Finding Top Dead Center 239 V8 Flathead
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Joined: Feb 2003
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From: LOS ANGELES
Finding Top Dead Center 239 V8 Flathead
This is my first post and even tho I have a tiny bit of knowledge now on finding TDC I would like to know if there is an easy way to find TDC on my engine that sits on a stand with the heads, gear cover, and pulley already installed. I have not installed the intake or pan.
I performed this last night:
The small bump on the pulley is lined up with the pin on the gear cover, both #1 exhaust and #2 intake valves are down and have a slight gap at the bottom where the lifters are. I turned the crank slowly clock wise and after a bit the #1 valve begins to travel up and as i keep turning and the bump is making its full orbit the #1 begins to go back down and then the #2 valve begins to travel up and when the bump reaches its full 2nd orbit both valves are down and both have have the same gap once again.
So after 2 full turns they end up where they started.
I hope this is what is supposed to happen
I performed this last night:
The small bump on the pulley is lined up with the pin on the gear cover, both #1 exhaust and #2 intake valves are down and have a slight gap at the bottom where the lifters are. I turned the crank slowly clock wise and after a bit the #1 valve begins to travel up and as i keep turning and the bump is making its full orbit the #1 begins to go back down and then the #2 valve begins to travel up and when the bump reaches its full 2nd orbit both valves are down and both have have the same gap once again.
So after 2 full turns they end up where they started.
I hope this is what is supposed to happen
Postmaster
Joined: Mar 2000
Posts: 3,730
Likes: 13
From: Waynesville, OH
Welcome aboard, Moses! 
I see you have been away for a couple of years. Well, there are some of the old characters still on the forum and a whole new cast for you to meet.
As far as the timing goes, that's what is supposed to happen. As you turn the engine over, the intake valve will close and you should have a full crank revolution (approximately) before the exhaust valve starts to open. TDC on the firing stroke is at the middle of this crank revolution, with the piston at the top of its travel.
As far as the exact timing chain markings and chain/tooth alignment, one of the flathead gurus will be along to confirm your bump and pin settings.
I see you have been away for a couple of years. Well, there are some of the old characters still on the forum and a whole new cast for you to meet. As far as the timing goes, that's what is supposed to happen. As you turn the engine over, the intake valve will close and you should have a full crank revolution (approximately) before the exhaust valve starts to open. TDC on the firing stroke is at the middle of this crank revolution, with the piston at the top of its travel.
As far as the exact timing chain markings and chain/tooth alignment, one of the flathead gurus will be along to confirm your bump and pin settings.
Cross-Country
Joined: Jan 2005
Posts: 76
Likes: 2
From: Donnellson, IA
The bump and pin are actually 4 degrees advance(distributor initial advance). Use these for setup. As far as TDC, use the old method of covering the spark plug hole to find the compression stroke then wire up the plugs from there.
Lead Driver
Joined: Oct 1999
Posts: 6,776
Likes: 553
From: Kalispell, MT
HI Moose!
I can't explain it any better over here so I'll give these guys a shot. Your engine looks good over at bonusbuilt - same color as the merc I put back in my 48.
edit: Never mind, I can't shut up. You described it right - you should be right on. If you had the head off you'd see the piston at the top of the cylinder and both valves shut at TDC.
ON the exhaust stroke you'd see the piston at the top of the cylinder, but the exhaust valve would be open.
There will be a point where both valves will be open a little at the same time. This overlap is intentional and is designed into the cam. Having the exhaust closing slightly after the intake begins to open helps the cylinder draw fresh air/fuel into the chamber by the vacuum created as the exhaust gasses are pushed out. That's the theory at least.
I can't explain it any better over here so I'll give these guys a shot. Your engine looks good over at bonusbuilt - same color as the merc I put back in my 48.
edit: Never mind, I can't shut up. You described it right - you should be right on. If you had the head off you'd see the piston at the top of the cylinder and both valves shut at TDC.
ON the exhaust stroke you'd see the piston at the top of the cylinder, but the exhaust valve would be open.
There will be a point where both valves will be open a little at the same time. This overlap is intentional and is designed into the cam. Having the exhaust closing slightly after the intake begins to open helps the cylinder draw fresh air/fuel into the chamber by the vacuum created as the exhaust gasses are pushed out. That's the theory at least.
Last edited by mtflat; Aug 3, 2005 at 01:43 PM.
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