head check

[Lay26]

the other evening i was working on my engines. I hit a wall on checking the head clearance. whats the best way to go i'm in the h34r: h34r: h34r:

 

[Propjockey]

Try this...bend a piece of soft solder in an "L" shape, insert through plug hole and turn the engine over, letting the piston squash the solder against the head. Carefully remove the solder and put a micrometer on the squashed part.

 

[Ron Olson]

There are some head guages made for this. I have one made by Dynamite that screws right in to the glow plug hole. You can do it several ways with this tool. Measure the TDC, remove the head and put it on something flat like a piece of glass and the difference between the 2 measurements is your head space. A cheaper way is to put a piece of solder in the glow plug hole then crank the motor over once. Remove the solder and measure the thickness with some calipers.

 

[Bart Drieghe]

Ron Olsen's way is to my opinion more precise ( the caliper way ) , if u are doing it with solder then u can have a fraction of difference because of the bearing .

Regards , Bart

PS yes i know , the caliper way takes the most time , when im short in time i'm doing it with the solder .

 

[boaterbill]

Terry Keely sells a head guage.

they come in a small key ring, they are L shape you keep trying different one untill you find the right one. Gary Preusse sells them also 630-279-2451.

Believe it or not the lead wire way is not very accurate.

Gary also sells a dial gauge (made by mhc) for measuring head clearance, you screw it on where the plug goes in. First you need to take the head button off the engine, set it on a piece of glass, screw the guage in the plug hole, turn the guage untill it hits the glass, use the pointer on the guage, turn the guage to the 0 reading, put the head back on and repeat the same proceure as above, you can then read the head clearance on the guage.

 

[izitbrokeyet?]

Sounds easy enough.but.........

What do you do when your piston has a Dish in it?

all of my 21's are this way and I have to measure the distance difference between the top of the sleeve and the piston rim at TDC then measure the projection of the head button taking into account the width of shims.

I suppose the solder method will work here too...but does anyone have a better way?

 

[Mike T.]

In gas engines I've found the solder method indicates about .004" more clearance than using a dial gauge. I believe it's because the piston tilts in the bore when solder is inserted on one side. Given that the piston has about .004" of clearance in the bore, that seems to be about what one would expect.

Also consider that the squish clearance might not be uniform all the way around in some of these engines (particularly gas). The push-up method below will measure the closest point.

To use a dial gauge to check an engine with a dished piston or non-removable head, check at TDC with the engine assembled, then remove the big end of the rod from the crank (or in a gas engine, remove the piston from the rod) and check while pushing the piston up till it stops.

 

[Don Ferrette]

"Gary also sells a dial gauge (made by mhc) for measuring head clearance, you screw it on where the plug goes in. First you need to take the head button off the engine, set it on a piece of glass, screw the guage in the plug hole, turn the guage untill it hits the glass, use the pointer on the guage, turn the guage to the 0 reading, put the head back on and repeat the same proceure as above, you can then read the head clearance on the guage."

Every engine I currently have has a dished piston so I use the Keeley guage set. The solder method sounds interesting, I'm going to try it & compare to the guage set.

 

[Mike Hughes]

You know when you at the lake and the boat ain't running right. Maybe you pulled the motor apart the night before, and you think to yourself "Did I get that head shim back in there?". The solder is a down and dirty method. It gets you the info you need with out all the trouble. If I have the time I use the mic. If not I make do with the solder.

Mike

PS Not to mention if the piston top is rounded, it is the only way.

 

[Propjockey]

Believe it or not the lead wire way is not very accurate.

How so, Bill? Anyone ever hear of "Plasti-gage"?

 

[Guest]

Don,

measure the depth of the dish, deduct that figure from the dial gage.

Plati-gage works, but all I found here is .002-.006, Fine if you want to drop to .006.But if you can find the right size plati-gage yes it will work.

Bill Heacock

 

[boaterbill]

Forgot to log in.

Measure the depth of the dish, with your caliper, then deduct that figure from the reading on the dial gauge. My caliper has a bar scale to measure depth also. Can't edit the post above, forgot to log in. Anyway this is what I meant to say.

Mike, I agree it is a down and dirty way of doing it, in a pinch it will get you close enough. I still don't like it.

After .006 in the plasti-gage all I could find was .010, so if you're going in between?

Bill Heacock

 

[DaveMarles]

I generally use the solder method because its quick and accurate. The dial gauge method and others are OK too but time consuming and I find mistakes can happen easier. The thing to remember is that the clearance measurement may be different between the solder method and other methods. Thats OK but you must remember not to compare your reading with a dial gauge to some else using solder. If I quote a clearance to someone I always say 'measured with solder' so that there is no confusion.

I guess if you ask 10 people you will get 10 answers on this one.

Dave

 

[boaterbill]

Thats a good point, to remember to tell how you do your reading.

But I disagree with you on the lead being accurate. In my experience it is close to .0004 off. Mainly due to cocking the piston when you use the lead method.

Yes the guage is time consuming, but them when I go hit the pond all that is taken care of at home, I don't change headclearances in the middle of a race.

Dopn, The Keely guages only go down to .010. At least mine doen't go below .010.

Bill Heracock

 

[Terry Keeley]

Dopn, The Keely guages only go down to .010. At least mine doen't go below .010.

Bill Heracock

We're getting ready to make another batch and will try to have them go down to 0.006" or so. After you find what your head clearance is you can remove shims (which are normally 0.1 & 0.2mm or 0.004 & 0.008") to get down below 10 thou...

 

[Guest]

Thanks Terry,

I'll ask Gary to send me a set when he gets them.

Bill Heacock

 

[DaveMarles]

Bill, I don't see .0004" being an issue. ot 5 people to strip down the same head assembly and measure it then I'd bet you wouldnt get more than 2 with the same measurement and if most were within .001" I'd be surprised. Probably the same might apply to the solder system but I can get consistent results with solder and thats what matters to me. Terrys system can also be affected by piston rock and so can a dial gauge or caliper measurement on modern engines with dished pistons. I have a set of Terry's gauges and a Speedmaster dial gauge gadget in the toolbox but they are just there to look flashy.

I think its one of those things that makes precision engineers wince but if it works then thats good enough for me. Anyway, after a few runs on the edge of detonation, the squish clearance isnt the same all the way around the piston because of erosion. Not that it has ever happened to me.

 

[gene gager]

been using the solder method for many years. buy ultra soft solder , .020 thickness from a welding supply shop. make sure you compress it in alignment with the piston wrist pin (to advoid piston rock). LOG YOUR RESULTS!! after the motor breaks in it will remain the same. when the motor gets tired you will find the readings get bigger and bigger rapidly. replace bearings and all other worn parts and start over again. geno

 

[Don Ferrette]

We're getting ready to make another batch and will try to have them go down to 0.006" or so.  After you find what your head clearance is you can remove shims (which are normally 0.1 & 0.2mm or 0.004 & 0.008") to get down below 10 thou...

Terry-

Tried to send you a P/M but it bounces back as not good e-mail address.

 

[Lake S.P.O.R.T.]

The solder method gets you pretty close if you are very careful about it. Still, if my dial indicator is handy i will take the time to use it. This leads me to another question. I run outboards mainly and they have angled squish heads. If the manufacturer goes to the trouble to put the angle there then why do some people remove it? Is this the same as saying, well why do they use a full pistion skirt when there are advantages to cutting it? Any help on that would be appreciated.

Mark