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hemi piston to head clearance specs or minimum.... #1657369 08/11/14 05:34 AM 08/11/14 05:34 AM
Joined: Oct 2003 Posts: 1,794 BC Canada O ogopogo OP top fuel
ogopogo OP top fuel O Joined: Oct 2003 Posts: 1,794 BC Canada	i was checking my piston to valve clearance today with clay and noticed my piston to head clearance is rather tight on the piston dome sides(front and back of the piston looking at the motor from the front).i busted out my ancient direct connection engine manual and I am well under the spec in the book but times have changed so to speak so wondering if you guys check this and what is a safe minimum.I am running the best composition gasket which is 050 thickness

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657370 08/11/14 10:37 AM 08/11/14 10:37 AM
Joined: Jan 2007 Posts: 4 Mission BC Canada J Jim I member
Jim I member J Joined: Jan 2007 Posts: 4 Mission BC Canada	.058 to .060 minimum clearance. check it with a dial indicator thru the spark plug hole.

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657371 08/11/14 02:25 PM 08/11/14 02:25 PM
Joined: Aug 2003 Posts: 43,157 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,157 Bend,OR USA	Quote: i was checking my piston to valve clearance today with clay and noticed my piston to head clearance is rather tight on the piston dome sides(front and back of the piston looking at the motor from the front).i busted out my ancient direct connection engine manual and I am well under the spec in the book but times have changed so to speak so wondering if you guys check this and what is a safe minimum.I am running the best composition gasket which is 050 thickness It depends on which rod and head material and intended RPM I would shoot for .035 to .040 on a steel rod motor kept under 7000 RPM with iron heads, add .005 up to 8500 RPM and shoot for .055 to .070 on a aluminum rod motor with the same RPM Aluminum heads need more also Keep in mind that to much P.TO V and P to the head is a lot safer than a tiny bit to little Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: hemi piston to head clearance specs or minimum.... [Re: Cab_Burge] #1657372 08/11/14 02:39 PM 08/11/14 02:39 PM
Joined: Oct 2003 Posts: 1,794 BC Canada O ogopogo OP top fuel
ogopogo OP top fuel O Joined: Oct 2003 Posts: 1,794 BC Canada	Ok,so ive got about 035 clearance and it is a steel rod,iron head under 7k rpm motor,4 speed trans.....

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657373 08/11/14 03:10 PM 08/11/14 03:10 PM
Joined: Oct 2003 Posts: 1,794 BC Canada O ogopogo OP top fuel
ogopogo OP top fuel O Joined: Oct 2003 Posts: 1,794 BC Canada	old larry shepard direct connection racing manual states 055 minimum and pistons will hit the head at 045.......

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657374 08/11/14 03:52 PM 08/11/14 03:52 PM
Joined: Apr 2005 Posts: 1,505 TN S SCATPACK 1 pro stock
SCATPACK 1 pro stock S Joined: Apr 2005 Posts: 1,505 TN	Follow what Cab said and shoot for 35 to 40 thousands piston to head clearance. The old manuals were for a different metal in the pistons that expanded more. If yo were using aluminum rods, I would recommend more clearance. But that should give you good quench (if there is such a thing on a HEMI). Old Geezer Racing

Re: hemi piston to head clearance specs or minimum.... [Re: Jim I] #1657375 08/11/14 03:57 PM 08/11/14 03:57 PM
Joined: Apr 2005 Posts: 1,505 TN S SCATPACK 1 pro stock
SCATPACK 1 pro stock S Joined: Apr 2005 Posts: 1,505 TN	Quote: .058 to .060 minimum clearance. check it with a dial indicator thru the spark plug hole. You can't check a Hemi for dome to head clearance through the spark plug hole with a dial indicator. That will only tell you how much clearance you have for the spark plug. Only way I know, for the average person, to check the dome to head clearance is using clay. Some shops may have some of the lazer measuring tools that could measure the dome and compare it to the curved head surface, but the average person does not have this equipment. Old Geezer Racing

Re: hemi piston to head clearance specs or minimum.... [Re: SCATPACK 1] #1657376 08/11/14 04:17 PM 08/11/14 04:17 PM
Joined: Jan 2012 Posts: 2,645 Stuttgart, Arkansas rickseeman master
rickseeman master Joined: Jan 2012 Posts: 2,645 Stuttgart, Arkansas	Quote: You can't check a Hemi for dome to head clearance through the spark plug hole with a dial indicator. I would disagree with that. Seems like the easiest way to me. Mock engine up, piston at TDC, place dial indicator in spark plug hole, zero indicator, remove rod bolts, push up rod until piston hits head, read distance on indicator. P.S. Don't use too much clay checking valve to piston clearance. Don't ask me how I know. Last edited by rickseeman; 08/11/14 04:18 PM. 2011 Drag Pak Challenger

Re: hemi piston to head clearance specs or minimum.... [Re: rickseeman] #1657377 08/11/14 05:28 PM 08/11/14 05:28 PM
Joined: Jul 2009 Posts: 413 Norway (old world) Oyvind Mopar mopar
Oyvind Mopar mopar Joined: Jul 2009 Posts: 413 Norway (old world)	Please be careful with the Hemi piston dome clearance! The clearance on the dome sides need to be bigger, as proposed by OP because the pistons also expand sideways from the heat. And they do expand a lot, for comparison you can see the radial clearance that all pistons have above the top ring, (I just measured a 4" hyper that is .050" smaller above top ring than down skirt). The Hemi dome will expand sideways and up due to heat, so it needs more clearance due to the dome. When I used my old TRW hitop pistons in the late '70's there was a small sticker inside each box that warned about minimum vertical clearance of .060" (I think it was .060 or .065), which was supposed to take care of this expansion as well as rod stretch etc. My

Re: hemi piston to head clearance specs or minimum.... [Re: rickseeman] #1657378 08/11/14 05:33 PM 08/11/14 05:33 PM
Joined: Mar 2006 Posts: 9,910 Eighty Four, PA B G Racing master
B G Racing master Joined: Mar 2006 Posts: 9,910 Eighty Four, PA	Check the clearence at the compression height at the edge of the piston and try to achive .055 and put peanut size balls of clay on both sides of the dome.You want minimum of .055 at all areas,we like a little more at the dome areas depending on rods,CR and piston clearence. [IMG]http://i430.photobucket.com/albums/qq21/ajcasini/max_zpsdppwd9km.jpg[/IMG]

Re: hemi piston to head clearance specs or minimum.... [Re: rickseeman] #1657379 08/11/14 06:32 PM 08/11/14 06:32 PM
Joined: Apr 2005 Posts: 1,505 TN S SCATPACK 1 pro stock
SCATPACK 1 pro stock S Joined: Apr 2005 Posts: 1,505 TN	Quote: Quote: You can't check a Hemi for dome to head clearance through the spark plug hole with a dial indicator. I would disagree with that. Seems like the easiest way to me. Mock engine up, piston at TDC, place dial indicator in spark plug hole, zero indicator, remove rod bolts, push up rod until piston hits head, read distance on indicator. Rick, Well duh on my part. I am going to chalk it up to "my sometimers" memory. I knew that... Not sure what I was thinking earlier, so disregard my first post. Old Geezer Racing

Re: hemi piston to head clearance specs or minimum.... [Re: SCATPACK 1] #1657380 08/11/14 07:23 PM 08/11/14 07:23 PM
Joined: Oct 2003 Posts: 1,794 BC Canada O ogopogo OP top fuel
ogopogo OP top fuel O Joined: Oct 2003 Posts: 1,794 BC Canada	Im going to have to source a thicker head gasket,I only have as little as 035 on the sides of the dome,just rechecked cyl 1 and 6 with two different heads I have and both are too tight.I put 6 little balls of clay on each piston ...Seems my deck height is lower than I expected and just called shop that did all the block machining and found out they machined everything but didn't check deck height ???.

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657381 08/11/14 07:46 PM 08/11/14 07:46 PM
Joined: Aug 2003 Posts: 43,157 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,157 Bend,OR USA	Quote: Im going to have to source a thicker head gasket,I only have as little as 035 on the sides of the dome,just rechecked cyl 1 and 6 with two different heads I have and both are too tight.I put 6 little balls of clay on each piston ...Seems my deck height is lower than I expected and just called shop that did all the block machining and found out they machined everything but didn't check deck height ???. Hemiroid motors, ain't they fun Them motors have a lot more issues than some of the other motors have But you can fix it Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: hemi piston to head clearance specs or minimum.... [Re: Jim I] #1657382 08/11/14 10:16 PM 08/11/14 10:16 PM
Joined: Aug 2003 Posts: 1,313 Charlotte, NC L LSP pro stock
LSP pro stock L Joined: Aug 2003 Posts: 1,313 Charlotte, NC	Quote: .058 to .060 minimum clearance. check it with a dial indicator thru the spark plug hole. This is correct, the clearance needs to be measured vertically, the Super Stock Hemi builders do it this way. While .055" radial clearance is more than is required and will undoubtedly 100% keep the piston from ever hitting the head in that plane, performance will not be optimum.

Re: hemi piston to head clearance specs or minimum.... [Re: LSP] #1657383 08/11/14 10:56 PM 08/11/14 10:56 PM
Joined: Mar 2006 Posts: 9,910 Eighty Four, PA B G Racing master
B G Racing master Joined: Mar 2006 Posts: 9,910 Eighty Four, PA	Quote: Quote: .058 to .060 minimum clearance. check it with a dial indicator thru the spark plug hole. This is correct, the clearance needs to be measured vertically, the Super Stock Hemi builders do it this way. While .055" radial clearance is more than is required and will undoubtedly 100% keep the piston from ever hitting the head in that plane, performance will not be optimum. Measuring with the indicator will give you the precise clearence of any part of the piston that is closest to the head.For most engines used for street and bracket racing a little extra clearence is good insurance against a catastrophic hic-cup.On any scienced out class race type engine the tighter the better.We used to get the dome as close as possible untill we saw shiney areas on the dome,but no contact marks.This was great for making power but put the engine close to "kill"with the slightest screw up.This can be quite costly.If you want a fast engine by all means tighten it up,if you want a dependable engine that will give you good performance and longitivity give it some extra. [IMG]http://i430.photobucket.com/albums/qq21/ajcasini/max_zpsdppwd9km.jpg[/IMG]

Re: hemi piston to head clearance specs or minimum.... [Re: B G Racing] #1657384 08/11/14 11:10 PM 08/11/14 11:10 PM
Joined: Jan 2003 Posts: 6,392 nielsville, minn. Q quickd100 master
quickd100 master Q Joined: Jan 2003 Posts: 6,392 nielsville, minn.	I had my 528 set at zero deck with a .042 head gasket and thought I was safe. I was pretty new to dyno operation at the time. I had too small restrictors on the exhaust side of the dyno on a couple pulls. Well the motor went to 8000 and the pistons kissed the heads. I run .052 gaskets now. Dave

Re: hemi piston to head clearance specs or minimum.... [Re: ogopogo] #1657385 08/11/14 11:20 PM 08/11/14 11:20 PM
Joined: Aug 2003 Posts: 270 M MIKECS enthusiast
MIKECS enthusiast M Joined: Aug 2003 Posts: 270	The answer is to use a piece of solder tape it across the piston. Turn the motor over measure the dome and sides of the compressed solder. Put the head back on put a few bolts tighten down. You should be around .055 to .062 any more you will loose quench and less you could touch the head. Any questions call me at 630-923-2897 8237282-Picture002.jpg (327 downloads)

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