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Lord Gruntfuttock's 1973 Honda Trail 90 (CT90)

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Lockdown update. Wheeled this out of the shed of despair and found the rings and valve stem seal I'd bought to see if I could fix the plug oiling up issue...

Exhaust valve cover was full of oil, interestingly...

And all came apart ok, I'd used antisieze on the bits I had had off previously...


No valve spring compressor, but my lockdown method worked beaut, clamped head to bench and levered valve down with open ended spanner, smaller spanner was just a spacer for leverage...

Cleaned and lapped valves...

And cleaned all bits in my 'new' parts cleaner, that I've had for months...

And reassembled valves, new blue viton seal in the foreground...

 I did find an old seal but not sure where it came from, think it may have been wrongly installed on the intake...?

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Also found this, one broken compression ring...


but bore looked good, and I had a set of standard rings so cleaned piston and installed them. Also masked cylinder and painted it after removing old gaskets...

and gave it a quick hone before hone disintegrated...

And cleaned 46 yr old gaskets off...

And that's pretty much where things stopped as the gasket sets I had were for the wrong thing. Ordered another set which should be here in a couple of days (being essential) so did the only other thing I could do, added some stickers to the plastics...

So shame I can't put it back together today, but made some good progress and hopeful it'll make a difference when all done... :)


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Gasket set arrived today, so cleaned things up and slid the barrel on. I had re-honed this yesterday with my bodged together hone (glued one stone back on)...

Was bloody tricky getting the rings in but got there. Added rest of top end hardware ready for setting valve clearances, points, timing etc...

But main thing is it's all buttoned up, hate leaving engines open. Would have made much more progress if also wasn't working from home...

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Made some progress yesterday. Fitted cam, valves etc, torqued things up and set plug gap, points gap, timing and valve clearances, and tried to start it. Had spark so thought it's be easy. Nope, kicked and kicked and kicked till I was a sweaty mess without even the slightest cough. Was wondering if timing was 180 degs out, then checked spark again and very weak, so had a think...

That's right, these things need a good battery to start, checked and 4V. Doh...
Chucked it on charge and decided to drain the old fuel for good measure, plus a new plug. Barried up another battery and was rewarded with a fat spark, so tried it out and she burst into life...

Went for a quick hoon up the road but underestimated how useless the old 6v lamp is, especially when it's pointing at the sky. No moon out and no streetlights so was almost completely blind. Thought it best to park up for the night... :)

Lunchtime today checked the battery, had risen to 6V but drained to 4v almost immediately so wired in the spare battery I had temporarily connected. Burst into life almost immediately so quickly threw the covers on and some extra fuel into her...

And went for a much less scary hoon, seemed to go alright but was only round the block so no real test. Look forward to a better run when I can see how it goes over a distance. Looks good with the stickers though...

Seems to have almost the same top speed in 3rd or 4th, not sure if gearing would fix that, didn't have gps running but seemed to be around 80kmh. Did a compression test when back and it's around the same as before I did rings, an acceptable 158'ish psi...

So overall a win, lockdown plug chop here we come...


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Fitted my Ali rear light yesterday, so junk, but cost around $15 so hope it'll last for certification process...

I used the original rear guard bracket to mount it on, but it is so cheap/flimsy (chromed plastic) that one of the screws vibrated out on my first test run, will look at mounting it better on rubber isolators so it stays put...

And did some speed runs, 1st, 2nd, 3rd all good then when I knock her into top (at around 74kph) it either stays there or actually slows down, unless there is a kind tail wind or slight downhill. If I get a good bit of road it comes on song and actually winds out to 100kph...
[proof] :)

So looked at gearing options, standard is 15 front and 45 rear, and consensus is that's not bad for all round riding, apart from high speed runs, which it was never built for. If I change rear sprocket for more speed I already know it won't have the grunt to push it, and gearing it down so it pulls in 4th will make 1st gear redundant. Think i'll just leave it as Mr Honda intended.

And it starts on choke easy but you have to flick choke off almost imediately, plug looked a good tan colour too, but have only been round the block so will check after a longer, hotter run. Looking ahead at cert process, need to sort brake lamp and indicators, but 90% there. Would love to get this legal, have started the process so be interesting to see how things go... 

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Need a mirror so I can see if I'm being followed on my speed runs (paranoid about being oblivious to cop behind me while I've got my nose on the speedo and butt crack exposed attempting land-speed record) - so pulled one off the CB360 in the shed. Factory Honda item and free, but had a 10mm thread so bought a couple of adapters on trademe. Seller sent me the wrong ones though, and doesn't have any more, so looked at Barrying up an adapter, then realised there was heaps of meat on the mirror mount, so just drilled/tapped it out...

And looks bloody good cleaned up and installed, considering it was a rusty old bit I was going to discard...

Since I'm going to try to register this keeping things factory looking (apart from rorty exhaust :)) can only help...

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On 30/04/2020 at 23:25, Dolan said:


Mate ya lived til you’ve binned a Honda ct/cub and winded yourself whilst trapped underneath

Jeez I haven’t been winded in a long while, maybe I should get a ct

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  • 2 months later...

Do you have a picture of where those bars attach at the bottom?

On saturday I came I to possession of a ct90 K0. (Apparently they're rare/oldschool/desirable/I'm new to CTs so I dont know) but those bars arent there. 

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  • 6 months later...

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