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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 11-01-2012, 08:26 AM   #1 (permalink)
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Unhappy Valve clearance thoughts

Hello
I have just returned from a trip with my Bonnie suffering from an intermittent ignition fault.......see my other thread. I had done a 12000mile (20000km) service a little early before I set off. Bike turned over 20000km while away so I decided to do the valves while waiting for ignition parts. First I checked the clearances, quite an easy procedure. All the inlets were at 0.2 which is the upper limit of the spec. Exhausts were all 0.33 ie plus 0.03. Some say that valve clearances close up over time but this would mean that the exhaust clearances were out of spec from the factory........I dont think so. So do clearances open up, close up or go either way? Also should I adjust to max spec, min spec or in the middle?
Next step........remove the camshafts. I made up two backlash gear locking tools (I have a lathe) and removed the camshaft bearing caps. They were mostly not marked apart from some cryptic markings that meant nothing as far as I could fathom. I marked each one and removed the camshafts. I remembered to pack rags everywhere. BTW yes the torx screws are tight but a good quality torx bit and constant downward force while turning the ratchet does the trip. They give with a crack and then loosen over a couple of turns. Then you can screw them out by hand. I have calculated the shims I need to get clearance at minimum spec........who thinks I should go for max or in the middle..........tell me why.
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Old 11-01-2012, 08:34 AM   #2 (permalink)
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After 20,000 km I would go for minimum. I think the reason why initially the clearance reduces is due to "Valve seat recession". This happens as the head metal compresses a little and the valve seat sinks. I think by now this effect has settled down as the metal "work hardens" and the smaller clearance will give you a long time before you need to reset the clearances again.

Don't take this as Gospel though, better wait for someone with lots of long term experience of these engines (like Mikeinva) to confirm or deny this.

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Old 11-01-2012, 08:48 AM   #3 (permalink)
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Spec is spec but I'd shoot for the middle but not sweat it. Wear from the seat down will give less clearance wear on the top of the stem will give greater clearance (it can mushroom from repeated hammering)
My use of the word wear is subjective.
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Old 11-01-2012, 09:05 AM   #4 (permalink)
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Hello
Good replies.........I just read something interesting. In OHC engines the clearances increase as engine heats up..........In pushrod engines clearances close up as engine heats up. I will aim for min spec. I wonder why my exhaust clearances had opened up, valve seat wear who seem to result in reduced clearance. Indeed if the inlets were set at min or mid spec at the factory they have opened up a bit too. I think there is more going on here than meets the eye.
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Old 11-01-2012, 02:23 PM   #5 (permalink)
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After the first adjustment, the clearances don't move much. I had to adjust 2 valves at 12,000 miles, and they had still not moved at 38,000 miles. So as long as you have them in spec I wouldn't sweat it. I generally aim for the middle of the range when actually changing shims, for absolutely no specific reason at all. If you choose to shoot for one end or the other of the spec, that's fine too.
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Old 11-01-2012, 04:00 PM   #6 (permalink)
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Hello
Thanks for that reply. I will aim for min spec. I have worked out that I need to buy 4 shims........the other 4 shims required I already have. The shims originally fitted were in seven different sizes. I wonder how the factory determines the shims required when they build up the engines? It would seen to be a time consuming and fiddly task if done by hand. Anybody know how they do it?
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Old 11-01-2012, 04:13 PM   #7 (permalink)
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Quote:
Originally Posted by Tasmaniablue View Post
I wonder how the factory determines the shims required when they build up the engines? It would seen to be a time consuming and fiddly task if done by hand. Anybody know how they do it?
With the sort of precision machining available today and close tolerances, I would have thought they require a very small range of shims to start with. Still like to know as well though.

Sometimes the reality is amazing. I remember reading the story told by a Journalist that travelled to the Kawasaki Factory and wanted to know how the 900 crankshaft was trued-up and aligned. That bike had a built-up crank rather than a one piece forged crank.

They took him to a room full of workers armed with V blocks, dial gauges and mallets banging away at the crank webs while hand rotating the cranks and observing the dial gauges...not the high-tech set-up he was expecting.

Last edited by Forchetto; 11-01-2012 at 04:30 PM.
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Old 11-01-2012, 04:58 PM   #8 (permalink)
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they can and will go ether way if the seats wear they get tight.If the cam bearing surfaces wear they get loose.And yes they will check looser hot then cold .Thay is why you need to let the bike cool over night before checking them.I run mine on the tight side but I check mine often.The thight side is quieter.
One time I check the valves after the bike set for 2 hrs then let it sit over night and checked them againthe exhaust valves got .001 inch tighter after setting over night.crazy isnt it but they do that.
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Old 11-02-2012, 02:29 AM   #9 (permalink)
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your exhausts measure 0.03mm over spec.

0.03mm, thats one thou in Her Majesty's Sensible System of weights and measures.

I would not pulling apart the valve train to chase one thou as measuring with feelers does have a certain amount of error, probably in the region of one thou. if it was two thou (0.05mm) thats a different story, I would shim it out

what was the temperature when measured? was the engine still warm or stone cold?

I would leave it for a few thousand kilometers and recheck, chances are it will close up
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Last edited by bonza; 11-02-2012 at 02:33 AM.
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Old 11-02-2012, 05:12 AM   #10 (permalink)
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Quote:
Originally Posted by bonza View Post
your exhausts measure 0.03mm over spec.

0.03mm, thats one thou in Her Majesty's Sensible System of weights and measures.

I would not pulling apart the valve train to chase one thou as measuring with feelers does have a certain amount of error, probably in the region of one thou. if it was two thou (0.05mm) thats a different story, I would shim it out

what was the temperature when measured? was the engine still warm or stone cold?

I would leave it for a few thousand kilometers and recheck, chances are it will close up
I'd be with you on that Bonza, I think a lot of people get afflicted by what we call 'micronitis' (now that we've gone all metric), a thou under maybe I'd get a bit worried but over? No, I'm too lazy to do all that work when it won't constitute a problem anyhow. Mind you the guy's got the top end in bits now so he may as well.
Given that he is going to do it, I'd aim for bottom limit, I agree with Dr F that they are unlikely to reduce much or quickly at the current mileage, smaller gaps will be guieter and give a tiny (unmeasurable) performance increase.

Last edited by GDCobra; 11-02-2012 at 05:20 AM.
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