bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
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The head is tested for warping , erosion & thread pulling .
Warping is done corner to corner and is very rare on a mower head
Erosion is quite common because the gasket starts to leak and the movement of gas , particularly burning gas erodes the metal from both the head & the block, exactly the same way a river erodes a valley or canyon.
On Inteks the bridge region between the push rod tunnel & cylinder is where it usually erodes.
Then we come to thread pulling
Run a short strait edge across all of the holes in the block
Usually you fund the metal has raised slightly at the edge of the holes
This happens because there is a tiny annulus of the block that has no support when the pressure is applied because the head gaskets are not a tight fit on the engine bolts .
The head can do the same thing but usually the hole just collapses onto the bolt which is why some times the head bolts will not pull out easily.
Using a thick large diameter washer avoids this because it spreads the load over a larger area and thus only the shear plane is massively larger .
For those who have tried to flatten an intek head and block the first thing you will notice is while it is flat, it is not smooth and on the first couple of strokes you reveal the tooling swirls from the fly cutter used to machine them at the factory.
Do not try to remove them completely they are there to prevent the gasket from walking under pressure
Now we come to torque
People will argue to the ends of earth weather they should be 21 ft lbs or 22 ft lbs etc etc etc
It does not make a wrinkled rats rectum of difference
Anything from around 15 ft lbs to 30 ft lbs is fine
15 is where the clamping force is no longer enough to hold the surfaces tight enough to resist the gas pressure during combustion .
30 is approaching the yield strength of the alloy threads in that diameter bolt .
What is vital which all the Face Book experts fail to appreciate is that ALL THE TORQUES ARE IDENTICAL.
This is why B & S Started to use in lbs in place of the usual ft lbs
when they say 240 in lbs that is 240 +/- 0.5 in lbs so they expect you to do those bolts up to within 1 in lb of each other .
This implied accuracy is what every one fails to understand
a tension wrench marked in in lbs only will be a lot more accurate than one marked in ft lbs only and thus a lot more expensive
If they specified 20 ft lbs again that is +/- 0.5 ft lb with is 12 in lbs and no where near as accurate or in this case consistent and consistency is why you are shooting for for not absolute accuracy .
and when it come to accuracy, very few torque wrenches under $ 100 will be accurate and of those that are they only read true over a limited temperature range and micrometer adjusted ones go out of calibration very quickly even if you back them all off past zero every time you have finished using them because the internal coil spring collapses with use , same as your car suspension springs sag or valve springs shorten over time .
Next we come to the actual tightening
the more steps the better ( within reason ) so torquing them in 3 or 4 steps will always yield a better result then hand tight then final torque .
Finally a full copper head gasket has copper all the way from the cylinder to the outside world
a std B & S gasket has nothing more than the very thin fire ring ( if that ) to hold back the combustion gasses .
Once that is breached then you have a composite layered joining board and that does not have the structural integrity to stop leaking between the layers
So go with Lanni's full copper gasket & it will be a last time you have to do the job, if you do it properly
FWIW I use a1/2" drill bit hand held to cut a tiny champher around all the bolt holes
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