Camshaft, am I missing something?

[GreenLight]

I took this engine (Tecumseh HS40) apart nearly 10 years ago and have no memory of the disassembly process.

Anyways, the repair manual talks of a component called the "compression release mechanism" on some engines and as there is a hole machined into the gear (see below) I'm concerned that I may be over looking something/missing a part. Any info is appreciated.

 

[jeep2003]

it depends what year i think depending how the compression relase is achieved. that looks like a regular cam to me. check the backside of the exhaust lobe it should have a very shallow lobe. That is your compression release on the older motors. lots of guys actually grind that lobe off because it lowers your compression at all rpms

 

[boristheblade]

You do not have a compression release.
It's a little spring loaded doo dad.
Hole is probably drilled for balance.
Carry on.

 

[GreenLight]

Thank you, sirs.

 

[badtec]

it depends what year i think depending how the compression relase is achieved. that looks like a regular cam to me. check the backside of the exhaust lobe it should have a very shallow lobe. That is your compression release on the older motors. lots of guys actually grind that lobe off because it lowers your compression at all rpms

A compression release does NOT lower your compression at all RPM's. It only works on start-up.

 

[jeep2003]

A compression release does NOT lower your compression at all RPM's. It only works on start-up.

how does it not? its formed into the cam lobe. unless im forgetting something

 

[C9H13NO3]

how does it not? its formed into the cam lobe. unless im forgetting something

I don't know about this engine but clones have one that is RPM activated and de-activated.

 

[jeep2003]

I don't know about this engine but clones have one that is RPM activated and de-activated.

yea mostly all newer engines do but the old engines and the cam pictured have a small lobe on the oposite side of the main lobes to realeas some pressure during compression. Theres no way that i can see that that is voided during higher rpms

 

[C9H13NO3]

Ok I see what you mean now. Maybe it is less effective at higher rpm's?

 

[jeep2003]

well i think they probrobly changed that design because dumping raw fuel isnt exactly environmentally freindly. and the new design made it even easier to pull and more compression and hp. honestly i wonder why they couldnt come up with a better design than that :shrug:

 

[jreid50]

Actually at higher RPMs the ignition will actually retard itself, so the performance isnt really effected! And with the overlap and the exhaust scavenging effect it really doesnt waste much fuel! Just a thought!