Torque My super webco heads

[rd400greenhorn]

Hi guys

What do I torque these down to?
There are o ring seals in Them

[Dvsrd]

Hi guys

What do I torque these down to?
There are o ring seals in Them

I would use 20 Nm, same as most M8 fasteners, and factory spec on the 350. Torque is mostly depending on stud/ bolt size and grade. Not so much on seal or gasket type

[m in sc]

i set mine to 18 ft lbs  (which is 24nm). no issues.

stage the torque, i went 6, 12, 18. oiled threads. and, my head bolts are aluminum and they held up just fine, no worries. 

[rd400greenhorn]

Thanks guys
I went with 20nm

I Will see if thats enough eventually

[m in sc]

fyi:


found here:

https://www.engineeringtoolbox.com/metric-bolts-maximum-torque-d_2054.html

lots of good info on engineering toolbox.

keep in mind, that's maximum per fastener per grade.

[Dvsrd]

i set mine to 18 ft lbs  (which is 24nm). no issues.

stage the torque, i went 6, 12, 18. oiled threads. and, my head bolts are aluminum and they held up just fine, no worries. 

Mark,
What is your take on cylinder distortion caused by the cylinder/head studs? Since you use a higher torque (i.e stud tension) Did you have your cylinders honed with "stress plates" fitted, to simulate a torqued assembly? At least in the Harley world, that was common practice for a while.

[Dvsrd]

fyi:


found here:

https://www.engineeringtoolbox.com/metric-bolts-maximum-torque-d_2054.html

lots of good info on engineering toolbox.

keep in mind, that's maximum per fastener per grade.

Yes, Engineering Toolbox is a great resource for many things.
As I'm sure you are fully aware, fastener torque values is a tricky subject, depending on many factors. Like no washer, regular washer, or a hardened thick washer. Bolt material and surface treatment, i.e. ss, black steel, electrolytic zinc, hot dip zink. Etc.
And lubrication of threads and under bolt heads. Oil, grease, copper grease, even Loctite act as an assembly lubricant.
The target is to apply a certain stretch force/elastic elongation of the bolt. Newer cars and bikes often specify a fairly low torque value, followed by additional tightening of a specified angle. This method is better, but unfortunately no data is available for our old bikes.

[m in sc]

that's a lot of apples to oranges,  bit I see where you are going. however, you can calculate torque and angle to these. but it's not necesary. the stretch on the bolts is minimal, especially at 18 to 20 ft lbs across 4 studs. 
when I worked at atlas copco/desoutter/cp we used to give seminars on fastening. where most if the torque + angle applications were use was also with single use fasteners,  ge locomotive was a notable one (rod bearing cap applications). however,  that's not what we are dealing with withe these old dinosaur motors.
My reasoning and past experience with rd motors us that, when we hot rod them and get 20,30, 50 percent more power out of them, and you run stock torques, you run the risk of stretching the bolt under power developing a possible head gasket leak, and/ or the head shifting somewhat. 
early on, when I was still using stock style head gaskets I'd see leaks more frequently at the 15 ft lb settings. I figured that with a bit more torque things would hold together better, and going by what the fasteners could take, I increased the applied force, and have never had an issue since. j mean, you're NOT going to break a bolt.   theres no downside, and there's no need for a torque plate for boring in cyls like this to fend off any deflection of bolt tightening  . HD cyls bolt at the bottom and top separately.  aircooled rd motors sit under compression when installed , this amount of tightening wont deform them at all.
I've never had an issue ,, you're definately over thinking it on this I think.

[RSW46]

I would recommend caution when looking at standard torque values off the internet. These values are based on steel to steel joints and on our old bikes one side of the joint is steel to old aluminum cast material. The pull out force for aluminum threads is lower then steel.   

[SUPERTUNE]

Stock RD studs will hold 22-24 ft-lbs no problem.
All 400's and only RD350's with 400 gasket conversion and most aftermarket heads.

But not on stock RD350 heads with oem ring head gaskets (18 ft-lbs max) especially shark fin heads, they will crack over 18 ft-lbs.
Chuck

[Jspooner]

I do 17 ft-lbs on all of them no matter what kind of gasket or if they have an o-ring.

[m in sc]

I would recommend caution when looking at standard torque values off the internet. These values are based on steel to steel joints and on our old bikes one side of the joint is steel to old aluminum cast material. The pull out force for aluminum threads is lower then steel.

True,
but that also depends up how much engagement they have. rd studs onto cyls and the head bolts are not standard, they are about 2x what the values are based on for a steel fastener.

you are correct with regular nuts and bolts, for sure, and it should be noted. however, the stud engagement is at play here.

fwiw, i have -never- had one pull out at that value.