How to use plastigauge for measuring head clearance

[Terry Keeley]

I've been using 0.016" solder for years with a mic to measure it, it repeats every time, just bend a bit and stick it in the glow plug hole.

It takes all the slack out of the rod/wrist pin/crank just as it is while the engine is running, I run 0.012" for everything up to my 90's which I run at 0.014".

https://www.amazon.ca/AmaoeTin-Electrical-Soldering-Content-Melting/dp/B09WYQ8W9W

Flame away.

 

[XtremeRcBoats]

I've been using 0.016" solder for years with a mic to measure it, it repeats every time, just bend a bit and stick it in the glow plug hole.

It takes all the slack out of the rod/wrist pin/crank just as it is while the engine is running, I run 0.012" for everything up to my 90's which I run at 0.014".

https://www.amazon.ca/AmaoeTin-Electrical-Soldering-Content-Melting/dp/B09WYQ8W9W

Flame away.

Thanks Terry, this is for the K&B67 project. Tried you head button today and first need shims. I found a 0,3mm shim in another K&B67 but before TDC the piston hits the button, so i first need to find some shims. Does anyone perhaps know if shims for other size engines can be used for this one?

Hi Daniel,

I have not seen a squish gauge in use or even photos of how they actually measure. But how do they account for dished/domed pistons and tapered head button squish?

I have just been using a digital vernier and also a digital depth gauge to get my numbers...it does not really account for dish and tapers...but in all honesty, it is how I have seen some REALLY FAST guys do it, so it must be ok

Hi Kris, can you tell me how this work?

How hard can it be!

Hi Timothy, Can you tell me how to do that with this tool?

 

[timothy johnson]

Thanks Terry, this is for the K&B67 project. Tried you head button today and first need shims. I found a 0,3mm shim in another K&B67 but before TDC the piston hits the button, so i first need to find some shims. Does anyone perhaps know if shims for other size engines can be used for this one?


Hi Kris, can you tell me how this work?


Hi Timothy, Can you tell me how to do that with this tool?

Daniel's racing in the vendor section sells the adapter and explains its use. Rossi sales, Speedmaster, also sells an adapter.
In short you first install the adapter in your removed head button and zero it out on a flat surface. You then install your head button on your engine and move the piston to TDC and then read the difference from zero to the top of the piston.

 

[Terry Keeley]

MECOA lists the bore as 0.962" (24.4mm), the CMB 67 is 24.6 so those shims would probably work.

https://www.mecoa.com/kb/marine/marine_inboard.htm

 

[Tom Foley]

I knew guys that ran zero head clearance..

and relied only on the oil in the fuel to keep the piston from touching the head button and the slack in the crank/rod bushing was the only
Clearance.. the piston never struck the head.
Just a perfect burn pattern on the piston crown.

They used head volume to make changes in the combustion chamber.. mangled a lot of plugs, but once they figured out the right volume on the head button no shims were used to set squish..

My VAC .91 engines run like this with a measured .007" head clearance . The pistons show evidence of barely touching the head button .....barely ! If they were actually touching it would be catastrophic. They really scream at this setup !

 

[Wasted wages]

My VAC .91 engines run like this with a measured .007" head clearance . The pistons show evidence of barely touching the head button .....barely ! If they were actually touching it would be catastrophic. They really scream at this setup !

It works !
I’ve witnessed it in action.. it means there is basically less than .001-.002 clearance in the total piston/rod/crank pin stack and oil has to be the limiting factor from keeping the piston from striking the head..
run it rich and send it!!!

 

[Kent Fowler]

Quick question, doesn't expansion and contraction from heat cycles change the head clearance, would you get a better reading / more accurate on a hot engine with head clearance then cold?

 

[Alan Elzer]

I've been using 0.016" solder for years with a mic to measure it, it repeats every time, just bend a bit and stick it in the glow plug hole.

It takes all the slack out of the rod/wrist pin/crank just as it is while the engine is running, I run 0.012" for everything up to my 90's which I run at 0.014".

https://www.amazon.ca/AmaoeTin-Electrical-Soldering-Content-Melting/dp/B09WYQ8W9W

Flame away.

Agreed, same here for 30 yrs

 

[Brian Schymik]

I use Terry Keeley head gauges! Wonder why Terry Keeley doesn’t?