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  #1  
Old 25-11-2009, 14:52
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VFR 1200: Valve Adjustment

I'm looking in the new BIKE mag and there is a picture of the top of the engine and I'm sure I can see valve adjusters like the ones you would get on a FORD Fiesta or any other push rod set up. The rockers have wheels at the end of them that run up against the camshaft. Am I seeing things?

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Old 25-11-2009, 15:02
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You might well be seeing things - we'll never know.....

However, ISTR that the VFR1200 heads use the single cam design which Honda used in the CRF cylinder heads and yes there is a threaded adjuster and locknut for the tappet on the exhaust valves; although why there's only one in this pic of a CRF head escapes me. The intake valves use the more common shim under bucket arrangement.

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Old 25-11-2009, 15:07
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The picture that I am looking at has a screw adjuster for each valve. Does this mean that adjusting the valve clearances is going to be a doddle?

I have not read all the words yet. It was the picture that caught my eye.
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Old 25-11-2009, 16:10
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Quote:
Originally Posted by mathsman View Post
Does this mean that adjusting the valve clearances is going to be a doddle?
Yes for the exhausts but ISTR that the inlets are the same as in that pic of a CRF head which I posted in that the inlets have shims under buckets.

You've obviously got your new copy of BiKE before mine has been delivered. I don't have access to the pic.
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Old 25-11-2009, 16:13
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That CRF head appears to have a cam drive gear - what's the 1200 going to use? And I assume (given that the Honda web site hasn't made a big thing of it) that it will not have variable valve opening and timing. Retrograde step, that...
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Old 25-11-2009, 16:30
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Camchains - pics at the bottom of http://www.bikersoracle.com/vfr/foru...d.php?t=104425

Strange though, I can't see any tensioners!
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Old 25-11-2009, 16:57
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Strange though, I can't see any tensioners!
That's going to remove some people's biggest complaint about CCT reliability then
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Old 25-11-2009, 17:04
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Quote:
Originally Posted by nealeb View Post
That CRF head appears to have a cam drive gear
No, that's the cam chain sprocket.
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And I assume (given that the Honda web site hasn't made a big thing of it) that it will not have variable valve opening and timing. Retrograde step, that...
Retrograde....? That's ironic given the amount of criticism that's been levelled at the VTec over the years.

I believe that the first iteration of the 1200 doesn't have any kind of variable induction or exhaust but that forthcoming variants will do more than that and shut down a couple of cylinders when they're not required.
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Old 25-11-2009, 17:21
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Quote:
Originally Posted by Schtum View Post
You might well be seeing things - we'll never know.....

However, ISTR that the VFR1200 heads use the single cam design which Honda used in the CRF cylinder heads and yes there is a threaded adjuster and locknut for the tappet on the exhaust valves; although why there's only one in this pic of a CRF head escapes me. The intake valves use the more common shim under bucket arrangement.

It looks like the exhaust cam follower is bifurcated around the spark plug tunnel and operated by the central cam lobe. The follower with the adjuster lock nut seems to be operated by a cam on the end of the shaft, through a trunnion. VTEC? The 4 minute mark here http://www.youtube.com/watch?v=bfdvmEpP5gA might make it clearer.

Last edited by Egg on Leggs; 25-11-2009 at 17:29.
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Old 25-11-2009, 17:40
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Quote:
Originally Posted by Schtum View Post
Retrograde....? That's ironic given the amount of criticism that's been levelled at the VTec over the years.
Is that the first time that deliberate irony has ever been spotted on this forum?

Quote:
Originally Posted by Schtum View Post
No, that's the cam chain sprocket.
I tried looking at a zoomed image but couldn't quite decide if it was a sprocket or a spur gear. However, it did lead me to look more closely at the bifurcated rocker and what it did. Look very carefully at the adjuster. It does not appear to bear on the valve stem at all, but does it bear on the non-valve stem fork of the other rocker? Theory - the bifurcated rocker is always operational but the "adjuster" rocker is VTEC-operated. When it does operate, it opens its own valve and modifies the opening time/lift of the "normal" valve as well via the adjuster bearing on the forked rocker.
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Old 26-11-2009, 00:07
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My reading of the CRF head is that the adjuster screw is on an arm whose pivot is not in line with the pivot of the forked valve opener. Hence the end of the adjuster screw would slide along the valve opener as it moved up and down.
This does not seem to be a good idea at 10,000 rpm.
So what could it do at low rpm?
Howzabout an exhaust valve opener - the thing they fit to big singles to make them easier to start. What size is that CRF engine - 450cc? - sounds big enough to need an opener to me.
Note the cam that the inboard end of the extra arm runs on is outboard of the bearings for the camshaft, and there's some weird gubbins on its end. This seems to suggest that it is not part of the regular valve operating system

As for the VFR1200 CCT I see summat at the rear of each camchain in the Bike pic that extends the full length of the chain tunnel from a bit sticking up behind the camshaft sprocket and down to what could be a spring near the primary gear, plus a bolthead or two on the back edge of the casing to hold each in place.

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Old 26-11-2009, 08:17
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This all reminds me of that Monty Python cartoon where they recreated a dinosaur from a giant fossilised thumb! It would all be so easy to understand if you actually had the object in front of you...

I had been influenced by trying to find a use for the left-most cam but of course it is timed the same as the cam at the other end of the shaft and operates the inlet valve whose spring you can just see - so one cam and a forked rocker operates the two exhaust valves and each inlet valve has its own cam and direct operation via a shim-and-bucket. Exhaust valve lifter seems like a good option, then!

How do you reckon that the exhaust valve clearance is adjusted, then? Eccentric rocker shaft? I can't see a pinch bolt to lock it if so, but it could be turned via the exposed end that you can just see.
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Old 26-11-2009, 16:57
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The exhaust valve clearance is adjusted by shims that fit directly on top of the valve stem. See here-

http://crfsonly.com/howto/crf250x/cr...adjustment.php

Ian..
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  #14  
Old 27-11-2009, 12:14
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I'm not familiar with the CRF, does that model use a kickstart ? 'Cos that adjuster looks more like a valve decompressor to me ...


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