Topic: 75 cb400f cam chain tensioner bolt broke off

[cmorgan47]

while trying to adjust the cam chain, the bolt broke off maybe 3 threads into the crank case.


ideas on removal?
safe to ride? [edit] yeah, i know[/edit]

[GroovieGhoulie]

Uh-oh.

You can possibly carefully retrieve it using an easy-out, but most likely you will need to drill it out then repair the threads using an insert or alloy welding and machinnig, an expensive proposition.

Sorry man, that's an expensive repair.

[JHansen]

Same thing happened on my first 400. Only I didn't do it, I bought it that way not realizing what a serious chink the cam chain was in this motor anyway.

SinceI pulled the motor out of the bike for a rebuild, the machine shop drilled out the old broken bolt and helicoiled the hole to fit a new adjuster bolt. Motor has been running for 500 miles now with no problems.

If you are good with helicoil you MAY be able to pull off the same thing, but man I'd HATE to try it with the mill in the frame, I have my doubts you can get to it well enought to do effective work.

You know what... hold on a sec...

OK, I'm back, had to run to the garage to look at mine... You might be able to get it done without pulling the motor. You'll def. have to yank your header though.

Let us know how it goes, good luck... and you never know, that busted bolt may be a cry from the motor for rebuild anyway!

John

[supersport_CB400F]

Sell the bike and buy another bike with a good bolt.....then be careful what your doing with that adjuster bolt  Why did you take it out 

[Short Round]

Take the bike to any car or motorcycle place and they ahould be able to help getting it out.  I had a head gasket bolt on an old car break off and a guy got it out for me.  Then all you have to do is find a new colt to replace it.  Remember when the get it out you wont be able to rid eit hyome unless you  have the new bold with you and can adjust the tensioner at the shop.

[3 sticks]

Sell the bike and buy another bike with a good bolt.....then be careful what your doing with that adjuster bolt  Why did you take it out 

Yeah the bikes pretty much toast, whitch means you should sell me your pegs and linkages for my 77' 

My two cents are your best bet being bringing the bike to a shop that could get it out UNLESS you think you have the machining skills to do it yourself. I just think bringing it to a shop would be an easier process; even if you know how to do it yourself. That stuff can be pretty annoying...

cheers; will

[cmorgan47]

having mulled it over for the evening, i was really thinking the worst case was drill/tap.  is that not an option?

first i was going to try heat/easy out, but if that didn't work, pull the engine and have it drilled & tapped.

thoughts?  what am i missing there?

[edit]

Why did you take it out 

i didn't.  i was trying to tighten it a bit as--now that i have it idling where it should be--i could hear the chain rattling around like crazy.

[bryanj]

With the exhausts and front engine mount plates off, plus as i remember it the front wheel and fender out, you can just about get in to drill and helicoil BUT its tight and very awkward to do. The best way is to pull the motor and drop the lower case then take that into a decent machine shop that can drill and coil it for you. The bolt is just a "standard" 6mm set bolt BUT you must remove the threads at the end that clamps the adjuster as the bolt will "mushroom" when you tighten uo and you will never get it out again if you dont!.

[supersport_CB400F]

The bolt is just a "standard" 6mm set bolt BUT you must remove the threads at the end that clamps the adjuster as the bolt will "mushroom" when you tighten uo and you will never get it out again if you dont!.

It's not a standard 6mm bolt B ...it's a two thread bolt with different threads one for the adjuster and one for the lock nut and a O ring 

[crazypj]

If chain is still loose you may get away with a small diameter drift on the end of adjuster.(10mm head, 12? mm threaded plug) Tap it down to tighten up a bit. If the lock bolt has snapped before locking the adjuster you have to get it fixed first. This works even if you dont have a broken bolt, problem is, if you overtighten you have no method of backing off (the pivot on 'horseshoe' is usually messed up on 400 so they almost allways need some 'help')
PJ

[cmorgan47]

ok, looking at the parts manual, there's the bolt, a lock nut, a washer, and an o ring.

the lock nut, and i presume the washer are on the outside, where is the oring? 

the bolt seems to have broken on the thicker outside part(for the locknut).  does the smaller thread actually go into the tensioner?  from the manual it looked like it just pressed up against it.


the few suggestions for what to do once i get it out (assuming i can) are to use a heliocoil, but wouldn't tapping it be better?  not afraid to pull the engine to do so.  wouldn't be the first.

[edit]
ok, i think i see now..... does the smaller thread go into the horseshoe?

[supersport_CB400F]

If you can cut a groove in the snapped bolt you can use a screwdrive too get it out, then just buy a new bolt….if you start using a drill then you may bugger the threads then you may have problems.

[cmorgan47]

If you can cut a groove in the snapped bolt you can use a screwdrive too get it out, then just buy a new bolt….if you start using a drill then you may bugger the threads then you may have problems.

that's the plan.  first try to back it out with liquid wrench, heat and "easy outs"  then when that inevitably fails, if need be, drill it out and rethread with a tap set. 

[crazypj]

Not that I remember. the small thread goes into the crankcase and presses on the adjuster rod to lock it in position. the large thread is for the locknut only. The 'o' ring sits in a recess in crankcase between the two threads. (if you have Haynes manual its page 21)  Remove the plug from top of spring/pushrod and see if you can push pushrod down a bit, that bends the blade (part 4) to tighten chain. the pushrod is only aboutt 6mm dia but plug is 12mm(I think) so you need to use a small diameter bar to push on.
 Last time I did one of these was 1988
PJ

[supersport_CB400F]

If you can cut a groove in the snapped bolt you can use a screwdrive too get it out, then just buy a new bolt….if you start using a drill then you may bugger the threads then you may have problems.

that's the plan.  first try to back it out with liquid wrench, heat and "easy outs"  then when that inevitably fails, if need be, drill it out and rethread with a tap set. 

Sell it 

[cmorgan47]

the small thread goes into the crankcase and presses on the adjuster rod to lock it in position. the large thread is for the locknut only. The 'o' ring sits in a recess in crankcase between the two threads

got ya.  so only the large thread isn't gripping into the crankcase at all, just the small one.  and the end just pushes on the tensioner....like i originally though.

don't have the haynes.  the honda service and parts manuals.

Sell it 

no way.....i'll buy a new engine first.

[supersport_CB400F]

Sell it 

no way.....i'll buy a new engine first.

Thats the spirit....the 400 is the best of the SOHC bunch 

[upperlake04]

Thats the spirit....the 400 is the best of the SOHC bunch  Wink

  glad you winked on that one Biffta - otherwise I could have thought you were a 400 snob   Actually saw my first 400 (red) in the flesh yesterday and have to admit it did look pretty nice  - sort of.. 

[bryanj]

OK the original is a special BUT a straight 6mm will do the job with a 6mm nut and washer as a lock. The bolt, if broken, is bound to be siezed in the casing or why did it break?

[supersport_CB400F]

Thats the spirit....the 400 is the best of the SOHC bunch  Wink

  glad you winked on that one Biffta - otherwise I could have thought you were a 400 snob   Actually saw my first 400 (red) in the flesh yesterday and have to admit it did look pretty nice  - sort of.. 

I’m always tongue in cheek UL  and I comment on any bike if I’ve been and done that and lots of issues are across the whole range of SOHC bikesso I do if I can …I’m never a 400 snob just a 400 sort of guy, glad you saw one and thought it was worth a smile 

[cmorgan47]

ok, having run this by a buddy of mine who i trust on the topic, i have 2 questions:

if i pull the bolt all the way out, will the tensioner fall apart in the crankcase?
is it safe to run?  not leaking oil, seems like the bolt is just sitting right where it was.  this was brought up because he suggested i ride it to his place (a couple of miles) and try the easyouts....something he's pretty hopefull of, as he's done it a few times.

…I’m never a 400 snob

me either, but i love this bike.  i've put a bit into it, and think it'll be fine again.

[supersport_CB400F]

Whip it out if you can and it wont do any harm at all  but lock it with a bolt before you ride again 

[supersport_CB400F]

Don’t snap the ezee-out in the bolt or the drill option is gone those things don’t like drills once they break

[cmorgan47]

Don’t snap the ezee-out in the bolt or the drill option is gone those things don’t like drills once they break

good advice.

also, a friend of mine just checked it out and gave it a quick spin around the neighborhood.  like i said, no oil leaks, no (new) weird noises, seems to run ok......might ride it gently for a day and see.  i was planning on a teardown this fall anyways.
[edit]
oh, and i just aquired a 72ish cb550f....ran 15 years ago, hasn't tried since, free..... no title though.

[Bodi]

There's not any oil pressure behind the bolt, and not much oil is going to make it up the tensioner shaft and past the threads.
Removing this locking bolt just makes the tensioner free, nothing will fall apart.
Don't run the engine without the lock bolt though, the cam chain will go very slack and can damage the tensioner pivot making the tensioner inoperable. The chain may even chew through the case into the main oil gallery (very bad) but I've never seen this happen and don't know if it's an issue with the 400.
I would say if you have a fairly quiet chain, just leave it until you tear down the engine. The possibility exists that it will work its way loose and the cam chain will suddenly be able to go slack.
I have seen a modified 400F with a pusher bolt installed where the cap screw on the spring shaft hole is. Used carefully this looks like a better and more positive adjustment than the original system. With the engine running, one could snug down this bolt - pressing the adjuster shaft down - and lock it down as soon as the chain stops its infernal rattling.

[cmorgan47]

bodi, good info, thanks.

the lock nut is the part that broke off....right where it begins to taper.  the tensioner bolt never moved.  is there a chance that it will work its way loose due to engine vibration?

[bryanj]

Probably it wont work loose, as if the bolt snapped it must be siezed in there

[cmorgan47]

yeah, i rode it around a bit last night without incident (except that the #1 cable on my new coil is a little short so it popped out and freaked me out when i saw a blue glow by my knee), so rode it into work today.  it's not going anywhere.  (the bolt, not the bike)

the only worry is that i can't adjust the camchain now, but plan to swap it at the end of the season anyways so i'll take care of this then.