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Zetec piston to valve clearance???
norm007 - 18/11/09 at 02:54 PM

Hi.
I am building a 2.0 silvertop Zetec engine with Piper 285 cams and a flowed head.

I have dropped my head off to have it skimmed, but I forgot to check piston to valve clearance 1st.
I have asked for a 30thou/0.75 skim to give me 10.3 - 1 ratio.

My question is, does anybody know if I will have valve/piston contact at 30thou/0.75mm???

Thank you in advance

will121 - 18/11/09 at 03:23 PM

the 285 cam has quite a lot of lift, but not seen anywhere requirement for piston mods, a call to Piper or Burton power might be an idea to confirm. did you caculate CR as from the link below seems to indicate 20" skim give increase of CR to 10.6/1. b but not tested it myself to check.

C/R calc link

Chippy - 18/11/09 at 03:24 PM

Do a dry build of the engine, putting some plastacine, (sp) on top of the pistons in the area of the valves, turn the engine over, take of the head and measure the thickness of the plastacine. HTH Ray

MikeRJ - 18/11/09 at 04:03 PM

quote:
Originally posted by Chippy
Do a dry build of the engine, putting some plastacine, (sp) on top of the pistons in the area of the valves, turn the engine over, take of the head and measure the thickness of the plastacine. HTH Ray


Hydraulic lifters make this a bit tricky, you really need to replace them with solid lifters to make this measurement accurately.

norm007 - 18/11/09 at 04:06 PM

did you caculate CR as from the link below seems to indicate 20" skim give increase of CR to 10.6/1. b but not tested it myself to check.
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Thanks for the advice/link.

I have just gone through my calculations again and you are right.
I have just rung machine shop to advise a 20thou skim instead of 30thou.

will121 - 18/11/09 at 05:50 PM

quote:
Originally posted by norm007

Thanks for the advice/link.

I have just gone through my calculations again and you are right.
I have just rung machine shop to advise a 20thou skim instead of 30thou.

20thou is what im going for, is it a profesional ported head, as im doing the DIY route, have you got any pictures of your ports?





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[Edited on 18/11/09 by will121]

Dusty - 18/11/09 at 08:18 PM

I did 20 thou skim and used piper 285 cams. Had to machine slots for the cam lobes beside the followers as their peaks hit the head casting. Piper said this was not common but had been reported before. No problems with valve piston clearance.

norm007 - 20/11/09 at 03:06 AM

20thou is what im going for, is it a profesional ported head, as im doing the DIY route, have you got any pictures of your ports?---------------------------------------------------------------------------------------------------------------
Mine is also a DIY job. When I get the head back I will post some photo`s




.

[Edited on 18/11/09 by will121]

will121 - 23/11/09 at 09:30 PM

pictures of mine