High-boss vs Low-boss Cylinder Head ???

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BearKiller
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High-boss vs Low-boss Cylinder Head ???

Post by BearKiller »

Head-gasket blew and melted a channel in my head.

Now I find that there are two variants, High-boss and Low-boss, the difference being in the thickness of the head-bolt "boss" and length of head-bolts.

I am told that other than that, they will interchange.

My head-bolts are 1-1/2" long with a mere 3/8" protruding below the head.

My head-bolt "bosses" are 13/16" thick, with the top of the bolt being 3/16" below the top of the fins; I am told that this is a Low-boss head.

I have found a High-boss head, but I have no measurements as to boss thickness and head-bolt length.

I chased my bolt-holes and can thread 7/8" into the head; whereas, my current 1-1/2" bolts are only catching 3/8" : is 1-1/2" the original stock length for these bolts ?

Does anyone know the correct length head-bolt for a High-boss head ?

Please share any knowledge and experience you may have about these two different heads.

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>>>EDIT:>>> My head-bolts have lock-washers; the books do not show lock-washers; should I have or not have lock-washers ?
I have seven head-bolts and two studs; the books show four bolts and five studs; I see no reason for the other three studs; I am fairly certain that the seven/two arrangement is correct for the Cub Cadet, right ?

Thanks for reading and all help is appreciated.

BearKiller
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Re: High-boss vs Low-boss Cylinder Head ???

Post by BearKiller »

I found this:

http://gardentractorpullingtips.com/cylhead.htm

>>>Amended: According to what I have read thus far, my 1-1/2" bolts are correct for the head that I think I have, 4th Generation.

My spark-plug is directly over the exhaust valve.

The High-boss head is earlier and the Low-boss is supposed to run cooler.

JMotuzick
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Re: High-boss vs Low-boss Cylinder Head ???

Post by JMotuzick »

The 3 studs that are “extra”, are they along the flywheel side of the block? If so it’s posable that your engine was replaced with a short block or new engine for a narrow frame. Is your engine black from the factory? Often times the engines sold as replacement would fit many models if the changes required where minor like this.
No lock washers, just the heavy duty flat washers.
These 3 studs would be used to hold the gas tank mounting bracket down.

BearKiller
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Re: High-boss vs Low-boss Cylinder Head ???

Post by BearKiller »

JMotuzick wrote:
Tue Jul 14, 2020 9:46 am
The 3 studs that are “extra”, are they along the flywheel side of the block? If so it’s posable that your engine was replaced with a short block or new engine for a narrow frame. Is your engine black from the factory? Often times the engines sold as replacement would fit many models if the changes required where minor like this.
No lock washers, just the heavy duty flat washers.
These 3 studs would be used to hold the gas tank mounting bracket down.
Thanks.
Maybe my description about the bolts/studs was not clear enough.
There are nine holes.
The manual shows four bolts and five studs where I have seven bolts and two studs.
My gas tank has no part that attaches to the engine.
I guess the manual only pictures the style that does have the tank brackets, thus the confusion.

I sort of figured the lock-washers were something added by a previous owner.

I think I have found a good head identical to the one I have.

I am also going to have my aluminum welding friend to see if he can repair the bad spot and resurface the repaired head to keep for emergencies.

JMotuzick
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Re: High-boss vs Low-boss Cylinder Head ???

Post by JMotuzick »

Sounds like the manual shows the narrow frame only!?! No lock washers either way.

Klapatta
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Re: High-boss vs Low-boss Cylinder Head ???

Post by Klapatta »

A general rule of thumb when engaging threads into cast iron is one and one half times the diameter of the of the stud or bolt. More when ever possible. So a 3/8" bolt should protrude proud at least 9/16". Factor into this the thickness of the washers and head gasket as well. And yes,I totally agree with Joe, use heavy style SAE washers and no lock washers. That is what is specified. The three studs or bolts by the exhaust valve undergo the most expansion and contraction so I always bottom tap and try to hook as many threads as is possible while measuring to be sure that it does not bottom out. Different lengths can be marked with a sharpie or electric pencil.
Rarely do I ever mess around with second hand bolts in this area. After many heat and cool down cycles they are weakened.
I always use plenty of never seize too, you will thank yourself down the road when it ever becomes time to disassemble again.
I have heard that the low tower heads were meant to improve air circulation and can see that as a case in point. However with gas tank or shroud mounts involved that is not always possible.
Low tower heads that are heading to a high tower type setup can be made serviceable by making spacers as shown and that will work very well. Lesson learned here is never allow one to fall into the flywheel tin when installing!
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mortten
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Re: High-boss vs Low-boss Cylinder Head ???

Post by mortten »

The 2 studs go where the top baffle bolts down.

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Merk
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Re: High-boss vs Low-boss Cylinder Head ???

Post by Merk »

McMaster-Carr has a thick washers and spacers that work.

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