re: any diesel powered vehicle- (if designed properly) comes with a "compression
release" lever or mechanism to hang the valves open,,,,

As my MCC is stillll at MCR.... please explain?

Jake brake
Now I know! Thanks Tom

The only engine, in a truck, that I'm aware of was the Cummins 855 Engine. These were in big rig trucks that were 35+ years old. They were probably in on other engine makes, but I'm not familiar with them.

You would pull a mechanic lever and then crank the engine over. Because the valves were held open, the engine had no compression and could turn over at a good clip. Once spinning, you would release the lever and the engine would fire off and start up. Great for cold weather ignition.

I know they were also used on some earlier era, larger displacement engine found in motorcycles and trikes. I believe that the engines in piston aircraft, the ones that used the shotgun blasting caps to start, also had compression release levers on them too. Seeing that we have a few aircraft enthusiast on our boards, perhaps they would know.

But the statement... "any diesel powered vehicle- (if designed properly) comes with a "compression release" lever or mechanism to hang the valves open" I would have issue with. That's like saying, "Any properly designed car should have an AM Radio"

Tom's linkage to an exhaust brake is still technically a "Compression Release Device" but in reality it causes compression in an engine and then releases it at a different time so there is no power stroke. These "Engine Brakes" used oil galleries to funnel oil psi to an electric tappet type of piston that held the exhaust valves open. This makes the engine into a big air compressor. As far as I know, they never had a lever or mechanism to hang the valves open" like you described.

quote:

I know they were used on some earlier era, larger displacement engine found in motorcycles and trikes.

Quite a few of my vintage two stroke bikes through the years had compression release levers. Because two strokes fire on each piston stroke, they can be difficult to kick start compared to a four stroke where you can get the engine spinning if the kick lever is positioned properly. At some point the manufacturers built the compression release into the kick start (or electric start) to make it more user friendly.

On a two stroke the compression release is nothing more than a pop off cylinder valve controlled by a cable. It was really fun when you forgot to pull the release on a 450/500cc two stroke. The result of you effort was often launching your body off the bike when the kick lever refused to budge and you were kicking with all your might. I once left my bike in the middle of a raging spring stream propped up on a rock while I retreated to the bank to rest. It was a comical sight with the bike in the middle of the torrent, riderless, water spraying five feet high off the front tire! Meanwhile, I was fighting back a heart attack laying exhausted on the muddy river bank. And you though RVers had all the fun

No truck diesels that I remember. If I remember correctly the old CAT D8 had a gas engine to start the big engine.

This goes back 50+ years but if memory serves me

Start the gas engine.

Pull the compression release on the diesel
through clutch from little gas engine to biggy diesel

When biggy diesel is spinning nicely push the compression release back in and if you are lucky you the big engine starts before the little engine dies.



+

Gary, I have a friend with a JD 70 tractor that has a little 4 cylinder gas pony motor to start the diesel engine. It was one of the few diesels that would start in the cold weather. If the pony motor would start you had all the cranking power you needed.

I don't remember the 70 having compression release. His JD A did but it was a gasser. You could always count on the Johnny Popper to start no matter what the weather. It amazed me that a crank started tractor built in the 30's could be such a reliable machine.

It would seem to me that a compression release on a diesel would only be to get it spinning. Since it uses compression to ignite the air/fuel mixture, it would need to compress to finally start.

Back in the dark ages when i first started running equipment i ran a few that had the pony motor or the compression release on them. Also ran one that had a hand crank like a model T. Not a lot of fun trying to start that one in cold weather.

quote:

Originally posted by Moonbeam-Express:

Quite a few of my vintage two stroke bikes through the years had compression release levers.

A lot of four stroke singles had them, too. To ease the piston just past TDC on the compression stroke to get the full flywheel effect from the kick. A manual spark retard also helped, lessening the chance of kickback.

quote:

Because two strokes fire on each piston stroke, they can be difficult to kick start.

I had a coupla hot two strokes that would kick back and start up backwards if the kick was not sufficiently vigorous. The first time this happened was a little dramatic. I learned by the sound and roughness that it was running backward and avoided drama from then on. I learned to ride my Husky 400 backward just as a stunt. Never learned to turn, though.

quote:

On a two stroke the compression release is nothing more than a pop off cylinder valve controlled by a cable.

On the four strokes, it just put some pressure on the exhaust valve to open it a little.

quote:

It was really fun when you forgot to pull the release on a 450/500cc two stroke. The result of you effort was often launching your body off the bike when the kick lever refused to budge and you were kicking with all your might.

My Husky 400 did not have a CR, but my bulk and those wonderful Full Bore boots always convinced it to turn over and fire.

I had a friend with a DBD34 who did not use the compression release properly, and ended up with a broken foot. Another friend and I used to practice starting his Matchless 500 with one hand. We both won a lot of beers doing that.

I had a CR500 that put a hole through my boots. Don't know if it broke my foot, but there were weeks I couldn't ride it because I was too sore to start it. I would switch foots to spread the pain. Hard starting off side!

Comparatively, my KTM 300 is almost the same HP, 1/3 less weight, and starts on one mild kick every time. This is when technology works!!!

quote:

Originally posted by Moonbeam-Express:
Hard starting off side!

When my right knee, foot or ankle was acting up, I would attempt to use the left foot to start a RH kick bike. Never got the hang of it. Dropped the bike a few times.

I had an OK Cub diesel that had adustable compression ratio. Lower it for starting, then adjust it for smooth running.