Jump to content

compression release


truth

Recommended Posts

checking if anyone has knowledge about how compression release handle works   heres my thinking    the lobes on #2 and 3 and 6 and 7 have 2 heights as the pictures show   so when the lever is pulled out the lobes hold valves open longer to aid in hand cranking   once started the handle goes to in position and allows all lobes to be the same?  i was starting to think the wear was on the cam but i think its made this way in order for compression realease to work or am i completely missing it?  pictures show typical 2 height lobe on cam [013 and also the yoke that slides the whole cam] 030 and 031 pics shows the distance the cam moves when operating the handle  [32 and 33 show same distance         thanks for any help  im a green horn working on a fiat tipo 55[american built]  sure would appreciate anyone w knowledge on this chiming in

fiat camshaft 013.JPG

fiat camshaft 030.JPG

fiat camshaft 031.JPG

fiat camshaft 032.JPG

fiat camshaft 033.JPG

Link to comment
Share on other sites

What is this on? Decompression releases have been around for many years. Since the first internal combustion engines were built. You photos are rather blurry, but I have seen similar systems on different applications. Old Caterpillar diesels for instance. Dandy Dave!  

Link to comment
Share on other sites

Early compression releases were just valves at the bottom of the cylinders that could be opened to vent the combustion chamber.  This is important to do before starting horizontally opposed two cylinder engines with old style oilers.  Excess oil continues to flow after the engine stops and can accumulate in the cylinders & cause hydraulic pressures that can crack the cylinder.  Compression releases allow the excess oil to drain while priming the cylinders with the fuel/air mix.  Cranking with ignition off and compression releases open solves this problem and primes the cylinders to fire when the ignition is turned on. 

Link to comment
Share on other sites

i probably wasnt as clear as i could on how this car is set up    there is a compression release handle on front of this car [pic]  when lever is pulled out the whole camshaft moves in the block and thus the rollers on the lifters are in line w the higher spot on the lobe    once it starts the lever is pushed in and all the rollers are now riding the same height on the front side of the lobe   i just assumed this was in practice during this era?   maybe fiat is the only car that had this type compression release for starting?im wondering if any other cars have this

compression release handle 001.JPG

compression release handle 002.JPG

compression release handle 005.JPG

Link to comment
Share on other sites

  • 2 months later...

Raised cams integral with the regular cams, and the camshaft (slides) endwise... without moving the timing gear.

 

So you're correct in understanding how it works. Explained at the bottom of page 1174 here -

 

http://books.google.com/books?id=8swqAAAAMAAJ&pg=PA1174&lpg=PA1174&dq=fiat+model+55&source=bl&ots=T3VrcyjLpE&sig=JPUZFxCpHS2GRM2o8C8_CAGMfdQ&hl=en&sa=X&ved=0ahUKEwihyoSg9MTNAhWIKGMKHfsHCKwQ6AEIKTAA#v=onepage&q=fiat model 55&f=false

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...