It's a Hemi

[Nickolas]

Hey,
I was doing some digging and found some original literature on the Homelite Super XL-925 and come to find out it has a Hemi Head on it. I never heard of a chainsaw with a hemispherical combustion chamber. No wonder it has the power it does. Anyone else heard of Hemi head chainsaws? This is new to me... Here is a direct copy and paste from the booklet...


"ENGINE
--
Type: Homelite 2-cycle, single cylinder, air cooled, loop
scavenged, made of light alloys. Hemi-head cylinder and
hi-flow transfer ports for greater efficiency and more power.
Top guided connecting rod, wide spaced, twin piston rings,
large volume cooling air flow for longer life under heavy
duty use. New Wear Guard'"' specially plated cylinder
virtually eliminates cylinder bore wear.
Dry Weight: 16.71bs. (7.6 Kg.) .
Displacement: 5.00 cu. in. (82 cm3 )
Bore: 2.06 in. (5.2 mm.)
Stroke: 1.50 in. (3.8 mm.)
Speed: 8,000 rpm. at max. hp."

 

[barneyrb]

Hey,
I was doing some digging and found some original literature on the Homelite Super XL-925 and come to find out it has a Hemi Head on it. I never heard of a chainsaw with a hemispherical combustion chamber. No wonder it has the power it does. Anyone else heard of Hemi head chainsaws? This is new to me... Here is a direct copy and paste from the booklet...


"ENGINE
--
Type: Homelite 2-cycle, single cylinder, air cooled, loop
scavenged, made of light alloys. Hemi-head cylinder and
hi-flow transfer ports for greater efficiency and more power.
Top guided connecting rod, wide spaced, twin piston rings,
large volume cooling air flow for longer life under heavy
duty use. New Wear Guard'"' specially plated cylinder
virtually eliminates cylinder bore wear.
Dry Weight: 16.71bs. (7.6 Kg.) .
Displacement: 5.00 cu. in. (82 cm3 )
Bore: 2.06 in. (5.2 mm.)
Stroke: 1.50 in. (3.8 mm.)
Speed: 8,000 rpm. at max. hp."

All saws I know of are a "Hemi" or "Semi-Hemi" design. There is no place but up top for the plug to go.......

 

[GBD]

All saws I know of are a "Hemi" or "Semi-Hemi" design. There is no place but up top for the plug to go.......

Some have "bathtub"...

 

[cpr]

Every one I've ever been in was a semi-hemi except the Power Products. It's a flathead.

 

[kevin j]

'Hemi' used to mean the original chrysler V8s of the 50's, then of the 60's. The head was hemi shaped and one valve on each side intake and exhaust, with plug in the middle at fully TDC. It allowed larger valves, straighter ports, and better air flow, and better combustion with the centered plug, higher compression without detonation.

the 'normal' V8 was/is valves side by side and the plug off to one side. One or the other of the ports has a kink in it as it changes direction.

Chrysler had done some brilliant marketing and trademarking. Most people associate 'hemi' with awesome mystical power, but have no clue why or if it really matters.. Many engines now are 'hemi' shaped. Dual overhead cams have the I and E separated and plug in between. Even many single overhead cam engines have an extra set of rockers and have the valves pretty well separated, with I and E ports very straight and good breathing.

Two cycles (well saws anyway) don't have valves, so the term hemi is technically true, but meaningless.

 

[GBD]

Every one I've ever been in was a semi-hemi except the Power Products. It's a flathead.

Stihl 075/076 have "bathtub", and I suspect 051 and maybe 041 have it, too. At least some Husky 185 cylinders have it, as I have seen one that has.

 

[GBD]

'Hemi' used to mean the original chrysler V8s of the 50's, then of the 60's. The head was hemi shaped and one valve on each side intake and exhaust, with plug in the middle at fully TDC. It allowed larger valves, straighter ports, and better air flow, and better combustion with the centered plug, higher compression without detonation.

the 'normal' V8 was/is valves side by side and the plug off to one side. One or the other of the ports has a kink in it as it changes direction.

Chrysler had done some brilliant marketing and trademarking. Most people associate 'hemi' with awesome mystical power, but have no clue why or if it really matters.. Many engines now are 'hemi' shaped. Dual overhead cams have the I and E separated and plug in between. Even many single overhead cam engines have an extra set of rockers and have the valves pretty well separated, with I and E ports very straight and good breathing.

Two cycles (well saws anyway) don't have valves, so the term hemi is technically true, but meaningless.

Real "hemi" fourstroke chambers are long gone because of their lack of ability fight "knocking". They were far from compact, and offered little or no squish effect. Modern fourstroke heads with angled valves are of shallow angle "pent roof" design with flattop pistons and generous squish areas.

 

[CTYank]

Real "hemi" fourstroke chambers are long gone because of their lack of ability fight "knocking". They were far from compact, and offered little or no squish effect. Modern fourstroke heads with angled valves are of shallow angle "pent roof" design with flattop pistons and generous squish areas.

True MoPar hemis had loooong flame travel. Heads made great boat anchors, too.

Pent-roof showed up IIRC with 4-valve twin-cams like 3-liter Cosworth-Ford in F1, and it was all over. Relatively speaking, hemis suck wind. Short flame-travel and large flow area with multiple valves at low lift and duration close the casket on the hemis and successors.

 

[homelitejim]

The entire 10X series of McCulloch all have a hemi combustion chamber.

 

[lesorubcheek]

Not sure what Homelite's first "hemi" was, but I'm guessing it started with them back in late 60s or early 70s. Basis for this is the 2000/2100 cylinders. Top of a 2000 is relatively flat with a recess for the plug. The 2100 though had a dome. Another example is the XL1xx saws. 102,103s had a flat top. 123s though have a dome. These both point to that time frame.

Dan

 

[514mach1]

Just want to mention that even the new dodge hemi is not a hemi. It has quench pads... and would never pass emissions if it didn't. It's a two valve pent roof chamber. My good friend has an '09 dodge and he was bragging that it had a "hemi". I just said, "yep, that truck has a fine engine and it's not an actual hemi, thankfully."

 

[Tzed250]

The original Hemi heads were patterned after aviation designs. The 426 Race Hemi came out in '64, shortly followed by the street version. The engine dominated NHRA Superstock and later on Pro Stock, as well as NASCAR racing before the sanctioning bodies put a clamp on them. This success came from the ability to flow mega air through the huge valves and then light it off with the centrally located plug.


The Chrysler Hemi is still the basis for NHRA fuel classes.

 

[Nickolas]

Thats interesting I never gave it any thought. I was an auto mechanic for years but never took a chainsaw apart or read about the engine style. I'm familiar with the auto Hemi engines but not with chainsaw engines. I wish I knew back then what I know now... Not to get off topic but back in the early eighties I almost bought a 67 Plymouth GTX with factory 426 Hemi, automatic, Dana rear of course and 150 speedo if I remember correct. Man when he popped the hood I couldn't believe how big that Monster elephant motor was. That car was sweet and I almost bought it but for some reason I backed out of it. He wanted 9K for it back then. Also had a 68 Z28 for 6K and a few other muscle cars. I never thought about years ahead and how much these cars would go up in value.

I always have kicked myself in the rear for not getting that GTX. I already had about 5 muscle cars at the time so probably why I didn't get another but I wish I had and just stored it away all these years. Could you imagine driving a factory 67 Hemi GTX down the road now... I'd be smiling ear to ear. Some wouldn't drive it at all but I would have to sometimes. I couldn't just let it sit without being driven. Anyway It's interesting with a chainsaw Hemi engine it just never crossed my mind. That 925 does seem to have good power even with 125psi compression. After I get a different bar and some 404 semi chisel chain on it I think I will like it better. I still have a sweet spot for McCulloch and have a good case of yellow fever. Thanks for the info though about chainsaw motor designs it enlightened me a bit.

 

[mt.stalker]

Hemi simply means "half round" , in this case combustion chamber . They've been around, in various cars for 110 yrs. Chrysler had a 392 Hemi back in 1957 . Chainsaws have had hemi heads for a very long time .

 

[Tzed250]

Chrysler air raid siren. Powered by a 331 cu. in. Firepower Hemi.

Where's my Civil Defense helmet ??


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