on the con rods and the crankshaft mains on #4. Any reason I should replace the others if they’re within spec? They all have a fair amount of scoring; no pitting. Change them out anyway?


Sent from my iPhone using Tapatalk

[Little_Phil]

Full set of shells is a lot of $$$. Hopefully #4 is the source of your noise. If you want opinions on bearing surfaces, post pics on the SOHC/4 Bikes section. The others do look within dimensional tolerance though.

[minimo]

Thanks, Lil’Phil. I may venture out of my own project shell to hone in on some of these details.

The kind of slop I’m experiencing on the #4 con rod I imagine would be enough to notice something off; a knocking, perhaps? We shall see. I’m also addressing a dumb lock down issue on the cam chain adjuster push rod (or lackthereof) so it could be one or the other. I actually would like to know. Sometimes I wish I had x-ray and slo-Mo visión to easily detect this sorta thing


Sent from my iPhone using Tapatalk

[minimo]

I mean, #4 con rod bearings were so bad that even the backsides were rubbed out - I couldn’t even read the stamped markings. The shells even spin around loosely when the con rod is torqued down.

Luckily, the mains look ok clearance-wise. I’m replacing the last set on the end closest to #4 con rod as it was measuring slightly off compared to the rest.

Now it’s a waiting game with David Silver Spares. Hopefully he’s not on holiday. Last time it felt like it took a couple of weeks to get parts. I’m waiting as fast as I can.

The ride weather as of late has been ideal and optimal here in LA. I hope to catch some of that soon.


Sent from my iPhone using Tapatalk

[ttr400]

I will try to help you out with some explanations of the Honda bearing charts.

First off, you should only work in metric...why? well we have moved on its not the 60's anymore. get your mind around it and you will find it is much easier to work in multiples of 10.

The Honda bearing charts, that you have shown. these are in Metric, not imperial.

The clearances specified are in Microns. 1.0mm = 1000 microns (the little symbol that looks like a U with a tail to it).

The Honda std measurements:
Main bearing Journal: (same for big end journal) Dia 32.0 + 0.0, - 0.010-0.030 (-10-30 microns) this is 31.99-31.97
Big end rod dia: 35.0 -0.0, + 0.008-0.024 (8-24 microns) depending on rod size 1,2 or 3
Main case inside dia: same as rod dia. case marked  A B or C

So Crank mains and big ends should not be more than 32.0mm can go down to 31.97mm.
Rod ID should not be less than 35.0mm can go up to 35.024.
Main case ID, same as for Rod ID.

Std clearance: Mains = 20-50 microns.
Std clearance: big ends = 18-48 microns

So looking at your clearances:
Main journals: 0.002" = 51 microns......measure again with a micrometer.
Main journal #4 : 0.001" = 25 microns
Big end journals: 0.0015" = 38 microns
Big end journal #4: 0.003" = 76 microns...........measure again with a micrometer. may need a new rod and or crankshaft.

Your measurement of the crank journals of 32.0mm.......measure again with a micrometer, if you are under 31.97 crank will need to be replaced.

Phew. hope i have not made it sound too complicated. if i have made any mistakes or missed out something, let me know.

Kevin

[minimo]

Thanks for the explanation, Kevin. I was wondering what that “mu” symbol was. Ok, so I’m definitely within bearing clearance spec across all rods except for #4, as totally expected. But, that you’re suggesting a possible replacement of a complete rod or crankshaft... I would beg to differ.
I remeasured the journals, this time in millimeters and here’s what I’m getting with my trusty pair of Mitutoyo digital calipers:

Crankshaft journals, O.D. (mm):
1 - 31.99
2 - 31.99
3 - 32.00
4 - 32.00

Connecting rods, I.D. (mm):
1 - 31.99
2 - 31.99
3 - 31.99
4 - 31.99

Pretty darn immaculate, no? Seriously, I’ve gone over now a few times and none of my journals read below 31.99

My case is marked BBBAA

Shouldn’t a bearing replacement on #4 for both rod and crankshaft/case be sufficient? Which bearing color, respectively should I choose (though I already have Browns on order)?



Sent from my iPhone using Tapatalk

[ttr400]

If these are accurate measurements then yes you are within spec.

I assume you are taking these measurements with a Vernier caliper? if so not really that accurate.

For the big end ID on the rods i use a 3 point bore gauge. I also see you are measuring with the bearings installed.

To determine what rods you have 1.2 or 3 (are the markings visible) measure without the bearings.

In my experience when a bearing spins it often enlarges the big end ID or makes it oval. sometimes makes the OD on the crank smaller.

Kevin

[minimo]

Yes, vernier calipers are the best I got at the moment. As for the rod markings, there appears to be both letter and numbers that all read “2” and “B” across 1-4.

And on my last batch of measurements, I measured strictly the journals; lifted the crankshaft out of the case. No bearings.

[minimo]

A peek at #4 connecting rod bearings



Sent from my iPhone using Tapatalk

[Little_Phil]

Again only familiar with 500. Honda used colours as names for different bearing sizes. And when new a colour was dabbed on the bearing, but that usually disappears with age. Batch nos on the back of bearings may or may not mean the size, but the same nos probably indicates that they are at least all the same size.
The rod (with bolts but no bearing) was graded by weight and marked with a letter.
Before putting everything back together investigate the oil channels in the crank that feed the bearings.

[calj737]

Minimo - Since Kevin has come along, I'll only reinforce his point: use micrometers for these measurements. If you don't have any, buy some. If you don't want to buy them, take the parts to a machine shop and have them measure these parts.

Verniers are not nearly accurate enough for round interior/exterior measurements. You could easily be off many hundredths in your readings without the ability to discern it. A decent set of micrometers for 1" & 2" outside, and 1" and 2" inside is well worth the money. You will need them countless times if you plan to build/restore these bikes.

[strynboen]

you can bay some akurate china mikrometers..they are fine for the Money.
.baying them on e bay is the lovest cost..but give a month vating..for the dubbel preis you can get the same instrument in the local shop..

[calj737]

1-day delivery
https://www.amazon.com/Anytime-Tools-Micrometer-Precision-Machinist/dp/B0045UZGSC/ref=sr_1_6?ie=UTF8&qid=1539084542&sr=8-6&keywords=micrometers

[minimo]

Micrometer. Copy that. I will look into measuring these journals with a proper set and report back. Thank yous!


Sent from my iPhone using Tapatalk

[minimo]

Borrowed a friend’s Mitutoyo micrometer (it’s in inches so I’ll note the mm conversion) and got the following readings:

Main Bearing Journals
1 - 31.9777mm
2 - 31.9862mm
3 - 31.9862mm
4 - 31.9862mm
5 - 31.9887mm

Big End Rod Journals
1 - 31.9887mm
2 - 31.9887mm
3 - 31.9887mm
4 - 31.7830mm (up/down), 31.9887mm (sides)

Already with the micrometer I can feel the score marks that I couldn’t notice at a glance. I would take the larger side to side measurement of that journal and spin the micrometer over to the up/down axis and there’s significant slop, well, 0.2057mm worth.



Crankshaft replacement in order?

It’s late now and I’ll get around to measuring the rods maybe tomorrow. May end up getting a whole assembly of crankshaft and rods that are in better condition via eBay. What do ya say?


Sent from my iPhone using Tapatalk

[calj737]

I say nicely done snatching the micrometers  See the difference in accuracy? With those, you know exactly how badly worn the parts are. Now, if only those went missing in your garage....

I’ll let Kevin advise you on a get-well plan given his extraordinary expertise with the 400.

[ttr400]

Hi,

Much better as cal has pointed out.

As expected the #4 rod journal is way out, Oval i suspect. i can also see from the bearing photo that it has spun around. yes another crank is in order.

You might be OK with the rod but i would suggest taking a measurement without the bearing shells fitted, torque the cap first.

I have 2 cranks lying in my workshop, one for a 550 and a 400F both with the same as what you have. on both cranks i also had to replace the rods.

Years ago i had a under size journal on a crank, i had it hard welded/ground and nitrided.............did not last very long. but was worth a try. as it was a nice knife edged lightened and polished etc etc.

Kevin