Technical GHS 49 Ford- Low Compression After Rebuild

Are the guides and springs installed and tensioned then locked in place when you do the water test? Valve needs to be drawn down tight to seal.

 

Yes, agree with above make sure the guide clips are installed firmly. Also. Clean. All grounds bare (for sake of starting). Use fat 0 gauge wire and 12v to spin it. What are clearances on the valves? Are lifters moving or stuck in bores? Think of it as a pump. All cylinders had 35 on low crank ? can be 50-75 with a 4-5 spins and throttle open.

 

Are you sure the timing is correct cam to crank?

 

That's a problem, can't have both valve and seat at the same angle.

 

See post #30....

 

Hmm, now I need to dig through stuff and look.

 

Yes they were.

So for the flathead are the seats supposed to be a 46? Valves a 46? The old green manual says 45 for both, so that's what we did.

The kids did a ton of lapping. We have a wider margin than 1/16", but I figure that should help sealing, not hurt it. We can easily regrind the valves. I'd rather do that than the seats, on the installed motor.

Advice?

 

I am going through a similar thing with my newly rebuilt flathead. Tried to start it and it turned good but no fire. New everything, wires, battery, starter, dist., plugs, everything. No fire at all, 1 backfire once. Low compression readings on all cylinders with all new pistons and rings on a newly bored motor. The first problem I have found is the crank gear is on backwards and I have no idea how the builder ever got the cam to crank timing correct so anything from that point on is in question. I am at the point now where I have decided to pull the motor and disassemble it and look at everything he worked on. Going to put a new crank gear on reset the cam to crank timing and reassemble it and see what I get.

 

Do you have adjustable lifters? Were they properly adjusted when you did the leak test or was the cam holding the valve microscoply of the seat?

 

No adjustable lifters. We went through and ground everything to spec. All of the lash looks good. That I can confirm.

 

Ok, lets just assume the valves are doing there job. I personally would have changed seat angle 2 degrees from valve angle and tried to get about .060 seat width but that's just me. Don't matter. Ring seal and head gasket are the only other things to cause low Comp. Maybe cranking speed could contribute some but not so much. I know your motor has set for an extended time frame. Let's say the head gasket seal is 100 percent. I would then give each Cyl. a few shots of Marvel Mystery Oil so I didn't drag dry rings up and down the Cyl's. I do that to healthy motors that have sat more than a year before hitting the button, I feel it's just a good thing to do. That will also help seal the rings a good bit and boost cranking comp numbers.
The Wizzard

 

In case it was missed, our valves are NOT seating. So, we are left with grinding the seats again (engine in the car?) or if regrinding the valves would somehow help, we could do that.

 

You have fluid passing through the valves after lapping them? That sounds like a rough stone being used, loose guide for seat stone, and not lapping properly. If you have high spots on either part (face or seat) you can get a good pattern on the valve face buy continuing to spin the valve over the high spot. Forcing lapping compound into a low spot will also give the appearance of a seat pattern. Sounds like you need to do a closer inspection of what's going on between the valve, seat, equipment and operator.
The Wizzard

 

So, we're going to pull the motor out and get back to the basics. We didn't want to, but we've got to figure this out.

If we get new battery cables (6V) and our starts seems old and tired, does anyone know where to get a new one? Or a rebuild kit? I was having a hard time sourcing one.

 

Go to Early V-8 Ford store and put in this number. They are New not rebuilt. Item# 18-11002-6VN Also not real cheep but what's a guy going to do?
The Wizzard