New motor, will my valves hit my pistons?
Newbie
Joined: Feb 2017
Posts: 8
Likes: 0
From: Puerto Rico
The clay method is straightforward, reliable, and easy if the engine is on a stand. One simply rotates the piston around TDC on the intake stroke and checks the depth of the clay at the thinnest areas for both intake and exhaust valve impressions, just like using a tire tread depth gauge.
When the engine is at operating temperature, clearances change. This is why one should observe a minimum of 0.060" for the intake and 0.100" for the exhaust to account for thermal expansion. If there is an issue, one can either (a) change the cam timing and be content with that, or (b) gently massage the reliefs with a Dremel to attain the desired clearance. The latter option is always preferable. As for using a thicker head gasket, that may be an option in some cases, but one should never expand the quench area between the piston perphery and head surface to >0.060". This is important.
In my case, the reliefs in the aftermarket pistons were insufficient to account for the larger valves, advanced intake LC, 12mm lift and rapid ramp rates. It was just as well, as we used this opportunity to gently radius all sharp edges on the piston crowns, which is helpful in thwarting preignition.
When the engine is at operating temperature, clearances change. This is why one should observe a minimum of 0.060" for the intake and 0.100" for the exhaust to account for thermal expansion. If there is an issue, one can either (a) change the cam timing and be content with that, or (b) gently massage the reliefs with a Dremel to attain the desired clearance. The latter option is always preferable. As for using a thicker head gasket, that may be an option in some cases, but one should never expand the quench area between the piston perphery and head surface to >0.060". This is important.
In my case, the reliefs in the aftermarket pistons were insufficient to account for the larger valves, advanced intake LC, 12mm lift and rapid ramp rates. It was just as well, as we used this opportunity to gently radius all sharp edges on the piston crowns, which is helpful in thwarting preignition.
do i need to mill some off the piston for moore clearance or leave it as is?
I don't know anything about your valves (+1? +2?), cams, cam timing, valvesprings, etc., but all these things factor into the picture.
There's no way I'd run a valve with only 0.010" clearance from the piston as-is.
There's no way I'd run a valve with only 0.010" clearance from the piston as-is.
Newbie
Joined: Feb 2017
Posts: 8
Likes: 0
From: Puerto Rico
You'll need to identify the source of the problem, because normally that setup shouldn't pose a problem. Things that will aggravate valve/piston clearance are a shaved head, valve job, advanced intake cam, etc.
Newbie
Joined: Feb 2017
Posts: 8
Likes: 0
From: Puerto Rico
Will take this opportunity to pose a question to Ted.
I have .5 over valves, supertech dual springs, Ti retainers. Short block is OEM, and will use OEM MLS Head gasket. Presently running a comp 272.
I want to change cams for Kelford 272s. Do you suspect any issues? Any opinion on switching from comp to kelford 272?
I have .5 over valves, supertech dual springs, Ti retainers. Short block is OEM, and will use OEM MLS Head gasket. Presently running a comp 272.
I want to change cams for Kelford 272s. Do you suspect any issues? Any opinion on switching from comp to kelford 272?
I'm currently wondering how to check this on a mivec motor, especially the intake cam. I want to grind the nub to get more advanced back (2.4) but I don't want to over do it. I would have to figure out how to roll the motor by the cam?
Evolved Member
Joined: Mar 2008
Posts: 2,110
Likes: 320
From: Croatia
a bit of a expensive solution is to get an manually adjustable pulley and use it on the intake cam instead of the mivec pulley... I need to check if that works though.. have to drop by the workshop and see.. this would allow you to check the valve clearence even in the fully advanced position..
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