Piston up = valves down?

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Model T Ford Forum: Forum 2017: Piston up = valves down?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ignacio Valdes on Tuesday, March 07, 2017 - 10:17 am:

If a piston is at the top position are the valves supposed to be all the way down?


Top of pagePrevious messageNext messageBottom of page Link to this message  By G.R.Cheshire on Tuesday, March 07, 2017 - 10:21 am:

Depends weather you are on the compression or the exhaust stroke. If you are on the exhaust stroke the exhaust valve will be open and as the piston starts down the intake valve will open then when you come up on the compression stroke the intake should close


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Tuesday, March 07, 2017 - 10:28 am:

Yes and no. When a piston is "at the top" or TDC it is either at the end of the compression stroke and for sure both valves are supposed to be closed and they have been for approximately 180 degrees of crankshaft rotation.

The only other possibility is that the piston is at the end of the exhaust stroke. At that point, In most engines the exhaust valve is almost closed and the intake valve is just beginning to open. This is sometimes referred to as split overlap. I'm not sure if stock T valve timing has that or not.

This period of valve overlap is intended to get the intake charge started sooner for more thorough filling of the cylinder and in turn more power. The rough idle of many high performance engines is due to cam grinds which use a lot of overlap at that point. That makes for better cylinder filling at higher rpm at the expense of poor idle quality.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ignacio Valdes on Tuesday, March 07, 2017 - 11:31 am:

The valve circled in red seems to not close completely?

Loose valve?


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Tuesday, March 07, 2017 - 12:19 pm:

That's because the one next to is closed all the way, so the one you circled is at the end of the exhaust stroke. Turn the crankshaft around one turn and the other one will look like that and the one you circled will be closed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Tuesday, March 07, 2017 - 12:22 pm:

What does it look like after turning the engine one (And only one) complete revolution? In the position shown, one of the two center cylinders should have both valves COMPLETELY closed. The other of the two center cylinders should have both valves SLIGHTLY open. If you were to then turn the crankshaft one complete revolution, the one that had two closed valves would now have two slightly open valves and vice versa.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Tuesday, March 07, 2017 - 12:23 pm:

Oops, David and I were typing at the same time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Blake, Kansas City on Tuesday, March 07, 2017 - 01:21 pm:

Ignacio,

The one you have circled is the #3 intake valve. Are you saying it never closes completely? With the #3 piston in that position you are either at the end of the exhaust stroke and about to start the intake stroke, or you are at the top of the compression stroke. If the latter, both valves should definitely be closed. If at the top of the exhaust stroke the intake valve could be just starting to open. Have you checked the clearance of that valve?


Top of pagePrevious messageNext messageBottom of page Link to this message  By James Baker on Tuesday, March 07, 2017 - 01:30 pm:

Ignacio,

Google "how does a 4 stroke engine work". Should help you and solve some questions you have.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Matthiesen on Tuesday, March 07, 2017 - 03:46 pm:

Ignacio, In your picture the #4 intake valve is also open. If that valve spring is for the #4 exhaust valve that is out of engine and #4 intake still has its spring, then some thing is wrong because #4 is at BDC and the intake valve should be closed. Or did you circle the wrong valve in question in red ? As I remember this engine never did run correctly for you. Maybe something is wrong with the cam gear timing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Tuesday, March 07, 2017 - 04:02 pm:

Well, gee Kevin, there's NO exhaust valve in #4, that could cause a problem!! :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Eubanks, Powell, TN on Tuesday, March 07, 2017 - 05:23 pm:

It will only be a matter of time before you have a problem with those original valves, The heads pop off!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Duey_C on Wednesday, March 08, 2017 - 01:10 am:

Ignacio, if you are having trouble with this part, PM me. I'll help. I'm damn slow to respond but I will help.
Caution. I'm a junkyard style mechanic with my 2 clunkers (my '24 Crappy Lizzhe and Lucky the TT). Heh. I typed "junktard". Some of you prob'ly think that of me too. That's OK. :-) If I'm way off base just ignore this post.
My 2 clunkers and my '18 Tin Cup run like they should.
If you are having problems getting that valve all the way down so you can lap it against the seat; yeah your valve stem prob'ly needs some clearance.
Is that where this comes from? If not, please ignore all of this babbling!
As you lap a valve, grind a valve, clean up a seat or otherwise take material away from the seat or the head of a valve, the stem below gets "longer" and must be shortened the same amount.

Take each one of the cylinders during your valve lapping, find the true top dead center for each of them where the piston WAS coming UP with the exhaust valve closed for that cylinder (the compression stroke) and stop the piston at the top. You are there. 1243. Now check the valve stem clearance as you lap the valves in that cylinder. Each valve in each cylinder.
Get those springs and washers out of there and set them aside for this please.
Is the bottom of the valve stem touching the valve lifter that raises and lowers that valve and stem? If so take the valve to the bench grinder and remove a very small amount, rotating the valve stem in your fingers while keeping it as straight as possible to the grinder's stone and try it again in the engine.
Just to get it running, forget about cupping of the lifters for right now. You'll replace those valves and hopefully the lifters anyway. Soonish please? So the valves don't come apart.
If about 3 or 4 pieces of printer paper (about .012") would fit between the bottom of the valve stem and the lifter, you're close. Move to the next valve then move the next cylinder into position.
This is wrong but it works. I did this on my TT last fall just to get it running. I ground some valves, cleaned up the seats and used the bench grinder to give the stem clearance since my valve grinders don't have that handy accessory.
If doing it right? Do it right. :-)
Junktard's mechanicking done.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Wednesday, March 08, 2017 - 01:59 am:

I have ground valve stems for years with a piece of angle iron clamped next to the grinder so I can hold the stem in the V and turn it to get an even grind on the end of the stem. I actually set it up at about a 45 degree angle so I grind a cup into the stem. As I get close to the correct clearance, I switch to grinding it on the side for a flat finish--if I've done that right, it leaves a very small dimple in the valve stem end to hold a drop of oil to cushion the closure when the lifter hits the stem.
I know, anal retentive!--But it's worked for me!!
:-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Matthiesen on Wednesday, March 08, 2017 - 02:29 am:

David, It says #4 INTAKE valve is open at BDC.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Matthiesen on Wednesday, March 08, 2017 - 02:57 am:

Ignacio, Follow Duey's instructions and David's regarding valve stem grinding back yard style. In using the needle nose pliers as you show the your other post to lap valves you most likely won't need much valve stem grinding.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bain Loo on Thursday, March 09, 2017 - 08:43 am:

in compression stroke yes both valves will be closed. it looks almost normal seems like 1st cylinder in inlet stroke and last one in the beginning of exhaust.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Thursday, March 09, 2017 - 05:34 pm:

Kevin, Yes, I read that, but no one had mentioned that #4 Exhaust is missing! :-)
Pilot complaint: Left engine missing
Response: Found Left engine on wing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Matthiesen on Thursday, March 09, 2017 - 07:30 pm:

David, I have seen that full list of UPS pilot complaints and mechanic responses, it is really funny but to long to list here.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Thursday, March 09, 2017 - 07:46 pm:

Kevin,
True! But I thought that one short enough to post here--and not too "Plane" for this crowd!
A pun is a terrible thing to waist. . . . Just look at my waist! :-)
One of my favorites:
Pilot: Auto-land rough.
Reply: Auto-land not installed on this plane.


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