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Re: Help checking piston to valve clearance??
[Re: 451Mopar]
#851591
11/13/10 01:38 AM
11/13/10 01:38 AM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
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master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
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Quote:
It is difficult to estimate the Piston/valve clearance on paper unless you know the true cam lobe profile (duration at multiple lobe lift points), lobe seperation angle, and installed center-line.
The cams maximum lift does not mean much because the piston will have moved down in the cylinder quite a bit by then. Other information needed for an estimate would be the closed valve position to piston clearance at TDC, and the stroke/rod length to figure the piston movement around TDC.
Like I said, using math to estimate (model) the PV clearance is not easy.
The easy solution is checking with the actual cam installed. Both intake and exhaust will need to be checked. First you need to install your checking springs, a solid tappet (or tappet that won't compress under the checking spring load), and set the lash. Setting zero lash is best, you can add in lash to the PV numbers later.
With the dial indicator setup on the valve retainer, you just push the valve down till it contacts the piston and take the PV reading directly, but you have to do this at several crank positions because the least clearance point is unknown.
Usually the PV is tightest around 10-20 degrees Before (exhaust) and after (intake) TDC depending on the above mentioned cam parameters, including the cams installed position.
I agree, Jim. A situation like this is another reason I'd like to see cams sold with graphs instead of just the .050" number. So regardless of the piston profile dead accurate measurements could still be made.
Last edited by 64Post; 11/13/10 01:40 AM.
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Re: Help checking piston to valve clearance??
[Re: RapidRobert]
#851594
11/13/10 08:34 AM
11/13/10 08:34 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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i always thought the sure fire way was to put clay on the piston, mock everything up and run it through a full sweep, then take it apart and measure the clay. if you feel contact/resistanct, then stop.
**Photobucket sucks**
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Re: Help checking piston to valve clearance??
[Re: Junky]
#851595
11/13/10 11:02 AM
11/13/10 11:02 AM
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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Quote:
383 engine with the heads on, engine in the car. Heads are the 346 kind.
The clay method works great because you can see where the valves match up with the reliefs in the piston, but you have to remove the cylinder head. The method I described works without removing the head.
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Re: Help checking piston to valve clearance??
[Re: RapidRobert]
#851596
11/13/10 01:50 PM
11/13/10 01:50 PM
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Joined: Jan 2003
Posts: 5,186
Wherever I am.
Junky
OP
master
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OP
master
Joined: Jan 2003
Posts: 5,186
Wherever I am.
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Quote:
Quote:
Cam is 10 degrees retarded.
That cant be right
That does seem like a lot. We're going to go over it again Sunday.
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Re: Help checking piston to valve clearance?? UPDATE
[Re: rss]
#851599
11/17/10 12:56 PM
11/17/10 12:56 PM
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Joined: Jan 2003
Posts: 5,186
Wherever I am.
Junky
OP
master
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OP
master
Joined: Jan 2003
Posts: 5,186
Wherever I am.
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Quote:
 What's the verdict? Are you happy with the cam swap?
I haven't had time to tune the engine. It sounds really healthy and winds to 6k with ease. It pulls hard. The tune on it now is more for the old cam. I need to work the distributor and carb over. Once I get it tuned up I'll post back the results.
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Only one cymbal on the crank timing gear key way which is a V, nothing on the other two key ways. And I didn't have any keys for the cam timing gear. Can't finish up until Sunday.
