Compression Relief Valve

[JohnS]

Paddy,

I dont believe that is a good analogy. In this case we have the whole engine recipricating assemblies moving, and then just adding compression. I would say, dropping the clutch is more equivelent to the initial load the starter sees, without decompression.

 

[joerocker]

Greg,

So, you're saying that the CR is MEANT to be used every time you start it? I had always thought it was only for cold...VERY cold weather starting. Hmmm, makes sense though. Get everything flowing and pressurized before actually "loading" it by running the engine...I just wasn't sure how much of a difference it actually made. If it's designed to work that way...well then I'm going to do it that way!

bluechip,

Excellent description! You convinced me! I'll start using the CR every time I start it. I didn't know they had a nice beefy flywheel to keep that "angular momentum" going to help the starter during that "slam" when you close the CR back up.

I learn more and more every day from you guys!!!

I love the internet...

 

[Paddy]

Maybe you didn't understand my post. Yes, the starter sees the full load with compression. The fly wheel on a tractor is huge and thus angular momentom. By using the decompression you get the momentom going very easy. This saves starters. It starts fast under almost no load on the starter.

 

[greg_g]

</font><font color="blue" class="small">( Greg,
So, you're saying that the CR is MEANT to be used every time you start it? )</font>

No. I said " every time I start a cold engine ", meaning an engine that hasn't yet been started that day. All the oil has long since drained back into the sump. Very cold days often require its use upon RE-starting as well.

//greg//

 

[TruChaos]

I had the chance to bend the ear of a PhD Mechanical engineer who used to work for Ford. He now teaches engine design.

I asked him about the compression release issue and a few others. Here's what he said.

He said that yes, the compression release greatly reduces the mechanical load on the starting system. Also, since the engine isn't experiencing compression when the compression release is used, spinning it to prelube the bearing should provide a significant reduction in wear regardless of temperature. He said that the bulk of engine bearing wear in all engines occurs during the first half dozen revolutions. Eliminating compression during these first few revolutions should greatly reduce bearing wear until the pump gets oil to them.

 

[joerocker]

Chaos,

Thanks...I was waiting for words like that..."greatly", "significant", etc.

I had always though it was just for really cold weather starting. The others convinced me to use the CR and you reinforced it.