Topic: A 1975 CB400F 102.000 km (65000 mi) complete engine rebuild

[supersports400]

I finished my cylinder head, so I brought it away for the valve cutting job, I'll have it back somewhere next week.
Meanwhile I decided to work on the oil pump, kind off a rebuild I guess.

When doing a full  engine rebuild, it’s necessary to take a good look at the oil pump. Since NOS oil umps are rarely seen on eBay and other market places, it’s worth doing the best you can, and find some good used pumps to make  good one from the best parts.

When I dismantled the rockers and saw the damage on the cam, I knew I should have a look in the oil pump for any damage. The chrome of the rocker surface was mostly gone. These chrome particles are very hard, and sometimes brake out of the surface in pieces. On at least two rockers this was the case. These pieces are not filtered out before they can reach the oil pump, so these particles will ground the pump lobs. Small damages or not so bad, but bigger damages or a lot of small damages can lead to the fact that the oil pump doesn’t pressurize the oil enough for the main bearings especially when the oil is hot (low viscosity).

Over the years I bought two other second hand pumps from low mile engines. I want to build one good pump out of three pumps.

First of all I dismantled all pumps carefully, and cleaned the parts thoroughly with petrol (see picture)

My own (original mounted on my CB400) pump (pump 1) :

I found that my pump was indeed damaged (inner / outer rotor), and since it’s from a high mileage machine, it also showed (normal) wear between the outer rotor and pump housing (see picture 2 and 3).

Pump 2 (according to the previous owner the engine did only 10.000 miles and the price 20 USD) :

I found that this pump also had damaged rotor lobes, less that mine, but nevertheless, damaged. I also found that the pump gear was damaged (see picture 2). Overall the parts showed less wear then pump nr. 1 I would say that indeed the pump did less then 65.000 mile, but 10.000 miles is a little too positive, or the PO never changed oil during the 10.000 miles.

Pump 3 (I bought this pump on  a local swap meet, the seller said something like low mileage, but didn’t know how much it actually did, but the price was 1 euro, so I bought it).

I found an almost perfect rotor set in this pump, no damaged rotor lobes, nothing at all. The pump did however turn a little heavy, but smooth. I also saw that the gear on the pump was different then the other ones, I checked with my parts manuals, but there’s no info about parts in the pump, and there’s only one part number for a complete pump, strange, but after working on older Honda’s you get used to these things. The dimensions of the important area’s where exactly the same as the other ones.

After the first impressions I started measuring. The most important dimensions of an oil pump are the size of the lobes, the amount of play between both rotors and the play between the rotor and the pump housing.

Play between the inner and outer rotor (measured as in picture 4) :

Pump 1 : 0.15 mm
Pump 2 : 0.10 mm
Pump 3 : 0.05 mm

I choose to go further with rotor set of pump 3, and measured the play between outer rotor and the pump housings :

Outer rotor 3 - rotor housing 1 : 0.05 mm
Outer rotor 3 - rotor housing 2 : 0.10 mm
Outer rotor 3 – rotor housing 3 : 0.10 mm

I decided to use the rotor set from pump 3 in the main rotor housing of pump 1, and measured it again, resulting in the same numbers.

The gear and shaft from pump 1 was the best, and also a had the tightest fit in rotor housing 1, so another part selected.

Now, I only have to choose between 3 oil pump main body's, and the best secondary pump rotor set (the pump of the CB400F consists of two pumps, one (big) for the crank and head, the other one (small) for the transmission (see picture 5 to see the pump main body rotor surface)

[supersports400]

I measured the small rotor sets in the same way and found out  that rotor set of pump 3 was the best (0.05 mm), and the play between the outer rotor and oil pump main body number 2 was the best fit (0.05 mm). Non of the rotors where damaged in any way (see pictures 1 and 2)

The secondary oil pump cover of oil pump number 2 was really smooth,, so I use that one too (see picture 3).

So, the complete assembly is consisting of the main rotor set of pump 3, main rotor housing of  pump 1, gear / shaft from pump 1, secondary rotor set from pump 3, the main pump housing of pump 2 and cover (and bolts) from pump 2. I also used the pressure relief valve from pump 2, but the spring from pump 1 (stiffer).

The next step is to measure the space between the main rotors side ends and the housing. This space is regulated by the height of the main rotor housing. I used plastigage. to measure it, and found out that the play was more than 0.2 mm  The rotor is made of steel and the housing is made of aluminium, and thus the expansion coefficients differ a lot (steel has a much bigger expansion coefficient then aluminum. From that point the play between rotors and housing can be 0 / +.  For safety I choose for 0.02 mm play between the surfaces (20 micrometer). I  grinded off by hand (with sand paper 800 on a very flat table) the main rotor housing 0.18 mm (I did this in 3 steps) to make sure not going too far. This resulting in 0.02 mm play between rotor and main rotor housing.

After assembling it turned very smooth and so I now I only had to figure out what size of O-ring to use between the main rotor housing and the main pump housing.

As this O-ring is not mentioned in the parts manual, I did measure depth and diameters (I.D. and O.D.) of the O-ring grove itself. I chose a viton O-ring that is 25 % bigger in diameter (thickness) then the groove.

Now I only have to assemble the O-ring in the oil pump, and store it for later use when building everything together. From all other parts I made another pump (reserve), in the same way.

The play between the rotors is 0.1 mm, the play between rotor and housing is 0.1 mm, and I refurbished the lobs of the inner rotor a bit with very fine sanding paper. The rest of the parts are for spare (or when I find another good pump or two to go through the same process)

What Honda says about the specs of the oil pump :

Maximum play between the rotors :          0.30 mm
Maximum play between rotor and housing :   0.35 mm

There are no further specifications of play between parts, so you also can conclude that all the oil pumps I started with where in fact within specifications, so, why all the hassle ?

My impression on these specifications are different then Honda had in the 70’s. it’s also known from the 70’s that these sohc4 engines where prone to early cam and rocker wear. One reason was the use of low quality mineral oils (there are also good quality mineral oils), and the other reason where the tolerances of parts in an given engine.

I always use full synthetic oil in rebuild engines. I have very good experiences with Castrol ( power 1 GPS 4T 10W-30 or 10W-40). I don’t want to start an oil debate, this is what I use.

When the engine is real hot, on a hot day, the pump should be capable of building up pressure. The smaller he play between the important parts, the less leak between the parts and rotors self . So the better the specifications are, the more guaranteed this will be. I’m investing a lot of money in this rebuild, and therefore I don’t want to ruin a my engine with a bad oil pump. I like to ride it fast and reliable, for a long time.

Jensen

[fasturd]

Have you thoght about doing the modified pump using cb750 bits? I have seen the yoshima mods on another web site he used these mods on his high hp 400 race motors. It builds much more pressure than stock pump.

[supersports400]

Hi fasturd,

Yes thought about it, studied the case and decided to stick to the CB400F oil pump, but with trying to get this as good as possible.
A lot of machining is necessary to fit those parts in, and at the moment I have enough machining under my hands. And there's another reason not to o that, and that reason is power loss over a very big oil pump for this little machine. As I did a mild flow job on the head, keep the stock carbs and exhaust, I will stick to the specification red line of around 10.000 rpm. However thanks for the thought,

Jensen

[flatcat]

 Hey word of note. Be careful of synthetic oils in your wet clutch engines. I worked as a engine machinist for yikes 21 years and Ive done a lot of Jap. engines and the older cb's hate oil that is too slick. Usually it only causes clutch slippage,but other cavitation issues have been spotted. The cavitation at worst will cause oil starvation and low oil psi,and will cause power loss at different rpm levels.
 The rebuild is looking nice. Keep the dinosaurs alive! 

[strynboen]

hey ve have lot of trobbels vith clutch in aur yamaha fs1 club..it endet vit juse of single grade sae 30 oil..vith aut any additives. drive alså vith it on my cd-50.bur it is not yousble on our hondaes,,and please no new oil tread/var..think you are right
syntetic are overkill..on this old dinusar bikes

[supersports400]

Hi,

For years I have very good results with full synthetics oils in classic Honda's, but before switching to these kind of oils it's wise to prepare the engine for it.

Before I switched over to synthetic oil (at 75.000 km) I cleaned the oil pan, changed clutch plates and replaced the clutch springs for heavier ones. Never had problems other then mentioned above, but like I said you should prepare for the changeover.

Jensen

[strynboen]

think the trobbel must be ,,vhen the syntetic not are for mc use..i have thosen theper oil,,in spefikation..and thance it 2 times year...there is 1000 vays to do this..importen is to take bottom of engine and klean sump,,and filter house,,,and use orginal honda filters..
lets go back to yours fantastic history..

[supersports400]

Hi fasturd,

Thought about it again, and decided to build one oil pump with a CB750K rotor set. I have three oil pump housings, and I'll use one housing to make this modification.

The original rotor has a height of 12.00 mm, the CB750K rotor has a height of (modified) 15.5 mm.
If the flow would be linear to the height of the rotor (that's not the case, but a good approach), the flow of the modified pump would increase by 30%.

Since the engine drives the oil pump, the oil pump will reduce the output power of the engine, at least by 30% of it's initial power consumption. I spoke to a few specialists and they say that an oil pump of these engines will consume at least 3 to 4 HP or even more at 10.000 rpm, depending on the heat of the engine and the viscosity of the oil, so it will use at least an extra HP, thus resulting of using 5 HP. This is one of the reason why I still feel some doubt to walk this way, but since I have a choice between oil pumps, I'll go down this road.

Since the flow resistance of the system stays the same, the pressure will increase (dictated by physics). I rather invest power in flow than in a higher pressure. The most important part of the engine (lubrication / cooling) is the cylinder head. I want that 30% of capacity of the pump working for the cylinder head. If I don't change anything this extra 30 % capacity will affect all lubrication points of the system, and I don't want that.

To change this I have to decrease the flow through the oil orifice's between cylinder and head. To stay on the save side I will increase the flow by 15 % by increasing the surface area of the throughput by 15 %.

Another approach (instead of chancing the oil orifice) would be using oil with a lower viscosity like 5W20 or something like that.
I've not decided it yet, first I have to locate a nice rotor set of a CB750K oil pump, before even start machining the oil lump housing.

Jensen

[fasturd]

I assume you watch Ebay USA for parts? I also have a local provate supplier of NOS items I can check with him regarding oil pump parts. I am still searching for the article on the mods. It was from the day and it was a mod either Kaz or Pops was doing on his high performance street and race bikes. I will let you know.
Good luck,
Bill

[supersports400]

Hi fasturd,

I have the article (both), but I don't have the parts. I watch Ebay worldwide, I don't care where it comes from.
It seems that the CB400F rotors don't have part numbers, so I expect that Honda doesn't sell them without a complete pump.
Maybe this is the same for the CB750 rotors ?

Jensen

[SohRon]

Thank you for such an informative thread. Really learning a lot here. Makes me want to go out and tear into my spare engine...

[supersports400]

Update 10-03 2010

After splitting the cases a few weeks ago, I checked every part carefully and measured if necessary. After that I made a list of parts witch should be replaced,  and a list of parts  I like to have replaced (but not really necessary). Locating and buying these parts was what I did the last few weeks.

Parts that should be replaced are :

all bearings including crank bearings
all seals, o-rings, packing’s etc.
one shift fork shaft (bent a little bit, but never noticed while shifting)
kick starter shaft and kick starter (worn splines, not to bad, but loose enough)
clutch plates and clutch springs
primary chain, cam chain
primary chain guides
primary damper rubbers
and a lot of small parts

Parts I like to have replaced :

Counter shaft (where the sprocket is mounted on)
Advance unit, points, condensers
fifth gear (counter shaft)
sixth gear, both

Earlier I bought a set of conrods (couldn’t  resisting because of it’s price), so these will be part of the refurbished engine too.

I bought all parts already, now waiting for delivery.

My top crankcase is at the painter, for a paint job, together with the clutch cover, dynamo cover and the sprocket cover.

Just letting you all now that the project didn’t ended.

Jensen

[fastbroshi]

Man I like your style.  Super detailed.  The mostly stock resto isn't my style but I can appreciate your effort and thoroughness.  I'd love to hear this run when it's done.

[fasturd]

The parts collecting before the build is one of my favorite parts. The challenge is being able to get the items you really need when it come to the final moment of assembly... Then I usually change my mind and I still end up waiting for a much needed "new/different" part.

Great bunch of info it should be a great little motor when it is done.

My bike needs to get finished in the next 5-7 days as there is a big local show it was accepted into. Should be fun to represent the SOHCs at a CHOPPER show! lol.

[supersports400]

Hi fastbroshi and fasturd,

Promised, I will drop a video at youtube when ready with rebuilding (probably a dynoyet session) after the breaking-in period.
I collected parts years before the actual rebuild, just in case if I needed them. Now, after opening the cases it's clear that I didn't have all the parts needed, like a camshaft for example. Some parts I have lying around are probably not needed, like a new (complete) dynamo, primary shaft etc. Some parts where unobtainable for the price I had in mind, but now I had to buy them.

I'm also in doubt painting the frame or not. Now the engine is removed and my front fork is removed, it's just a small step to remove the rear fork and rear wheel. A lot of small sctratches and chips broken of in all those years.

It's also time to start my next project, a Honda dream (C77) from 1964, but won't take as much time as this CB400F because I know my way around these engines, I guess another two months before completion, just before the summer ends, and a breaking in period in September.

Jensen

[fasturd]

Our snow is melting here so I should be riding something modern in the next week or so... I hate taking old bikes out until all the slop is gone, they are just too hard to clean and get all of the salt off of them!

The dyno info will be interesting.

Good luck,
Bill

[supersports400]

Yes,

especially compared with the dyno runs in the beginning of this thread.

Jensen

[supersports400]

update 29-03-2010

examination of parts part I :

After opening the crankcase everything seemed nice and shiny, but as usual, the devil is in the detail, and the devil was in my transmission. The first impression was good, but I knew something should be wrong, because my oil pump just was too much damaged. After disassembling the gears from the shaft and cleaning the gears thoroughly, I found heavy pitting on the the top gear combination.

I tried to make a good pictures of it, and it clearly shows that this gear has severe damage. These images show exactly what pitting looks like, the top layer of hardened steel is completely disintegrated. Both top gears where damaged, but not in the same way. The counter shaft top gear is damaged the most.

I expected a lot, but not this amount of severe pitting in gears from an engine always maintained good with good (mineral) oil. I saw a lot of this pitting on my early Honda's, but these are known for the hardening errors, and thus pitting.

Jensen

[fasturd]

This is great info. Will be helpful to know what I am really looking at when I get into my other 400 motor.

[supersports400]

Hi Fasturd,

Well, I hope that it is not as bad as mine, and it probably won't be either.
Like I wrote earlier, the PO rode this bike as if it was a BMW, and probably used the top gear as a overdrive while doing 2000 or 3000 rpm sightseeing. This is not good for any gear, maybe the fact that the transmission dampers where stone hard has also something to do with that.

will be continued,

Jensen

[supersports400]

update 30-03-2010

examination of parts, part II :

All shift forks where in perfect condition, all measurements where within specifications, and the surfaces looked like they never touched anything. The bores on every shift fork where as new.
The gearbox never gave any problem, so I didn't expect any issues related to the parts of the selector group.

The shift drum was very nice, especially the "bends" in the groove. I've seen a lot of damaged drums, always look at the places, as pictured. The side play with the pin on the shift fork was as new, again, no signs of damage at all. I checked everything and couldn't find anything what give away the fact that it did the job 65.000 miles.

The shift fork shaft was another story, it is bend, not much, but it ain't straight, although it is within specifications I decided to replace it, especially because of the fact that the surface wasn't very nice anymore too. It's difficult to see in the picture, but if the shaft was straight, no light would come through the flat surface and the shaft itself.

The shift shaft itself is in used condition, There is some wear at the point where the shaft comes through the case, but this is within specification. The shaft is straight.

All other small parts where as perfect as can be, and no further action is required. I bought the shaft already a few years back, because I knew that this would be a risk part. I'm still looking for a nice low miles transmission, to transplant it in these cases,

Jensen

[fastbroshi]

Wow that is odd that the gears would be in such bad shape and the forks and shift drum would say otherwise.  Like you were alluding to, must've had to do with his riding style.

[supersports400]

update 30-03-2010

examination of parts, part III :

The last important part is the crank. I decided to measure the crank with plastiguage for a quick and dirty check on the bearings and crank condition, but before measuring I had to clean the crankcase surfaces.

First remove crank bearings after cleaning the surface and marking with a permanent marker.

First I clean the empty cases in engine cleaner, and after drying I start to scrap the old packing material from the surfaces. I use a self made tool for that (picture 1 and 2).

After removing the packing material with this tool, I take a wet stone to remove small pieces from the mating surfaces. This must be done with care, you don't want to ruin a otherwise perfect mating surface.
Never use the wetsone dry, always use petrol or something like that. Never use the wet stone balancing one one surface, the change that you destroying the surface by rounding it is big. Always place the wetstone on at least to points on the mating surface, don't apply much power, but wipe it gently but straight over the mating surfaces (picture 3).

After this work (it takes a few hours) clean the engine cases good, because every part of dirt on the cases can mislead the measurement. Working with plastiguage is easy, nice and accurate, but only when everything is clean.

Put the bearings back in there places, put in the crank (dry and cleaned) put plastiguage on the bearing surfaces and place both crank half's together (don't put the plastiguage under the crank, the weight of the crank will interfere the measurement).

Now put the eight special crank bearing bolts into place (cleaned and lubricated with molycote) and torque them to specifications and in the right order. Wait a few seconds, and get the bolts out (in the right order, and remove the crankcase half gently.

The only thing you have to do is reading the play directly.

My crank (main) bearings where 0.042, 0.045, 0.042, 0.042, 0.045. All, except nr. 2 and 5 are within build-in the specification (new), and that, as you can imagine was a great relieve, nothing to renew here.

Jensen

[supersports400]

The crank itself is very, very nice, there are no signs of wear, not on the bearings too, all perfect. (pictured with the plastiguage on it).