Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: SeanFD on December 25, 2023, 01:45:36 PM
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Hi all, Happy Christmas.
With nothing else to do before dinner this afternoon, i decided to use the time to try, finally to get my 400F2 running; yes the same one I started resurrecting during the pandemic.
Anyway, I sorted some minor electrical problems and power was getting to where it was supposed to be (and when). Even thought the battery voltage had fallen to 12,4 or thereabouts, I decided to try and start it up.
It coughed once on the kick start and then nothing. I tried it on the started and then I was hit on the head by the air filter cover.
Here I stopped, as dinner was nearly ready, and I wasn't sure exactly what this meant.
Can anyone explain and advise whether it is safe to try again with a fully charged battery, or have I done something seriously wrong in the rebuild?
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You can get a intake "backfire" in a healthy engine with build up of fuel vapour while trying to start a reluctant engine. Possibly not much wrong.
But, if there’s more common confusion in ignition system on these engine, coils connected to wrong plugs or points firing the wrong coil when inlet valve can be open, when it'll do it more easily.
Assuming no obvious mechanical conflict, then check carefully the ignition wire routing etc against manual to see if there's anything obviously wrong.
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I agree check the timing/ firing order reads like a back fire.
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Good call guys, that's exactly what the problem was; I had attached leads to wrong plugs. :-[
But now something is DEFINITELY WRONG!
Started on first press of the switch and ran quite sweetly. Stopped and started again, and then:
https://youtu.be/c-6r2hDONYw (https://youtu.be/c-6r2hDONYw)
Now the motor won't turn over with either the starter of the kickstart :( :(
The oil pressure light went out almost at once and I can see there is oil up at the valves, so my thought is that it is related to the cam chain rather than a seized piston. I can rock the crank a few degrees using the nut on the points end but nothing more.
HELP, please! And be gentle with the bad news.
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As it happened so quickly, I would say something has snapped or jammed.
Edit..... Also, if you've got oil to the cam, that doesn't mean it's not a seized piston. The oil to the top end comes up a different oilway.
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If it stopped suddenly and will not turn over possibly cam chain broken or something fell off internaly and jammed the cam/crank
DO NOT rotate the enging with the big nut on the advancer unless plugs are out, also do not rotate the crank till you have sorted what happened or you may bend valve(s)
Remove cam cover and inspect, my personal ideas would be cam sprocket bolt fell out or cam chain snapped
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Cam sprocket bolt came out, somehow dislodged the left rear dowel, which got jammed between the chain and body.
This is where the dowel ended up:
[attach=1]
This is where the bolt ended up:
[attach=2]
And this is what they looked like:
[attach=3]
The only other damage I can see is this:
[attach=4]
[attach=5]
So it looks as of I might have escaped lightly. The one question I have now is what has happened to the rest of the dowel. if this has dropped down teh cam chain tunnel, will it be safe to run the engine? Is there anywhere else it could have gone?
There is what looks like a large washer - can't think of another way to describe this - on the camshaft sprocket, which is held to the sprocket by the bolts. it looks as if it has been bent but I cannot find it on the parts fiche. will it be OK to simply put this back in place and bolt it back to the sprocket? To replace it would require removing the camshaft.
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I can see how the bolt came out if you didn't put locktite on it but I can't fathom out how the dowel got involved in the failure 🤔🤔🤔
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If you mean the big wide disc shown in my photo, it doesn't show on the fiché but they were fitted to the late F2 models, earlier models didn't have them. You appear to have a lot of scoring on the camshaft.
[attachimg=1]
[attachimg=2]
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Yes, I saw that on the photo also, although I didn't notice it on the shaft itself. I'll have a look at it in the morning. I'm (almost) sure I put lactate on the bolt, but maybe not.
And the dowel puzzled me too. I'm assuming that is what it is because it is missing :-\
I was referring to the disc. If it is not on the fiche, how can I order a new one, assuming it is available?
So is it OK to turn over the engine now to see if the remains of the dowel have fallen through, or are lodged somewhere?
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You need to remove the sump pan to see if it ended up in there before trying to turn the engine over.
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The dowel must have been dislodged when you put the cover on, if some models do not have the big washer, which i havent seen but then never stripped an F2, it should be ok to run without.
Yes pull the sump to check on bits and i would fit 2 new cam sprocket bolts plus check threads in cam for damage.
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I will do.
DSS doesn't re-open until 02 Jan, by which time I'll be back in France – replacing the valves and guides on my K2 – so Rusty's completion gets delayed once again.
For now, I'll just put the covers back, and leave the oil in place till next time.
Maybe I should hire a van :-\ ...
Just for interest, here are a before and after pic.
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I don't think the dowl was dislodged by the cam bolt I think they are two separate incidents. The dowl appears to be a 6mm item and is part of the rocker cover, I think the dowl fell out as you put the rocker cover on and lodged itself in the cam chain tunnel. When you started the engine the cam bolt hit the dislodged dowl and the shock caused the bolt to start undoing itself and fall out especially when you see the damage caused to the dowl and the speed the engine was idling at in the video.
You definitely need to drop the sump to check if the remaining part of the is in there. The sump pan also has a baffle plate and it may have landed on the top of that. It's quite easy to drop the sump, all the bolts are easy to get to with a 1/4” socket.
You could always try fishing down the cam chain tunnel using a long, thin magnet to find the remains. I dropped a head bolt washer down the tunnel once and expected to do a strip but used the magnet method and out it came 👍
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You’ve made a nice job of that 400 on the restoration Sean. I do feel for you with this mechanical failure but you might find a bit of damage limitation in there hopefully. I agree with comments here that dowel must have been dislodged on assembly. Fingers crossed you get sorted soon! You’ll soon find out if you did use loctite when you try and loosen the other bolt on the camshaft sprocket. Good luck!
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That's bad luck Sean - I've generally ensured that the dowels are on the fixed surface first so they can't drop out. It has meant I have had to replace a few as they chewed up a tad on extraction.
As has been said any unaccounted for big lumps should drop down into the sump - goes without saying to change the oil filter. Have you fitted a magnetic dump plug might be worth it as belt & braces.
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I can see how the bolt came out if you didn't put locktite on it but I can't fathom out how the dowel got involved in the failure 🤔🤔🤔
Julie, maybe Loctite is something you recommend, but there's no mention of that in the official Honda CB400F shop manual over in Aladdin's cave.
I built a fair few of those Honda engines during my years in the trade and never had fully tightened cam sprocket bolts come loose.
Bit of bad luck for Sean tho, hope he gets it sorted out.
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I can see how the bolt came out if you didn't put locktite on it but I can't fathom out how the dowel got involved in the failure 🤔🤔🤔
Julie, maybe Loctite is something you recommend, but there's no mention of that in the official Honda CB400F shop manual over in Aladdin's cave.
I built a fair few of those Honda engines during my years in the trade and never had fully tightened cam sprocket bolts come loose.
Bit of bad luck for Sean tho, hope he gets it sorted out.
Indeed you are correct Scoti but if locktite or similar had been applied, it wouldn't have come undone. It's just belt and braces really. It's like the cap / plate that holds the cam chain guide in place at the top, I would advise using locktite on those 2 bolts as well.
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I've never used Loctite on those bolts, so long as they are torqued up they should be fine.
As for the dowel, I tend to locate any dowels in the head rather than in the rocker cover, they shouldn't fall out if they are in the head, as gravity keeps them in place.
TBH I suspect the cam sprocket bolt was never tightened rather than came loose, you tend to fit one but not tighten it, just in case it locks the sprocket out of alignment for the other bolt, spin the engine until the other comes up so you can fit that and then forget you haven't torqued up the first one and move onto something else, anything can cause this, someone speaks to you, a phone call, just something that breaks your concentration, easily done.
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TBH I suspect the cam sprocket bolt was never tightened rather than came loose, you tend to fit one but not tighten it, just in case it locks the sprocket out of alignment for the other bolt, spin the engine until the other comes up so you can fit that and then forget you haven't torqued up the first one and move onto something else, anything can cause this, someone speaks to you, a phone call, just something that breaks your concentration, easily done.
Which is why I prefer to work on my own...
And I adapted the Japanese way: Edding 8750 industrial paint marker...
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So that's why I have yellow dots on my engine bolts to remind me they have been torqued up!
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Yellow paint was used by Honda on the production line for that very reason Ted, it also showed if the owner tampered with the bolts in case of warranty claims.
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Using a magnet, I was able to fish out a couple of additional bits.
Then I turned the motor over slowly - yes Ted, the plugs were out - and all seemed fine.
So now it will have to sit for a while until I get back to Belfast, when amongst the other things, I'll drop the sump, check the strainer and change the filter.
Until then ...
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That's bad luck Sean - I've generally ensured that the dowels are on the fixed surface first so they can't drop out. It has meant I have had to replace a few as they chewed up a tad on extraction.
As has been said any unaccounted for big lumps should drop down into the sump - goes without saying to change the oil filter. Have you fitted a magnetic sump plug might be worth it as belt & braces.