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Valve clearance

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Hi guys,

 

I have not yet needed to change any shims on my 1996 VFR 750. I have checked them a couple of times and changes are so small that it could be my skills being inadequate with the micrometer and feeler gauge.

 

Recently I read it is better they are off target value to the "smaller side" - I don't understand this argument... maybe somebody can explain this?

But it got me thinking, is it better to "hunt" being as close as possible to the target value. With my latest measures I realised that I can get them all better than 0.01 mm with just 3 new shims and moving some others around.

What do you do - leave the shims as long as clearance is within spec or do you go for the closest to taget value every time371993578_Skrmbillede2019-09-15kl_15_25_47.png.ad73970845762a8e0c777bbcce5bff4b.png?

 

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The reason tighter is considered better is because you get more valve lift, thus in theory more power, but 0.1mm will not show on a dyno. The second reason is no cam banging across the excessive gap. 

 

Best to adjust using move around & get as close to centre of range with what you have & minimum number of new shims. But each to their own. 

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2 hours ago, Mohawk said:

The reason tighter is considered better is because you get more valve lift, thus in theory more power, but 0.1mm will not show on a dyno. The second reason is no cam banging across the excessive gap. 

 

Best to adjust using move around & get as close to centre of range with what you have & minimum number of new shims. But each to their own. 

Right, thanks, Mohawk - I assume you mean 0.01 mm 🙂 which would less show up on any dyne run.

 

In theory the taget gap is precisely removed by expansion. A smaller value - applying your theory - would lift a tiny bit more but also not close valve, which I think is worse. I would think a "very small larger value" (so a very small gap at normal operating temperature) would be "filled" by the oil film (and therefore still no banging)

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Err no I meant 0.1mm as in one tenth of a mm extra lift would not cause a noticeable difference on a dyno. Anything in the 100th of a mm would not be noticeable anywhere.

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Well - adding 0.1 mm would bring you way out of spec (the range is just 0.03 mm) 😯 So even going for the max extra lift at 0.03 mm would mean no additional power as per your comment.

 

So, I guess it is fair to say that their is no argument for using a tight gap?

 

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Well there is one argument for it, but only post initial check. So if a valve clearance is tightening during run, then a slightly loose setting helps keep it in spec longer. On the flip side if a clearance is loosening, then a slightly tight setting keeps that in spec longer too.

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On 9/18/2019 at 12:10 AM, Mohawk said:

Well there is one argument for it, but only post initial check. So if a valve clearance is tightening during run, then a slightly loose setting helps keep it in spec longer. On the flip side if a clearance is loosening, then a slightly tight setting keeps that in spec longer too.

My thinking is based on no gap at operating temperature when gap with cold engine is "in the middle" of gap range. This thinking might be wrong.

 

It does not make sense a valve should not close completely (backfire or missfire) and therefore a zero gap is achieved with a hot engine at the lower end of the gap range. So any larger gap than the smallest allowed gap on the cold engine would introduce a gap on the hot engine.

 

Choosing to set gap to the smallest allowed would not leave room for seat wear and could be the reason why the "taget gap" is a little larger than the smallest allowed gap.

 

With this line of thinking your argument would also hold true - any larger than min gap would reduce power slightly.

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as far as  i know clearance should be checked and set on a cold engine.

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9 minutes ago, squirrelman said:

as far as  i know clearance should be checked and set on a cold engine.

Yes - if my post suggest otherwise then it's a mistake. I have added "cold engine" in one place to clarify.

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As I passsed 35k miles recently, probably time for me to check the valve clearance; was wondering if there is a video I could watch to get me ready for this?

Also what gaskets need replaced?  This will be a Winter project...just getting started gathering parts...well...except shims of course...have to wait to see what I need.

 

Thanks

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The Honda shop manual is very good and you can download it from this site (look for "download" on the left-menu while on the frontpage).

 

Most likely the gaskets can be reused. Make sure to clean surfaces. The surface can be a little rough on the exhaust side of the front cylinders as they take a lot of dirt and water (1000 grit sandpaper can sometimes do the trick though be mindful about not getting anything into the engine).

The manual refers to Hondabond A which I have never found anywhere - rather use nothing at all than liquid gasket.

 

Most important: be very mindful not to drop anything into where the sprockets sits - cover with a piece of cloth.

 

If some clearances are off, then I suggest you measure all shims while you are at it. That means taking the cams out. Before you begin take pictures of how things look - including the timing marks. When removing the buckets the shim may stick to them (or not) - be very careful they dont drop into the engine!

I suggest you do one set of cylinders at a time so you only have to worry about one set of timing marks at any one time.

The front cams sits among frame and radiator making space to work on somewhat limited. Begin with the rear - those cams easy to get to.

Be careful to check the timing marks AFTER you have bolts all the way in (before/after being torqued) - the sprocket moves about 1/2 a tooth during tightening bolts. 

 

You need a micrometer and a set of fine feeler gauges. For the cams you need a torque wrench.

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The only parts that you may need are the rubber-backed washers under the camcover bolts. These are the only thing that is applying any squish force to the camcover gaskets, and over time they get squashed themselves and may not be able to provide enough clamping force when re-fitted to ensure a good gasket seal. I've had experience of this on my 1990 ST1100 which sealed fine until after a valve check. A new cam cover gasket didn't fix that, but new rubber-washers did. You can not (and must not) just apply more torque to the bolts as these are designed to bottom-out with relatively little torque; too much torque causes them to either snap off or break the thread in the head...

 

You may also need a little gasket sealer just around the half-moon sections of the gasket, I only ever use a thin smear in this area. 

 

For the valve check you need to make sure the cam lobe is pointing away from any valve you measure. I personally find imperial feeler gauges easier to work with as the clearance spec is easier to assess. E.g. intakes should be 0.006+/-0.001 inches. So if I can fit the 0.006 feeler but not the 0.007, then the spec is in the middle. And if I can fit the 0.007 but not the 0.008, at the upper edge. If 0.005 fits but not 0.006, at the lower edge of the spec. As long as the cleanace is within the specified range I leave well enough alone. If a 0.008 fits, then it is time for a shim change, likewise if I can't even get 0.005 to fit. Of course there is a little bit of imperial to metric conversion needed when figuring out which new shims are needed but you'll be doing some maths anyway.

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Ok...cam cover rubber-backed washers....., what about the right side case cover gasket....I assume it will need replacing?

 

I do not have a micrometer, only calipers....guess I will need to find a micrometer somewhere.  Torque wrenches I have.

 

Any chance if the rear is ok, then the front is ok?....

 

Thanks

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Right side case cover??? You only need to unscrew the access cap, that has an o-ring under it that should be infinitely reusable. Grease it before reassembly and don't over-tighten.

 

I use a cheap digital vernier caliper to measure shims but a micrometer should be cheap as well, <$20? He who dies with the most tools wins, you know! You may get lucky and be able to read the printed size on the shim that you pull out to replace but then again...

 

Regarding the front and rear shims being the same...who's to say a previous owner also made this assumption, or only worked on the back head? If it was my bike I'd want to at least check the clearances. 

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Look up the bucket & shim record method. Basically check every valves clearance. Record it against each valves location on a table. Then if you have to remove the cams to change one, you can compare shims from a tight ish valve & a loose one. Often you can switch them around to get a middle of the road clearance. So no mew shims needed, or less of them at least. 

 

Get yourself a magnetic picker tool to lift the buckets. Often that will lift the shim too ! 

 

And remember the cam anti lash gear painting BEFORE. you lift a cam. It really does make refitting much simpler.

 

Have fun.

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Regarding the right side crankcase cover removal, and this would be should the cams need removal....I misread the manual, thought it referred to marks on the "clutch", it was "starter clutch"....my bad.

And yeah I will check all valves....my question regarding if the rear valves are okay, then probably the fronts are as well, I was just wondering if that would normally be the findings; same as the inverse, if I find out of spec clearances on the rear valves, then I will most likely find them on the front set as well.

 

Got the hint of painting the cam anti-lash gear BEFORE removing anything.

 

Looking forward to doing this in Nov/Dec/Jan....when it becomes just too cold to ride.

 

THANKS!

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On mine #3 always gets tight, its the HOT cylinder IMO with the rear headers out back & the thermostat & rad hose restricting air around it. 

 

So its my gauge for the rest. IME The inlets tend to tighten up & the exhausts tend to loosen up. 

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41 minutes ago, Lannyl81 said:

And yeah I will check all valves....my question regarding if the rear valves are okay, then probably the fronts are as well, I was just wondering if that would normally be the findings; same as the inverse, if I find out of spec clearances on the rear valves, then I will most likely find them on the front set as well.

 

I would not assume that - when you are at it, check and measure them all. That makes you sleep better at night 🙂

 

After having done the rear cylinders, I'm sure you will conclude it really is not that scary. Although access to the front cams are worse, it not as you start to through tools in anger.

 

You will need a micrometer as you need the 0.01 mm resolution. Also make sure your feeler gauge is fine stepped (so you can produce increments of 0.01 mm within the allowed range) - those cheap ones for spark plugs won't do the job

 

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My feeler gauges have the fine steps, just need to get the micrometer yet.

 

Thanks again for the information.

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Well I finally started, got the rear cover off and took measurements.  Found that #1 intakes were both good at 0.006; outside exhaust was tight at about 0.008, inside exhaust good at 0.010.

On #3 the inside intake was good at 0.006, but outside intake was tight at about 0.005.  The exhaust followed the intake; inside good at 0.010, outside tight at about 0.008.

 

Have not pulled the front cover off yet, need to remove more plastic first and probably just go ahead an pull the radiator off as I suspect I will be removing all cams.

 

I noted a small dab of silicon on the gasket at the "wheels", was this done at the factory or was this a previous owner?

 

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If you are referring to sealand applied to the "half moon" section of the cam cover gasket, that is manufacturer recommended whenever refitting these gaskets. I tried going without this and ended up with a fine oil weep. 

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Terry; yep that is exactly what I am asking about.  Hopefully I can get the old sealant off so I can put a small dab of new on there.

 

Anyways got the front cover off, very similar results......#2 intakes were both tight at 0.005, exhausts were both at 0.010.  On #4 inside intake was a loose 0.006, outside was tight at 0.005, inside exhaust was at 0.010, but outside exhaust was tight at 0.008+..

 

 

So now I have to decide if I should remove the cams and take care of all the tight ones or leave all alone............??????

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You have valves out of spec and now you know... their is no going back now 🙂

 

You don't need to remove the radiator - remove the bolt on the left-hand side securing the bracket on the engine and swing radiator forward. Secure radiator in forward position with rope.

 

The Honda service manual is very clear with good pictures. Take your time with the timing marks and rotate the crank a couple of times to get the hang of it.

 

Remember, their is a first for everything... 🙂

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Valves are not really out of spec....just at the tight limit.....but agree with you.....remove the cams and change the shims to get the clearance in the middle of the spec.

Have been reading the Honda Service Manual, looking at the pictures as well.....just a bit nervous.

 

I did remove the radiator....it is easy and quick to do...yields more room....plus I can clean-out all the bugs (again).

 

Time to head-out to the garage.....

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Took one cam out at a time, removed the shims that needed to be, measured them, determined size of new ones needed, ordered them.  I put the cams back in for safe keeping while I am waiting for shims to arrive next week.

 

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