CMB Torque Specs

[LeeWininger]

When assembling CMB's what do you torque your head bolts down to?

 

[Andy Nightingale]

I was having this conversation with some mates just yesterday and am wondering the same thing. Would love to hear a definitive answer of a torque spec

 

[ALLAN YUEN]

Show pic of torque spec sheet

 

[Wasted wages]

Answer is, there is no correct answer...

I'm sure the factory had a number when the motor was new, but so much depends on what bolts you are using, stainless,, OEM,, etc...

Plus how clean the threads are, type of lubricant or oil or sealant used...how many times the bolts have been cycled...all play into it.
You could get 50 different answers to the same question.

For most of us it's tightening by feel, using the same lube every time, tightening in a cross pattern, and then rechecking the bolts once the motor has been run a few laps and has gotten up to temp. I rarely use locktite, and if I do, it's the blue and only on endplate bolts, and carb drawbars.
Everything else is lubed with ARP thread assembly lube.... especially head bolts.

BTW...
ARP has a very nice catalog along with history of bolt manufacturing and the greatest minds in the fastener business... it free, and worth reading from front to back. You can learn a great deal about fastener technology from it.

To get one, I just went to their website and requested the catalog on the "contact us" page, and left my address... they sent me the catalog as well as a few stickers and other company info...

 

[Buckshot]

Use what Alan posted for values. Key is to be consistent and use a criss-cross pattern.

 

[Timbo Whalen]

Show pic of torque spec sheet

Thanks, Allan.

 

[BrianNeumann]

I began taking apart/assembling my .12 nitro engines when I started racing 6-7 years ago. Worried that I might damage something, i bought a screwdriver style torque wrench w/interchangeable bits. I found the proper general torque specs by doing a quick internet search based on fastener size, type/strength, & what it’s threading into. The torque specs I found match the chart that Allan shared in his post. Always used undamaged or new fasteners & o-rings. And tightened backplates or head buttons in proper sequence/criss-crossing like BuckShot suggested. So far I have not had 1 fastener come loose, break, stripped any threads, or developed an air leak. I would think that your engine will be assembled as close to factory specs as possible following all the advice given. Agree with Wasted Wages about the variables involved in a getting the true torque spec, so I inspect the parts, take my time & keep everything clean/lightly oiled.

 

[James Schmidt]

The rule is to not over tighten. Tighten in cross pattern. Keep even tourqe on screws. Use blue lock tight on back plate and carb.

Not worth getting in the weeds over for sure.

Thanks Jim

 

[Wasted wages]

I also think it's a good idea to back off head bolts if your going to store engines for any length of time. spray them down with your favorite penetrating oil or anti seize and screw in a turn or two. Head bolts are the most susceptible to freezing up and snapping off...

 

[David Ashcroft]

WWages strip complete in my opinion let the parts rot in good lube