How do you measure head clearance?

[Kez]

I measure mine using a caliper with the depth gauge through the glow plug hole when the engine is at TDC. Then I measure it again with the head on a machinst block. I know this approach is not ideal because it does not take the slop in the conrod, wrist pin and crank into consideration. If I have a lot of clearance in the conrod, I may run a risk of the piston hitting the deck.

I also read about using a piece of solder and stick it into the glow pluh hole with a L bend. After turning the piston through TDC to remove it and measure the flattened solder with a micrometer. I have never tried it as I do not like the idea of compressing the solder in the engine. And this method still preload the slop so that I do not know whether the piston will be hitting the deck at tight clearance.

I do not need to squeeze the last couple of RPM from my engines so I leave the head clearance on the high side. If I know how to measure it correctly, I would like to set it tighter.

So what is the proper way to measure head clearance?

Thanks,

kez

 

[moparbarn]

what you're doing now is as accurate as any method. the solder method is safe enough, if you use very thin/small diameter solder. an electrical supply store or jewelery supply would be good sources. just be sure to get a non flux core solder. plastigage works well also, use the same method as solder. since most head clearances are set at .006" and up, rod play shouldn't be a big issue. .004" is a HUGE amount of play in our engines, .002" would be max allowable before rod replacement, imho. as an auto tech, i've set adjustable valves as tight as .003", easy to feel the play at the rocker arm, it's more than you might think........

 

[camaroboy383]

i use two methods,,,,a dial caliper,,,with the head button off...measure top of sleeve to top of piston at tdc..if you can roll it through a couple times to make sure you have the correct measurement....the measure the button,,,from the sleeve land to the squish band,,,this can be tricky with angled squish bands,,,,just make sure the end of the caliper is square to the surface you are measuring... i use this method when modding engines to figure out what im cutting in the lathe... when the engine is done the head space is set using platigauge as robin stated....i never liked the solder method due to the stresses it puts on one side of the piston when spinning the engine through...

alden

 

[lohring]

Don't be afraid to run low head clearances. The big improvement in 3.5 engines is near zero running head clearance. That's the secret in OS 3.5 stock outboards. We have run Quickdraws at head clearances that give piston strike marks on the head button. Aprilia runs their race motorcycle engines similarly according to some knowledgeable sources. The caliper method can give an approximation of running clearance if you push up on the piston to take up clearances. I use a dial indicator in an adapter in the plug hole.

Lohring Miller

 

[Al Hobbs]

Fastest heat racing boat I ever saw was Andy Brown in Slovenia, 2006. He had no head clearance on a K90. Andy brought it in after the first heat and people were lined up to buy that boat and engine.

I guess the only clearance was the little bit of slop in the rod. But, it was not a stock head button either.

Al Hobbs

 

[misshydro]

I measure mine using a caliper with the depth gauge through the glow plug hole when the engine is at TDC. Then I measure it again with the head on a machinst block. I know this approach is not ideal because it does not take the slop in the conrod, wrist pin and crank into consideration. If I have a lot of clearance in the conrod, I may run a risk of the piston hitting the deck.

I also read about using a piece of solder and stick it into the glow pluh hole with a L bend. After turning the piston through TDC to remove it and measure the flattened solder with a micrometer. I have never tried it as I do not like the idea of compressing the solder in the engine. And this method still preload the slop so that I do not know whether the piston will be hitting the deck at tight clearance.

I do not need to squeeze the last couple of RPM from my engines so I leave the head clearance on the high side. If I know how to measure it correctly, I would like to set it tighter.

So what is the proper way to measure head clearance?

Thanks,

kez

could use plastic gage like you use on automotive cranks,to check on bearing clearances..

 

[moparbarn]

alden, you can get some very thin/fine wire solder through jewelry repair shops. not just silver solder, but some very soft alloys. too. very little stress on the internals B) .

 

[Ronald Matthews]

what you're doing now is as accurate as any method. the solder method is safe enough, if you use very thin/small diameter solder. an electrical supply store or jewelery supply would be good sources. just be sure to get a non flux core solder. plastigage works well also, use the same method as solder. since most head clearances are set at .006" and up, rod play shouldn't be a big issue. .004" is a HUGE amount of play in our engines, .002" would be max allowable before rod replacement, imho. as an auto tech, i've set adjustable valves as tight as .003", easy to feel the play at the rocker arm, it's more than you might think........

Unless i have forogten all motorcycle tuning tips on triumph bikes, on the intake rockers it was 1 thou just so you could feel it, on exhaust it was 3thou or just till you could hear the click.

 

[HTV Boats]

I prefer a dial indicator with an adapter for the glow plug hole. Zero the button on a machinist block or glass plate works for me. Then install the button and torque it down, roll the engine over TDC and get clearance. Rod clearance wont affect change while running as compression will keep the piston pinned to the rod. When I use solder and a caliper I never get consistant readings, maybe due to pistons rocking slightly compressing solder.

Mic

 

[mark voorhies]

I measure mine using a caliper with the depth gauge through the glow plug hole when the engine is at TDC. Then I measure it again with the head on a machinst block. I know this approach is not ideal because it does not take the slop in the conrod, wrist pin and crank into consideration. If I have a lot of clearance in the conrod, I may run a risk of the piston hitting the deck.

I also read about using a piece of solder and stick it into the glow pluh hole with a L bend. After turning the piston through TDC to remove it and measure the flattened solder with a micrometer. I have never tried it as I do not like the idea of compressing the solder in the engine. And this method still preload the slop so that I do not know whether the piston will be hitting the deck at tight clearance.

I do not need to squeeze the last couple of RPM from my engines so I leave the head clearance on the high side. If I know how to measure it correctly, I would like to set it tighter.

So what is the proper way to measure head clearance?

Thanks,

kez

I'm sure just measuring the head button and TDC gets you real close, but I take feeler gauges, take them apart, and use the individual gauges from

.001 to .014 lets say, cut them with tin snips to a width that will fit in glow plug hole, anneal and bend at end 90 degrees so it will go into plug hole

and hit I.D. of sleeve. Then turn engine over, when it bumps tight, with proper feeler gauge, you have a positive measurement, but still pre loads slop, I guess

that has to be considered, can't be more than a .001 or .002 ? I don't run clearances that close.

 

[Jack Brady]

With the solder method if you take off the head and lay a piece of solder all the way across the top of the piston and also in line with the piston rod you dont get piston rock. Both ends of the solder should have the same reading.

 

[Neil LaGarry]

I was told to use a piece of wax from a candle. Works for me.

 

[Daniel's Racing]

The most accurate way is to use a digital gauge in the button glow plug hole and hold the loose piston up against it(recording the number on the dial before resetting the gauge to zero and record it for future repeat squish gauge measurements on that engine)and reset the gauge to zero. Now without removing or turning off the gauge assemble the piston in engine and button on top and bring engine to TDC and the lowest number you can get the gauge to read would be your actual true squish reading.

If there is any dish or dome to the piston you will still be correct.

 

[RodneyPierce]

like above, i recommend a gauge.

 

[SeanKewley]

I take feeler gauges, take them apart, and use the individual gauges from

.001 to .014 lets say, cut them with tin snips to a width that will fit in glow plug hole, anneal and bend at end 90 degrees so it will go into plug hole

and hit I.D. of sleeve. Then turn engine over, when it bumps tight, with proper feeler gauge, you have a positive measurement, but still pre loads slop, I guess

that has to be considered, can't be more than a .001 or .002 ? I don't run clearances that close.

That's how I do it.

 

[LarryConrad]

On engines with flat top pistons and standard plugs I use a Speedmaster head clearance gauge. On the ones with turbo plug heads or dished pistons I use a digital depth micrometer.