Valve guides

[charles.bulloch]

Hi all, again,

Since my 1938 VH motor uses oil I would like to check the clearance of the valve guides. How do I do that?

Charlie

[dave.owen]

Valves should be a good sliding fit no rocking movement. Or measure internal size and valve stem against figures in waller

[cmfalco]

Valves should be a good sliding fit no rocking movement.

That's not quite the case. I have Gold Star valve guide specifications at hand, so I'll use them. The inlet calls for a clearance of 0.0010"–0.0013" and the exhaust 0.0015"–0.0020". The next photograph shows a valve guide I made, with the reading on the split ball gauge showing that the ID varies by less than 0.0001" along its entire length.

The next photograph shows a 0.3750" gage pin is a snug slip fit in this guide.

The final photograph shows schematically that a 0.3710" (i.e. a 0.004" clearance) gauge pin rocks back and forth by 0.0037", i.e. by almost the 0.004" clearance.

Not shown is a 0.374" gage pin (0.001" clearance, as for an inlet valve) is a loose slip fit, and a 0.373" gage pin (0.002" clearance, as for an exhaust valve) has a perceptible side-to-side rock.

[nevhunter]

An inlet guide will rarely seize so a free movement with no perceivable Play is OK . Exhaust fits are a different thing due a lot more temp involved in Aircooled and particually CAST iron Head Motors where .004" on a 3/8" dia stem is Normal. Chrome plated stem or nitrided with stainless is essential to resist "galling" and resultant rapid wear. An effective Aircleaner makes it all Last a bit Longer. Rockers make wear worse on OHV set ups so try to get the Valve length such as it makes a right angle with the Rocker Pivot centre at the 1/2 open Position. Short valve guides wear faster, but you usually can't do a lot abut that If you don't design the Motor. Have the Bore of the guide concentric with the OD Or you will have to cut the seat More Good finishes make initial guide wear much Less and the dia must be constant.

[charvey]

Hi All,
When I rebuilt my engine 20 years ago the inlet valve had very slight play and the exhaust a bit more and it seemed fine no tightness unlike the first ducati V4 which suffered valves seizing up and locked engines on the first 1000 engines sent out reported in the MCN they were sorted quickly.
Just a slight bit of side play on the inlet and a bit more on the exhaust as I said hope it goes well. Clive.

[charles.bulloch]

Hi, all, thanks for the replies.

On reading Waller there seems to be 0.002" clearance on the inlet valve and 0.004" on the exhaust. I might try and measure this with a dial guage. I'll experiment with a spare head.

[cmfalco]

To add to my previous post, since my gage pin set is in increments of 0.001", I measured the bore of the guide with my 3-point gage that reads to 0.0001". As the next photograph shows, the bore is precisely 0.3750"±0.0001".

I then measured the side-to-side clearance with a 0.3690" gage pin (0.006" clearance) and found it to be 0.0058". So, together with my previous measurements, the results are linear over the range of interest to us, and the movement directly gives the clearance.

These results mean that, absent access to precision internal measuring devices, a simple 0.001" dial indicator can be used to obtain a reasonably-accurate determination of the clearance from the side-to-side movement of the valve stem measured immediately above the top of the guide.

[simon.holyfield]

To add to my previous post, since my gage pin set is in increments of 0.001", I measured the bore of the guide with my 3-point gage that reads to 0.0001"...

For my education (and perhaps just a little indulgence in engineering OCD), would you show us what the 'business end' of that gauge looks like?

I'm guessing you are passing a taper in between a number of fingers which open in the bore, and the micrometer scale is effectively measuring the distance the taper moves? What range does it have?

[mark.prizeman]

I was curious too.
Look up 3 point bore gauge on eBay...

[cmfalco]

What range does it have?

The following photograph shows the working ends of the two types of gauges that cover the range around 0.375".

The split ball gauge on the left only makes contact at two points on a bore, while the three probes of the bore gauge on the right make contact along three lines that are ~0.1" long.

If a bore is perfectly cylindrical, both gauges will give the same result. However, if there is taper, or if the "cylinder" is lobed, they will give different results. For example, if a cross-section of a "cylinder" is a simple ellipse, rotating the split ball gauge by 90° will give both diameters, while the points of the bore gauge won't be able to do this. As this example shows, each gauge has its purposes. For some measurements, both are needed to provide the desired information, and for certain problematic situations (which, luckily, are seldom encountered in motorcycle-related work), neither can give perfectly accurate results.

As for range and operation, my split-ball set that covers the ⅜" of this valve guide has 7 balls that each nominally has a range of 0.020". The balls squeeze on the taper at the end of the needle that can be seen in the photograph, that in turn pushes upward on a dial indicator. Each time a different probe is attached, the instruments has to be calibrated using a ring gage or micrometer.

I don't know what the internals of the bore gauge look like, but they must be based on a taper as well. The one for ⅜" covers 0.350"–0.425", so a total range of 0.075". Each individual bore gauge maintains its calibration (although, I always check before making a critical measurement, to be sure).