6 replies to this topic

[Kyle Freiheit]

Hey all,

  Measured a bunch intake and exhaust valve springs today and I am confused. My setup reads in PSI(40-45psi for intakes and 30-35psi for exhausts). 

 

My 1.6L FSM lists the spring pressure(tension?) 228 Nm @ 1.575"(Closed). It also has that listed in 23.3 m/kg and 168 ft/lbs. Not sure how Mazda thought it was a good idea to list this measurement like that. I can't for the life of me figure out how to do this conversion. Any ideas?

 

 I read a little online that some FSMs may actually have a PSI reading. Anyone want to have a look? Engine builders want to poke me in the right direction?

 

Kyle

[Jim Boemler]

My manual reads the same as yours.  None of these scales (including PSI) seem to make any sense for what should be a pure force or weight measurement.  Does your setup use a piston of known diameter, from which you calculate a force?

[Kyle Freiheit]

Jim,

  Thanks for checking. Looks like the units are built/calibrated to read in PSI but its the actual force(Lbs). Must have a 1 sq in. piston. I stood on it last night and it was right on my weight.

 

Looks like the book spec is a spring rate(168 ft lbs = 2016 in lbs). These springs are fairly progressive but I imagine I could measure the forces for the middle 50% of its range and calculate the rate from that but it still leaves more questions than answers.

 

Kyle

[Kyle Freiheit]

Glad I can make things tough on myself. Checked the Technical Data section in the back of the book and it has all the info. For those that are looking for this info in the future. 

 

1.6 Miata

Free Length Intake- 48mm(1.893")

Length Intake Spring @ 40mm with a set load of 23.3kg(+1.75 or -1.17kg)

Setting Load Height @ 40mm(1.575")-  22.1-25.1Kg (48.6 - 55.2 lbs)

 

Free Length Exhaust- 48.3mm(1.902")

Length Exhaust Spring @ 40mm with a set load of 18.6kg(+1.4 or -.93kg)

Setting Load Height @ 40mm(1.575")-  17.7-20kg (38.9-44lbs)

[Jim Boemler]

These springs are fairly progressive but I imagine I could measure the forces for the middle 50% of its range and calculate the rate from that but it still leaves more questions than answers.

The instructions seem to say to apply the stated force, and check that the spring height is greater than or equal to 40mm.  That side-steps the issue of "rate" entirely.

[Kyle Freiheit]

Yep. Not sure what the heck they were thinking when they wrote the spec in the inspection explanation. When you look at the spec in the back of the book, it makes sense. 

 

Kyle

[Kyle Freiheit]

Seeing as we can't shim valve springs to bring back lost seat pressure(As described in FSM). What's everyone doing? New Springs? Get a matched set even if they are on the low side? Has anyone seen any evidence of valve float on worn out motors?

 

Thoughts? 

 

Kyle

 

PS: Last time I refreshed this head, I just checked them for free length and if they were square but I guess I am wondering if there any gains by going with a little more seat pressure.