let's have another update - after quite some time!
preludeas i said, i had my doubts about the cam. to exclude any errors on my part or with my equipment, i brought it to my local shop together with the timing card and just told them to install it. when it was time to pick it up the mechanic just shook his head and said he doesn't know what's going, just can't get it right. he had some numbers noted down on the card - which pretty much matched my previous measurements.
act 1so i called megacycle and had a good long chat with barbara. she asked me to send my numbers. by fax. because they're stuck in the mid-20th century and don't use email. now who has a fax machine at home? well this being the 21st century i found some internet service through which i could send a fax for free, so that was sorted - phew!
my numbers that i sent in:
Intake:
Open – 27 BTC
Close – 49 ABC
Lift - .275”
Duration - 256
Exhaust:
Open – 77 BBC
Close – 49 ATC
Lift – .275”
Duration - 306
these were measured as the timing card suggests, with 0 lash at .040" lift.
according to the same card, the numbers for the 12600 cam should be:
Intake:
Open – 11 BTC
Close – 50 ABC
Lift - .285”
Duration - 241
Lobe centre - 109.5
Exhaust:
Open – 51 BBC
Close – 10 ATC
Lift – .270”
Duration - 241
Lobe centre - 110.5
that's nowhere close.
act 2called them again after sending the fax. barbara saw that the numbers were off and passed me on to jim (the owner?) who also agreed that they didn't seem right and that he would replace the cam if it was really wrong. he asked me to measure once more, however, with the following method:
- valve lash set to 1mm (.040”) on in/ex
- degree wheel setup, rotate engine forward until lash starts to take up (tightens)
- put a mark on degree wheel = opening point
- proceed rotating forward until lash starts to take up (loosens)
- mark on degree wheel = closing point
- calculate 1/2 way point between these marks
then send him the numbers and a photo of the degree wheel with the markings. by fax, of course.
act 3so i went and did this, and here's what i got:
Intake:
Open – 19 BTC
Close – 42 ABC
Duration: 241
Lobe centre: 101.5
Exhaust:
Open – 52 BBC
Close – 12 ATC
Duration: 244
Lobe centre: 110
guess what? exhaust is pretty much spot on, and intake is only slightly different from the timing card.
looks like the cam will be good, after all. it’s still a mystery to me how both i and the shop mechanic came up with such different numbers when measuring with the dial gauge. i can only guess that there is some variation in the cam or in the system that’s being evened out by the more tolerant manual method.
i called jim and gave him these numbers. in his opinion the cam should work well. so that's it, i'll put my doubts aside and give it a go.
epiloguei shared the whole story with mike who also found it interesting that jim's method would give such better numbers. he suggested to time it again at running clearance.
so when i do this i'll have used three methods and just use the one that gets me closest to the timing card, ignoring the rest? so much for this being an exact science. anyway, i'm glad i'm getting somewhat closer to the truth now
