Ops head clearance

[Ben Ballard]

Was just reading a post, "nova head clearance" and it crossed my mind that maybe my motor is not set up right. How do I check the head clearance and what should it be? I bought this motor used and don't know much about it. It did come with some head shims but I have no idea how many should be in it. I ask this question because I am having troubles turning it over with my starter... I do think my starter just ain't got enough "ass" to it, but am wondering if too much compression might be part of the problem too. Any help would be greatly appreciated. The motor is a ops .80 with a red head.

 

[Steven Bryant]

What starter are you using and how many volts?

 

[Ben Ballard]

It's a hobbyco starter 12 volt. It says it is good for a .90 engine but I have my doubts. I am powering it with a 12 volt motorcycle battery.

 

[Steven Bryant]

I use a sulivan dynatron on 12volts 110amp battery to start my 67's and it struggle, i have found that the cheaper starter do struggle to turn over anythink over a 45 so you might need to upgrade to a starter with more torque. I'm sure there are a few guys on here who culd help you or you could try http://www.gotnitroonline.com, i beleive these guys are the importers. Regarding your head clearance i couldn't comment as i dont run 80's.

 

[Ben Ballard]

Thanks Steven. Think I have a line on a better starter from another member. I am still curious on the head shim deal if anyone knows. I'm seeing that there is a lot for me to learn about nitro boats and the fact that my motor came with "extra" head shims is bugging me. I have looked on got nitro for info and alli have found is a exploded view and parts list. No info on how many or what thickness to use although they are only listing one part number for shims but no measurement on how thick they are.

 

[RodneyPierce]

Hey Ben, to find your head clearance you need to measure the distance from the top of the sleeve, to the top of the piston at TDC (top dead center). You also need to measure the distance from the "shoulder" of the head button (where it sets on top of the sleeve) to the squish band (portion that protrudes down into the sleeve). The difference in these two numbers is the head clearance. You will need to use a quality tool for measuring, as we are talking about thousandths of an inch here.

 

[Ben Ballard]

Thanks, I do own mics and dial calipers/ indicators. Just wasen't sure how these things were measured and what clearance I should be looking for.

 

[RodneyPierce]

I cant help you with the head clearance.

 

[Ben Ballard]

Rodney,Thanks For informing me how to measure it anyhow, it gets me a step in the right direction Any info is helpful.

 

[FloridaScaleBoater]

Thanks, I do own mics and dial calipers/ indicators. Just wasen't sure how these things were measured and what clearance I should be looking for.

Ben, Rodneys description "to find your head clearance you need to measure the distance from the top of the sleeve, to the top of the piston at TDC (top dead center). You also need to measure the distance from the "shoulder" of the head button (where it sets on top of the sleeve) to the squish band (portion that protrudes down into the sleeve). The difference in these two numbers is the head clearance." Is right on, the only thing I'll add, is to take the measurements at the 12-3-6-9 oclock positions around the top of the sleeve and head button,,,, average your 4 measurments you get.

on an OPS set head clearance at .016 to .018" also, where the squash (flat area) meets the bowl of the head button, take an exacto blade and take that sharp edge off.

Also, that starter will work just fine on 24volts and will spin anything you need to start with ease.. I start my gas Zenoahs with that starter on 24V

 

[Ben Ballard]

Thanks a bunch, will check my head when I get back to the shop.

 

[brad nichols]

You can also use plastic gage or even thin solder as a cheap and quick way of doing it. solder on top of the piston and turn engine over by hand and measure the squished thickness with a pair of callipers and that would be the clearance, then add shims if needed. this is just a quick way of doing it and not as tech. as others. plastic gage is the same way except it has a measuring gage on the package and comes in different thicknesses. Don't overly force the motor over, if stops hard you are using to thick a size. Brad

 

[tnrcboatracer]

Depending on the button volume and nitro % of the fuel, you can run less clearance. The lower the clearance the higher the MSV. I personally run about 0.010~0.012" on the 67 and 80 motors. But if it is a small volume bowl, it will not handle anything over 25~30% nitro. I have many different volume head buttons for the OPS motors. I use the Speedmaster gage which is a dial indicator through the plug hole. But you need to be careful if the motor has a dished piston crown. When measuring at 3,6,9,and 12 o'clock, the measurements should not vary more than 0.001, else you have an out of square head button.