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Topic Review (Newest First)
12-11-2018 03:04 PM
ericnova72
Quote:
Originally Posted by Molon Labe View Post
Thanks, I think I'm going check with the dial indicator and use the clay as well. I'd like to gain the experience.
Certainly, no fault in doing that
12-11-2018 08:21 AM
Molon Labe Thanks, I think I'm going check with the dial indicator and use the clay as well. I'd like to gain the experience.
12-11-2018 07:40 AM
alwill923 I think we are making this way to complicated. First degree cam and check TDC. Put helper springs on the valves, install rocker arms, push rods and adjust valve clearance with lifter on cam's base circle as one would normally do. With hydraulic lifters adjust to zero lash only. The spring in the hydraulic lifter should be strong enough to compress the helper spring without collapsing the lifter. With solids adjust for clearance. Bring crank to 20 degrees before TDC. Put dial indicator on the valves spring retainer perpendicular to the valve stem. Zero dial indicator. Push valve (either one) lightly until it hits the piston. Now rotate the engine keeping light pressure on the valve to make contact with the piston until the dial indicator reads the smallest number and starts to increase. The smallest number is the valve clearance. Check by letting valve up and check to see if dial indicator goes to zero (valve is seated). Do the other valve. should take no more than a few minutes. Make sure to always turn the crank in the direction of rotation. Of course this does not check the clearance in the valve pocket, only clay can do this.
12-10-2018 06:41 PM
techinspector1 I learned what I know from many different sources, and somewhere along the way I was taught to check intake and exhaust with a dial indicator at -20, -15, -10, -5, ZERO, +5, +10, +15, +20 on both intake and exhaust. Have I ever been that meticulous......No.
12-10-2018 06:15 PM
Molon Labe Thank you. Good information.
12-10-2018 04:18 PM
ericnova72 Valve fully open and piston at TDC will not clear even a stock .390" lift cam....you have to do it with the timing chain installed and degree'd correctly.

Closest the intake valve will come to the piston is just slightly past TDC, the intake valve is opening faster than the piston is starting to move away from it.....that's why the 5 to 15 before and after TDC measuring points.
12-10-2018 03:44 PM
Molon Labe Eric,

I agree with everything you said but perhaps I didn't explain myself completely. Under any circumstances, the closest the valve can possibly come to the piston is when the piston is at TDC and the valves are fully opened. In the scenario I offered I should have added that with the piston at TDC and no timing chain you can carefully rotate the cam by hand to achieve max lift for intake. Then, assuming there's no interference, measure the clearance with a dial indicator on the valve stem. Then repeat for exhaust. Am I missing something?
12-10-2018 02:38 PM
ericnova72
Quote:
Originally Posted by Molon Labe View Post
I think if you installed the cam and crank without the timing chain, set the cam so that both valves were completely closed. Then brought the #1 to TDC and measured the piston/valve clearance with the method Fang pointed out it would be the absolute worst condition. If you have adequate clearance there you're assured you'll be ok anywhere before or after TDC.
NOPE....not when you've got the intake valve opening before TDC and the exhaust valve closing after TDC.....the overlap period when both valves are slightly open, the intake is opening and the exhaust is closing at the same time.
This fact is how long tube headers help draw in more intake mixture at the time the piston is at TDC and hasn't yet started moving down the bore with enough velocity to draw on the intake port itself. The leaving exhaust pulls a vacuum pulse on the header tube and exhaust port, with both valves slightly open at overlap it starts to pull air/fuel mix into the chamber from the slightly open intake valve.

That's why the instruction with the indicator method is to check P-to-V clearance on the intake valve between 15 Before TDC and 5 Before TDC as the closest point between valve and piston is generally going to fall into that range with most performance cams....only very mild to dead stock cams will have the closest point less that 5 Before on the intake valve. Same with the exhaust valve, closest point is going to be just before piston reaches TDC as this is the point the exhaust is still the furthest open as the piston is coming to TDC Overlap.
12-10-2018 07:54 AM
AutoGear If you use clay for mocking/checking things, it NEEDS to be oil-based modeling clay (sometimes called plastilina/plastelina), not play-doh type stuff
12-10-2018 06:33 AM
Molon Labe I think if you installed the cam and crank without the timing chain, set the cam so that both valves were completely closed. Then brought the #1 to TDC and measured the piston/valve clearance with the method Fang pointed out it would be the absolute worst condition. If you have adequate clearance there you're assured you'll be ok anywhere before or after TDC.
12-09-2018 06:58 AM
alwill923 https://www.hotrod.com/articles/dyno...plane-intakes/
12-08-2018 05:00 PM
techinspector1
Quote:
Originally Posted by Molon Labe View Post
Tech, you mentioned a modest cam with no more than 240-250 intake duration. Is that at .050”?
Yes.

Quote:
Originally Posted by Molon Labe View Post
I did the math for the fun of it (retired engineer). At 5 before or after TDC the piston is just under .009” below TDC, at 10 it’s about .035” and at 15 it’s .077” below.
The wild cards are that the cam can be phased advanced or retarded relative to the piston position in the bore, the other variable is piston deck height.
12-08-2018 03:35 PM
Molon Labe Thanks yet again guys. Fang, that was an interesting article and an informative website as well. I’m going to go through that exercise just for the experience as well as the information I’ll gain. Although, after hearing that Eric had no issues with the engine he describes I doubt I’ll have any issues. I don’t plan to have anywhere near the lift or duration he did. Tech, you mentioned a modest cam with no more than 240-250 intake duration. Is that at .050”?

I did the math for the fun of it (retired engineer). At 5 before or after TDC the piston is just under .009” below TDC, at 10 it’s about .035” and at 15 it’s .077” below.
12-08-2018 11:56 AM
ericnova72
Quote:
Originally Posted by Fang16 View Post
Found this at https://www.enginelabs.com/engine-te...lve-clearance/
Is it a good way to do it?


For the dial indicator method, follow all the previous setup steps except placing clay on the piston top. Again, use solid lifters, install the rocker arms and set zero lash. Rotate the crankshaft clockwise until the degree wheel indicates the Number 1 piston is at 10 degrees ATDC on the intake stroke. This is the crank angle where interference is most likely to happen--not at TDC or at maximum intake-valve lift. At this point, the piston on its way down and, depending on the cam lobe profile, the intake valve is trying to chase it down. Mount the dial indicator on the cylinder head and position it over the retainer of Number 1 intake valve. Set the dial indicator to zero. Make sure that the plunger on the dial indicator has plenty of range to move up and down. Use a small screwdriver or pick to push tip of the rocker arm downward until you feel the valve contact the piston. Observe the dial indicator to determine the actual piston to valve clearance. To measure the clearance on the exhaust valve, rotate the motor clockwise until the timing wheel is at 10 degrees BTDC on the exhaust stroke. Again, this is the crankshaft position most likely to see P2V interference as the piston moves up and draws a bead
This does work, but I'll add a little info about it...

You'll want to check every 2 from 5-15 to find the point the piston and valve are the closest, as 10 is not going to be right in a lot of cases, so best to sneak up on it and locate the closest contact point for your build and go with that for the reference.

This method will tell you if the piston relief is deep enough....but it won't tell you radial clearance(whether the eyebrow relief is big enough in diameter to clear the valve diameter.....clay is still about the only way you can get that measurement.
12-08-2018 07:49 AM
Fang16 Found this at https://www.enginelabs.com/engine-te...lve-clearance/
Is it a good way to do it?


For the dial indicator method, follow all the previous setup steps except placing clay on the piston top. Again, use solid lifters, install the rocker arms and set zero lash. Rotate the crankshaft clockwise until the degree wheel indicates the Number 1 piston is at 10 degrees ATDC on the intake stroke. This is the crank angle where interference is most likely to happen--not at TDC or at maximum intake-valve lift. At this point, the piston on its way down and, depending on the cam lobe profile, the intake valve is trying to chase it down. Mount the dial indicator on the cylinder head and position it over the retainer of Number 1 intake valve. Set the dial indicator to zero. Make sure that the plunger on the dial indicator has plenty of range to move up and down. Use a small screwdriver or pick to push tip of the rocker arm downward until you feel the valve contact the piston. Observe the dial indicator to determine the actual piston to valve clearance. To measure the clearance on the exhaust valve, rotate the motor clockwise until the timing wheel is at 10 degrees BTDC on the exhaust stroke. Again, this is the crankshaft position most likely to see P2V interference as the piston moves up and draws a bead
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