Topic: I #$%*ed up. . now what -- '75 CB400F

[Joshrma]

I've owned my '75 cb400f, and kept it ticking for almost 20 years. At the end of last season I had the cam chain tensioner fail on a ride and put another 1-2 hundred miles on it before I understood what had happened, replaced it and did my best to flush the metal debris out of the sump.
While it's undetectable at idle, I noticed a hint of oil smoke in the exhaust, so all that free metal did some damage before I noticed.
between that and what I think is the dreaded primary chain rattle, I know that a tear-down is in the near future. The question is, am I likely to make anything worse by continuing to ride it for the rest of the season?

[MauiK3]

I'll say yes, these things tend to get worse if kept in service with similar problems. The big thing is what are you doing to the crank bearings and every other bearing.

[newday777]

Hey Josh
Edit your title to include that this is on the 400F to possibly get more replies from those that know the 400F.
You didn't say, did you pull the oil pan off and clean it out along with the pickup screen to get the debris out?

[calj737]

If you are only detecting a “hint” of smoke, I’d say you’re fine. Did damage occur? Perhaps. Is it likely to be catastrophic after a repair? Not likely.

It’s possible the smoke was always there or after your repair you didn’t get the valves adjusted properly. Does the smoke occur at idle or when riding? Is it worse on startup after a cold sit?

Best you can, provide as much specifics about the smoke, color of it, and when it occurs. That’s the easiest way to diagnose the root cause and repair.

[Joshrma]

I noticed the smoke when I was warming the bike up on the stand to balance the carbs.  The valve clearances and cam chain were tensioned when I replaced the tensioner.  It's white, and faint enough that it took me a minute to be sure it was oil smoke rather than water condensation (it was a humid, rainy day, so water in the exhaust was my first hope.)
It had been idling long enough that I'd expect leak-down from valve seals would have been burnt off, so I suspect the rings.
Realizing that I hadn't dodged the bullet after all, I shut it down and haven't had time or place of mind to continue without some further advice.

newday777: I didn't drop the pan/clean the screen at the time. -- That was on the roster for the end of the season when I investigate what I suspect is the song of an overdue primary chain.

[BenelliSEI]

I assume you changed the oil and filter? Did you look deep in the folds of the filter and spot any debris?

[Joshrma]

Yes, I changed the oil and filter put a couple miles on it and changed them both again. The oil was clean on the second change. I opened up the most recent filter and read it like a book: the oil had less than 100 miles on it, so it was still clean amber. and I found maybe a dozen or fewer tiny flecks total caught in the folds.
What I don't understand is how much additional damage I'm doing once the sump and new oil are clean and the filter is doing it's job: How much of the debris that comes in contact with moving parts gets trapped there and continues to do damage rather than abrade before washing away, as god and Standard Oil intended.

[Mark1976]

   What's the bikes mileage?

[bryanj]

Dont forget unfiltered oil splashes round all the gearbox/primary bearings plus primary and camchain links and whilst fitered oil goes to crank and cam bearings particles could splash externaly onto the surfaces.
When you KNOW you have a problem its best to fix it sooner than take a risk.
Primary chain use a Kawasaki one its cheaper, dampers in primary hub expensive but change them, there is a tensioner pinch bolt repair kit from knocksnrattles in uk, if they wont post direct i will act as middle man for you.
Dave Silver does an alloy horseshoe replacement made by a well known south african uk member

[MRieck]

The 400F does not have seals on the exhaust guides...oil getting past there will cause smoke on start up.

[Joshrma]

The ODO says 32K/mi (16k from me. Can't swear that previous 16k is accurate, but seems likely)

bryanj, thanks for the notes on the tensioner and primary chain. -- One of the things that I've learned is that the tensioner pivot/arm are operating correctly.
Will check out the Kawa chain. I'd been daydreaming about a breakable link primary that would save me the misery of breaking the case, which is more than I'd attempt in my shambles of a workshop right now.

[Mark1976]

The ODO says 32K/mi (16k from me. Can't swear that previous 16k is accurate, but seems likely)

bryanj, thanks for the notes on the tensioner and primary chain. -- One of the things that I've learned is that the tensioner pivot/arm are operating correctly.
Will check out the Kawa chain. I'd been daydreaming about a breakable link primary that would save me the misery of breaking the case, which is more than I'd attempt in my shambles of a workshop right now.

   At nearly 50 yrs old and 32k on the clock, yer getting up there. If it didn't smoke a little at idle, then I'd have been surprised. The primary dampers are as hard as a newly wed on his honeymoon, and the primary chain is in the tired phase of its life (just my opinion). I've only seen one with more mileage (38k), it ran fine but it was noisey and a bit sloppy shifting.
   Bite the bullet split the bottom end and replace what ever needs replacing, and if you've driven for any period of time with a loose cam chain, as loose as it sounds, then adjuster pivot definitely sustained a little bit of gouging from the chain (one of the reasons cam chain adj's stick). What do you have to lose. Just something to think about, your bike...

[Tim2005]

At 32k miles the stock primary chain should have loads of life left, mine's on over 80k. The noise from it is more likely due to the engine needing a good service & then having the carbs balanced.

Also I'm thinking it is unlikely there's a connection between camchain issues and oil smoke, but I'm curious as to finding out what way the the tensioner failed, as that's not very common either

[Joshrma]

You caught me on this one: I mistook an irregular rattle/stumble at idle for the cam chain and managed to over-tighten the cam chain, which then wore through the rubber, and within a minute or two chewed through the sheet metal backing of the tensioner spring, which celebrated by throwing a glitter party in my sump. That's the connection to the cam chain.
It would be nice to discover that the primary chain was fine. -- I'll know when I drop the sump. Maybe fortune will smile upon me and the idle will smooth out when I do balance the carbs.

[bryanj]

This screenshot is from a uk supplier but the part number will be the same.
Fits 400, 500, 550 and 650 four Hondas

[HondaMan]

There's quite a few (inordinately so, by population) CB400F bikes here in the Colorado Front Range area: they are popular as canyon racers. They also have LOTS of miles on them, like 60k is very common, and more, still in OEM shape (in the engines). It's a fine engine, inherited all of Honda's (customer abuse type) experience with the 550/250F/350F series bikes. It's also a pretty tough engine.

It does tend to sound like it's about to grenade when it is running unevenly, and I have noticed that is when they also smoke. Getting the timing right and the carbs synched goes a long way toward removing that symptom. The symptoms may be more like it's 'bark' than the 'bite' caused by ground-off grit from the tensioner backer strip.

If you take it apart, don't change the piston rings unless you do a full rebore with new oversize pistons (and come back here for proper advice on that topic, it is VERY easy to do the Baby Fours wrong). Chances are mighty slim that this grit did any severe damage to the bores in the short time it's been thru this engine, due to your diligence in chasing it out. The oil filter kept it out of the bearings, catching it in the filter for you.

[Ozzybud]

Don't forget the Clutch Basket Rattle notorious on the CB400F's
When I bought my 400F last year it sounded like a bag of bones when running. Replacing the Rubbers made the bike sing again. It had 20k on the clock

[Killer Canary]

There's quite a few (inordinately so, by population) CB400F bikes here in the Colorado Front Range area: they are popular as canyon racers. They also have LOTS of miles on them, like 60k is very common, and more, still in OEM shape (in the engines). It's a fine engine, inherited all of Honda's (customer abuse type) experience with the 550/250F/350F series bikes. It's also a pretty tough engine.

It does tend to sound like it's about to grenade when it is running unevenly, and I have noticed that is when they also smoke. Getting the timing right and the carbs synched goes a long way toward removing that symptom. The symptoms may be more like it's 'bark' than the 'bite' caused by ground-off grit from the tensioner backer strip.

If you take it apart, don't change the piston rings unless you do a full rebore with new oversize pistons (and come back here for proper advice on that topic, it is VERY easy to do the Baby Fours wrong). Chances are mighty slim that this grit did any severe damage to the bores in the short time it's been thru this engine, due to your diligence in chasing it out. The oil filter kept it out of the bearings, catching it in the filter for you.

250F?
Please tell me that' wasn't a typo.
I'm intrigued.
Is there such a thing?

[HondaMan]

There's quite a few (inordinately so, by population) CB400F bikes here in the Colorado Front Range area: they are popular as canyon racers. They also have LOTS of miles on them, like 60k is very common, and more, still in OEM shape (in the engines). It's a fine engine, inherited all of Honda's (customer abuse type) experience with the 550/250F/350F series bikes. It's also a pretty tough engine.

It does tend to sound like it's about to grenade when it is running unevenly, and I have noticed that is when they also smoke. Getting the timing right and the carbs synched goes a long way toward removing that symptom. The symptoms may be more like it's 'bark' than the 'bite' caused by ground-off grit from the tensioner backer strip.

If you take it apart, don't change the piston rings unless you do a full rebore with new oversize pistons (and come back here for proper advice on that topic, it is VERY easy to do the Baby Fours wrong). Chances are mighty slim that this grit did any severe damage to the bores in the short time it's been thru this engine, due to your diligence in chasing it out. The oil filter kept it out of the bearings, catching it in the filter for you.

250F?
Please tell me that' wasn't a typo.
I'm intrigued.
Is there such a thing?

Oh, yeah!
In Japan their was a lot of response to Honda about having an SOHC4, because restrictions (in the 1970s, don't know about today) on engine sizes and bike weights in Japan were very strict. Sochiro heard the requests, as he was a 'man of the people' sort of business guy, so he had Honda make a 250cc version of the 350F. It has even smaller carbs on it, had 4-4 pipes, and outwardly was very hard to tell from the 350F. Their vehicular restrictions on motorcycles drew a 'line' at 250cc as being the largest allowed motorcycle in many of their larger cities unless you had special permission from their government or training (like being a cop) because their air pollution was the worst in the world (outside of Mexico City then) and bigger bikes (or cars) were simply restricted.

I never knew of it myself until 1999 when a local guy approached me here with a 250cc version of the engine, because he thought it was another 350cc and his was in rough shape: when he started to attempt an engine swap he discovered it as clearly stamped as "CB250E-....". When he asked me about it, I was stumped: since then I've seen several of them. They make all of 17 HP at 10,500 RPM, top speed of 78 MPH. Since Japan's top hiway speed (then) was 50-something MPH, that wasn't even a touring restriction for them!

[Killer Canary]

Very enlightening; thank you.
I have to research  the CB250F now.
I hope there's something out there.

[Joshrma]

Don't forget the Clutch Basket Rattle notorious on the CB400F's
When I bought my 400F last year it sounded like a bag of bones when running. Replacing the Rubbers made the bike sing again. It had 20k on the clock - Ozzybud

Thanks for the reassuring words. . . the clutch certainly weighs enough to make some terrifying noises. I don't see any rubber parts on the parts fiche or resale lists, so I'm not sure what you're referring to.
My clutch effort is distressingly high, despite new cable and proper routing.

[bryanj]

The clutch cush rubbers were not available seperately from Honda but there are some out there on ebay BUT there are 2 different sorts and you cant be certain which you have till you take it to bits

[bryanj]

Two screenshots of a UK supplier