New Question on Briggs 17.5 HP, OHV Engine

brchad

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Well.... the old fart is back..... this time with a trivial question perhaps!

Engine Model 31C707-3346-G6 (Now running again!) It's a OHV .... Boobala! :laughing:

I can't seem to get this part of my rebuild out of my mind. This may have come up on other threads.... if so .... sorry for the duplication.

It involves this part.... which is a restrictor gasket, metal front with soft gasket back combined.... that goes where the intake tube bolts to the head:

768.jpg

Can anyone tell me WHY it's there? What is it doing other than reducing potential power? I thought about taking it out and simply using the standard gasket but the tube uses an O-ring... and how would that seat against the soft gasket. Perhaps leave out ALL flat gaskets and mount the O-Ring tube directly to the head? Maybe cut the restriction out making it a perfect circle instead and reinstall?

Thoughts anyone?
 

BlazNT

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Ok, so that is an optional part. If you did not have it during the tear down then it should not be installed. If you did have it before then your engine is designed to have it.
 

bertsmobile1

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Well.... the old fart is back..... this time with a trivial question perhaps!

Engine Model 31C707-3346-G6 (Now running again!) It's a OHV .... Boobala! :laughing:

I can't seem to get this part of my rebuild out of my mind. This may have come up on other threads.... if so .... sorry for the duplication.

It involves this part.... which is a restrictor gasket, metal front with soft gasket back combined.... that goes where the intake tube bolts to the head:

View attachment 34980

Can anyone tell me WHY it's there? What is it doing other than reducing potential power? I thought about taking it out and simply using the standard gasket but the tube uses an O-ring... and how would that seat against the soft gasket. Perhaps leave out ALL flat gaskets and mount the O-Ring tube directly to the head? Maybe cut the restriction out making it a perfect circle instead and reinstall?

Thoughts anyone?

That is exactly what it is doing, restricting the power output to 17.5 Hp.
It is all about costs.
The mower companies design a mower, and work out the power required to run it.
They then get quotes for an engine that is 125 % of that figure with a minimum operating hours of X and a continious operating time of Y Hours and generally a price range.
The cheapest thing to do is to stop down an existing engine
The first 2 numbers is the capacity in Cu inches, in your case 31 cubes
That same engine comes out in 5 Hp ratings and the only difference will be the restrictor plate, governor spring & carb jetting.

This is why the parts books never mention Hp.
If you walk around a mower shop and look at the model numbers of all the engines you will see this.
The Husqvarna will have the engine rated at 21Hp while the identical Craftsman will have the same engine rated at 19Hp.

Honda do exactly the same thing with the composite inlet manifolds.

No one could afford to manufacture 40 engines from 10Hp to 30Hp in 1/2 Hp increments with each one using a different bore & stroke there would not be the economies of scale.

So if you want to get right into it, find the largest HP rated 310000 engine, download the parts book and check which bits have different part numbers to your 17.5 Hp, swap those and you have just upped the HP & FUEL CONSUMPTION of your engine.

In most cases all it will do is gobble more fuel as the equipment is already over powered and the bigger engine runs at exactly the same speed.
If you regularly run your gear way over the design limits , like regularly cutting grass that is 14" tall or try to bag leaves that are 2' thick on the ground, or cut wet grass regularly then the increased Hp might do some good but generally all is does is use more fuel and in the worst cases break belts.
 

Boobala

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I see it THIS way, IF your engine is running as well (or better ) since your rebuild, and you are satisfied, leave it alone, OR, to quote an old phrase, if it works,... DON'T fix it !! ..IF YOUR engine is running well, you're better off than most people seeking help on this site !! ..:thumbsup:
 

ILENGINE

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That is exactly what it is doing, restricting the power output to 17.5 Hp.
It is all about costs.
The mower companies design a mower, and work out the power required to run it.
They then get quotes for an engine that is 125 % of that figure with a minimum operating hours of X and a continious operating time of Y Hours and generally a price range.
The cheapest thing to do is to stop down an existing engine
The first 2 numbers is the capacity in Cu inches, in your case 31 cubes
That same engine comes out in 5 Hp ratings and the only difference will be the restrictor plate, governor spring & carb jetting.

This is why the parts books never mention Hp.
If you walk around a mower shop and look at the model numbers of all the engines you will see this.
The Husqvarna will have the engine rated at 21Hp while the identical Craftsman will have the same engine rated at 19Hp.

Honda do exactly the same thing with the composite inlet manifolds.

No one could afford to manufacture 40 engines from 10Hp to 30Hp in 1/2 Hp increments with each one using a different bore & stroke there would not be the economies of scale.

So if you want to get right into it, find the largest HP rated 310000 engine, download the parts book and check which bits have different part numbers to your 17.5 Hp, swap those and you have just upped the HP & FUEL CONSUMPTION of your engine.

In most cases all it will do is gobble more fuel as the equipment is already over powered and the bigger engine runs at exactly the same speed.
If you regularly run your gear way over the design limits , like regularly cutting grass that is 14" tall or try to bag leaves that are 2' thick on the ground, or cut wet grass regularly then the increased Hp might do some good but generally all is does is use more fuel and in the worst cases break belts.

That may or may not be accurate. Parts used on the production line may or may not be the same as the replacement parts. For example a camshaft that is used on say a 19.5 hp may be different than what is used on a 21.5 hp engine, but the replacement camshaft for both may be the camshaft that was used on the production 20.5 hp engine.
 
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