? about rebuilding a 2.25

[scott]

hey all, the motor i fried is all apart. damage was minimal and my machinist is ready to get to work

1. i've the 7:1 head. milling it down will raise the comp ratio. where can i find the the specs on how much i can shave off.

2. a 2.5 cam is better than a 2.25. my petrol was rebuilt by a po. how can i tell whether my cam, which is in great shape, is a 2.5 or a 2.25?

[Apis Mellifera]

1. -.100" is the rough estimation for milling a 7:1 head to 8:1. The only way to precise is to measure it and do some math, but that's close enough.


****As an aside, does anyone know if a factory 8:1 head can safely be milled to 9:1 (or more)?


2. I don't know the spec's for either cam, but you would compare lift and duration. I assume the 2.5 cam has more lift. Measuring the lift requires a dial indicator and a push rod if the cam is in the block or some V blocks if it's out. A fast and dirty way would be to put a caliper on the lobes, but you can't really accurately compare duration that way.

[scott]

greg of our host share some data with me

7:1 head is 3.69" thick
shave it to 3.59" you'll get 8:1
shave it to 3.54" you'll get close to if not 9:1
shave it any more you'll get a really big paper wieght

i've also heard that the lift duration is the same on the two cams. it's just that the 2.5 cam starts lifting earlier so you can adv the timing even mor and thus give you more power at the higher rpms but i still can't tell which cam i've got. its only marking is the word PETROL

[Linus Tremaine]

If you plan to mill the head, I strongly suggest that you find a later head rather than milling a 7.1:1. You can safely mill a 7.1:1 up to an 8.1 but beyond that is not generally thought of as a good idea by most of the more experienced people that I have spoken to. When I had my engine rebuilt I ran into this same question. I got a later head.