3VZ-FE Head Skimming & Compression Ratios

[cdwood2010]

Will the inlet manifold still sit properly in the V with that big a skim?

I was wondering about that. Had a look at one in the garage, and they bolt down vertically rather than to the head sides. I think at the worst it might be on the edges of the threads, but I guess we'll find out when he bolts it all together!

C.

[wood_patrick]

Adam, muchos gracios on the figures. I was hoping you could help me out on them. :-)

1mm/1* change I can cope with for this, and I will check measurements when I get an assembled block in front of me and update.

With the v-bank I'm hoping the bolts still line up but I've got a die grinder at the ready to remove any lips/steps that need altering post skim between the heads and v bank. If the bolt holes need altering/elongating then a quick trip to the machine shop will be in order but I'm hoping it won't be necessary. :-)

Should have the heads stripped for machining over the weekend and be taking them down on Monday/Tuesday.

[wood_patrick]

Also Adam, with a 1mm skim the heads timing between them is altered by 1mm/1* as you calculated.

How do you anticipate the first cam changes from the crank? Based on your calculations I would expect that to be similar and if so how much (for future reference) would the pulley sizes need to be altered by to compensate and maintain their original positions?

The pulley between the heads would need to be just under 1mm larger I would expect to compensate for the slack but I know the pulley above the crank would need to be a bit more to compensate for the 1mm slack due its angle... :-/

[headcase]

You do realize you may have vavle to piston trouble as well as you are moving them in closer . You need to know how far out the vavles are measured the overlap you may have to have the vavles seated back in to the head or cut more out piston .

[wood_patrick]

Yep. Well planning to do some measurements and also valves are being re-grinded too but fair point. Will get stuff measured before the skim. :-)

[adamh]

I was wondering about that. Had a look at one in the garage, and they bolt down vertically rather than to the head sides. I think at the worst it might be on the edges of the threads, but I guess we'll find out when he bolts it all together!

C.

if you have one in lair can you measure crank centre to camshaft pulley centre please :-). and one cam pulley centre to other

[HurleyRaceEngineering]

You do realize you may have vavle to piston trouble as well as you are moving them in closer . You need to know how far out the vavles are measured the overlap you may have to have the vavles seated back in to the head or cut more out piston .

Agreed 40 thou is a lot to be taking off the head(s)

Who is doing re facing of the valves for you? I presume you will be re-cutting the seats too?

[wood_patrick]

I agree completely that 40 thou is a lot to take off, but, I'm confident the bottom half of the engine will cope and the worst case scenario (I hope) is that it buggers up a set of heads.

That said though I really don't want to blow a set of heads if i can help it and if the chances are not in my favour at that much of an increase then I will go for lower...

Maybe starting at 40 thou is a bit brave especially without seeing what difference a smaller skim makes. Do you think a 20 thou would be better to try? :-/ Would welcome any input as my grasp of the internals and after effects of a skim are relatively limited.

[wood_patrick]

And valve faces I haven't thought or planned to do anything to as yet, but I have got access to a valve seat grinder thing that looks like a doctor who prop along with someone competent to use it. :-)

[adamh]

Also Adam, with a 1mm skim the heads timing between them is altered by 1mm/1* as you calculated.

How do you anticipate the first cam changes from the crank?

1/2 degree each. (0.5mm index at radius of cam pulley)

Based on your calculations I would expect that to be similar and if so how much (for future reference) would the pulley sizes need to be altered by to compensate and maintain their original positions?

if cam pulley was plus one tooth at (guess) approx 8mm pitch it would increase the radius at pulley by approx 1.27mm , which is almost perfect, but,
then you have a problem with the crank timing pulley because its a 2:1 ratio with the cams . so if changing pulley size you need change timing pulley on crank also to retain that ratio otherwise it would run like shit :-) or use trigger wheel ign on crank, and remove dizzy.

i think if you found an idler which was more than a few mm smaller like...1/4" on O.D smaller, you could shrink 1/8 wall steel sleeve on + 2mm on original O.D, and it would put the cams back in the original position to eachother. if the cams at the top are in correct relation, then the bottom does not matter the pulley above the crank is hydraulic it will fix any tiny error.

The pulley between the heads would need to be just under 1mm larger I would expect to compensate for the slack but I know the pulley above the crank would need to be a bit more to compensate for the 1mm slack due its angle... :-/

1/2 degree out cant be to bad even without a sleeved idler? maybe someone who has buggered with cam timing on a dyno can comment about 1/2 degree