mcerd1
|
| posted on 15/7/16 at 11:58 AM |
|
|
Pinto rebuild - valve to piston clearance ?
I hope your all sitting down for this - but I've actually found some time to work on my car 
I figured it was about time to finish building the engine and one of the first jobs on the list was to check the valve to piston clearance
So I finished off the head, set the valve clearances, stuck it on with some plasticine on the pistons (using a spare gasket and belt)
then timed the cam with my dial gauge (which was nearly 8° off using the nearest tooth on the belt!) and turned it over a few times by hand, stripped
the head back off and measured the plasticine at a min of 2mm clear
its only at this point that I realised I don't know what the minimum acceptable clearance should be for these engines and despite searching for
some time now I can't find any conclusive answers 
the figures I've see range from just over 1mm (0.040" ) to more than 2.5mm - and some just say as much as possible.....
Any thoughts ?
-
|
|
|
|
|
Ian.C
|
| posted on 15/7/16 at 06:35 PM |
|
|
quote:
Originally posted by mcerd1
I hope your all sitting down for this - but I've actually found some time to work on my car
I figured it was about time to finish building the engine and one of the first jobs on the list was to check the valve to piston clearance
So I finished off the head, set the valve clearances, stuck it on with some plasticine on the pistons (using a spare gasket and belt)
then timed the cam with my dial gauge (which was nearly 8° off using the nearest tooth on the belt!) and turned it over a few times by hand, stripped
the head back off and measured the plasticine at a min of 2mm clear
its only at this point that I realised I don't know what the minimum acceptable clearance should be for these engines and despite searching for
some time now I can't find any conclusive answers
the figures I've see range from just over 1mm (0.040" ) to more than 2.5mm - and some just say as much as possible.....
Any thoughts ?
I have 2.0 fuel injection head skimmed by 1.5mm and have been running with a valve to piston clearance of 1.5mm for years, don't know if it
would be a problem on a track car though.
|
|
|
Mr Whippy
|
| posted on 15/7/16 at 07:13 PM |
|
|
I'm more interested in how this clearance can reduce while running?
Assuming the valve springs are strong enough, are we talking metal expansion or valve float reducing the clearance. I'd have thought the engine
block would expand more than the piston or rod given it's greater length so maybe the clearance would actually increase?
[Edited on 15/7/16 by Mr Whippy]
|
|
|
Ian.C
|
| posted on 15/7/16 at 07:57 PM |
|
|
All I can say is that my engine gets abused, its still good after 5 years. Maybe your over thinking the situation.
|
|
|
snapper
|
| posted on 16/7/16 at 04:50 AM |
|
|
Piston to deck clearance is quoted as 0.9mm safe 0.75 race this is to account for rod stretch at high revs
Therefore 2mm is more than enough
If you change camshaft for 1 with more lift you should check again
Full lift is after TDC so chasing the piston down the bore and it won't catch it
Lift at TDC is the place you need to worry about and you can increase the gap by retarding the cam timing
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
Nickp
|
| posted on 16/7/16 at 10:22 AM |
|
|
I'd say 2mm will be fine too, presuming valve springs are up to the job.
|
|
|
mcerd1
|
| posted on 16/7/16 at 03:07 PM |
|
|
quote:
Originally posted by Mr Whippy
I'm more interested in how this clearance can reduce while running?
Assuming the valve springs are strong enough, are we talking metal expansion or valve float reducing the clearance. I'd have thought the engine
block would expand more than the piston or rod given it's greater length so maybe the clearance would actually increase?
I believe the 2 biggest issues are rod stretch at high RPM and expansion of the exhaust valves
obviously made worse by the longer duration and higher lift cam (mine is a piper 285 which is meant to be 270° inlet and 290° exhaust with 11.81mm
lift)
quote:
Originally posted by Nickp
I'd say 2mm will be fine too, presuming valve springs are up to the job.
the spring are new and supplied with the cam - but I have to admit I never checked the spring rates...
[Edited on 16/7/2016 by mcerd1]
-
|
|
|
IanSouthLincs
|
| posted on 16/7/16 at 10:44 PM |
|
|
According to the guide Burtons give out they specify 1.5mm or 60 thou minimum clearance, so you're well within tolerance. I used a Piper 285
with a Victor Reinz 1.3mm gasket and 40 thou head skim and got 1.8mm clearance when I did the plasticine test. Hope this helps 👍
|
|
|
mcerd1
|
| posted on 18/7/16 at 01:00 PM |
|
|
cheers guys, it gives me a bit more confidence 
next up - I'd better check the actual combustion chamber volumes and spark plug tip clearance too.....
-
|
|
|
