Topic: Stuck cam chain adjustment nut/screw (1978 CB550 K4)

[ReggieC]

Hi everyone,
I recently bought a 1978 CB550 that sat for a very long time, the odometer shows only 5,500 miles. I've cleaned out the carbs, set the timing, and adjusted the valve clearances, and then engine runs OK.
Now trying to adjust the cam chain tension, but the lock nut and screw are stuck together (maybe rusted together?). I can loosen the lock nut, but the adjusting screw moves with the lock nut.
I've used penetrating oil, let it sit overnight, and then a butane torch on the nut and screw, but they won't break free of each other.
Any suggestions on how to un-stick this nut and screw? 
Thanks!

[TwoTired]

For me, the best penetrating lube is a 50/50 mix of acetone and automatic transmission fluid.

Have you studied how the mechanism works?

Does the post still have the slot in the end?

[ReggieC]

Hi TwoTired,

Thanks.  Yes, the adjusting screw still has the slot on the end (but it's a bit chewed up by the previous owner). I know that the screw goes into a sprung rack and pinion mechanism, but I have not looked if the mechanism is stuck, or if the gears are engaged.

[bryanj]

The gears are always engaged unless broken by a gorrila twisting the screw too much which, unfortunately, sounds like your PO!
Sounds like the end of the screw thread may be "mushroomed" you could try tightening up the nut and carefully filing the end of the thread.
Also unfortunately head has to come off to remove tensioner assembly and sometimes barrells lifted as well, plus its an expensive part to replace

[ReggieC]

The gears are always engaged unless broken by a gorrila twisting the screw too much which, unfortunately, sounds like your PO!
Sounds like the end of the screw thread may be "mushroomed" you could try tightening up the nut and carefully filing the end of the thread.
Also unfortunately head has to come off to remove tensioner assembly and sometimes barrells lifted as well, plus its an expensive part to replace

Owch.  I was hoping that this was not the case.   

[Deltarider]

It's the most crappiest part of the engine. If it lasts 50.000 km, you're lucky.

[bryanj]

They work fine until you get an owner insisting on putting a screwdriver in the slot and forcing the tensioner because he either dont understand how it works or dont care

[Little_Phil]

Now trying to adjust the cam chain tension, but the lock nut and screw are stuck together (maybe rusted together?). I can loosen the lock nut, but the adjusting screw moves with the lock nut.

The adjusting screw (the bit with the slot) should on no account be turned by external force. It must be held still by a driver in the slot. Letting the screw turn may damage the crude internal gear.

[Deltarider]

They work fine until you get an owner insisting on putting a screwdriver in the slot and forcing the tensioner because he either dont understand how it works or dont care

You repeat this over again and again, but I know for a fact Dutch Honda mecs have received instructions on this by the importer: Honda The Netherlands. They would meet once a year for education. So there's nothing to boast of as amateurs like most of us didn't receive these ins and outs. Trying to replace the locking nut can be enough to damage the whole thing because almost every bolt has mushroomed over time, once you've had a screwdriver on that bolt. But maybe you can show us how you can lift the head without having to turn that bolt. Question is why didn't Honda do it right? The CB350/400 tensioner was also bad. Later more modern Honda's had it right. Why couldn't Honda do it right the first time? And if you know someone who managed to do more than 50.000km I'd like to meet him. Be fair.

[Deltarider]

The adjusting screw (the bit with the slot) should on no account be turned by external force. It must be held still by a driver in the slot.

But 'holding still' can be enough to mushroom that bolt and then you have a problem. Don't ask me how I know. That's why I maintain it's poorly designed. Honda never expected their bikes to live that long. Realise that in those years in the Japanese consumer market a vehicle of three, four years was considered old. Japan has exported literaly shiploads and shiploads of secondhand cars to Ireland.
http://forums.sohc4.net/index.php/topic,185790.msg2152622.html#msg2152622

[bryanj]

Delta, UK Honda told me what i repeat and i have seen a lot of the mechanisms where the body of the adjuster mech has been spread so much that the gear no longer meshes with the rack and the only way that can happen is forcing the stud gear, you dont mushroom the slot if you use the correct size screwdriver BUT if sevicing is carried out correctly and at correct times there is no need to ever use a screwdriver.
The Honda uk team admitted that the factory got it wrong in saying adjust with engine running and came up with the idea of putting tension into the front run, loosening and retightening but decided it was too difficult for the average owner to understand so it was never in a manual, just word of mouth one tech to the next

[Deltarider]

Delta, UK Honda told me what i repeat

That was more or less my point.
I admit I wasn't concentrated the last time I was at it, when I only wanted to replace the somewhat rounded locking nut for a new one. Before I realised the nut wasn't coming any further towards the end of the bolt, the damage was already done. Nut and bolt had turned. Although I managed to quiet the chain, having to run the engine now, I don't know what the situation inside is. All I know is the method by the book now doesn't work anymore. Maybe someone has a suggestion for something I could try before having to open the engine.
I'm not criticising you for repeating your warnings but my point was: it doesn't take a gorilla to have the @#%$$! thing damaged. When even I who was well aware and in the past has been warned by mecs, in spite of that, has this happening, the tensioner is just too fragile. I don't know if I can try to fiddle a bit from the outside without having to open the engine. I'm open for suggestions.