Technical GHS 49 Ford- Low Compression After Rebuild

The marks look okay however replacement gears and a replacement Cam shaft can still make valve to crank timing incorrect. I always use a degree wheel and make sure Crank to Cam is dead on.
The Wizzard

 

I believe those were the original. It did not appear like the motor had even been torn into before and we used the original parts.

Can the crank gear be put on backwards? With a different mark on the back?

Edit- I asked the above question because I don't want to pull it off if I don't have to.

 

Is it just me or does that gear mesh even look right! Those teeth seem to be jammed up!! The crank tooth to the far left even seems cracked.

 

I can get more pictures if you guys would like. One of the hardest parts of projects like this is that this is my firs flathead motor I've worked on and they took it apart before I could really acquaint myself with it.

 

Gear mesh looks fine to me. I don't believe you can install the Crank gear backwards and have it flush as it is to the cam gear due to the relief cut in it on the Front. Also I have never seen a crank gear with a mark on both sides.
The Wizzard

 

Well, now I'm wondering if we have a ring issue. We've got about 40psi on all cylinders. So, I have a hard time determining if that is due to a slow moving motor, or actual low compression.

Looking back, it was spinning at 60rpm or so. Can anyone give me a ballpark of what their 6v setup spins at when cranking. I'd love to have a benchmark. I think we did get it faster than 60rpm after replacing the solenoid. I'll have to go back and read what Wizzard wrote about the starter.

 

Get some jumpers and spin it with 12V, just for the hell of it. I think, though, that both the low compression numbers and the slow cranking need to be SYSTEMATICALLY addressed before you do anything else. You are now heading toward a complete assembled motor that will have to be torn down again.

 

How about putting some air into the cylinder that has no compression and listen where the air is escaping ?

 

By all means, this is called a Leak down test. Very common around the Race Track and in most repair shops. It will be a good teaching experiance for the Students. Diagnostics is key to repairs needed before any repairs. If you don't have a degree wheel and still think cam timing is off do a T.D.C. and check valve gap.
The Wizzard

 

This is General Cam timing info;
Before you go any further on cams, we need to look at the piston as it pumps up and down and what the valves are doing.

1. Power stroke. The piston is at top dead center, intake and exhaust valves are both closed and the spark plug has just fired. The expansion of the ignited fuel/air mixture forces the piston down. Before the piston reaches bottom dead center, the exhaust valve starts to open.
2. Exhaust stroke. The piston is at bottom dead center and starts to come back up. The exhaust valve opens fully and starts to go closed. Before the piston reaches TDC, the intake valve starts to open and the exhaust valve is still partially open.
3. Intake stroke. The piston is now at TDC, both the intake and exhaust valves are partially open. As the piston travels back down the cylinder, the exhaust valve goes fully shut and the intake valve goes fully open and starts to shut.
4. Compression stroke. The piston is at BDC and starts to travel up the cylinder. The exhaust valve is still shut and the intake valve goes fully shut.

You’ll notice that during the piston travel, there is a time when both valves are open. This seems counter productive, but it is necessary for optimum performance. This is a term called "valve overlap".

 

You should have some valve gap on both valves on Power stroke at T.D.C. on all cylinders.

 

So, I get so distracted that I sometimes forget what I've already done. Back on post #24 I mentioned that we did do a leak down, but only of 1 cylinder. When we pressurized cylinder 1 we most noticeably had air coming out from the carb. This is why we went back to check the valve timing. The kids had set the lash just recently.

FYI, we did send 12v to the starter and it didn't help a ton.

With the intake off I just verified that we have valve gap on both valves on the #1 cylinder, TDC, Power stroke. I also just redid the leak down test myself and it is all coming out the intake runner. So... valves must not be seating for another reason. I'll have to get the head off and take a look... Can the springs/guides/etc be installed in such a way that the valves don't seat? I'm just thinking ahead as to whether this will be a valve seat issue, or an assembly issue.

 

With the plugs out of all 8 and some oil in the cylinders and 12 volts to the starter and the ground to the block that should spin like crazy.
As an aside I recently had experience with a 305 chevy with 160 lbs on all drivers side cyl and 30 lbs on the pass. It seems some A hole assembled the pass.side with 350 valves, .100 larger than 305 valves. Engine ran with a vibration but it ran. So anything is possible in the assembly of anytning mechanical.

 

You've said that the kids set the valve clearance, but have you personally checked them yourself ? Since the intake is off, maybe now is the time to check them before removing the heads.

 

had this happened to me on a Chrysler 6 I replaced the head gasket but before I put it back togeather I lubed it up with marvel mystry oil and all of a sudden it had no compression ran it around to some of my older friends and they told me 1 tea spoon of boraxo in each cyl , pull all of the plugs and turn it over 20-30 times and repeat it mine went up to 60-70 lbs and finally started runn it alittle 10 mi or so drain the oil and hopefully all of your problems will be solved good luck DWBLIETZ

 

So, I was watching them pretty closely when they did it, and I did go back and check cylinder 1. I've got at least .010 clearance on the intake valve, TDC, #1 cylinder, yet that is the cylinder I checked and it had air coming out the intake on the leakdown test. So, the valve isn't touching the lifter, yet there is still air coming out of the intake. So I need to check the valves that they are seating correctly. Or moreso, why they're not seating..

 

Could be poor seat or valve finish (or rust on freshly ground metal) or valves sticking in guides...anyway, there is something bigger than poor cranking speed happening.

 

What about the incorrect valve or guide going back into the incorrect cylinder? I would not be surprised if the kids mixed them up, but either way, the clearance was correct...

 

Got the head off. I cannot see a glaring problem, but the intake valve is obviously not seating.

 

Besure to squirt lots of oil into those cylinders, with all the cranking and no internal oil pressure lubing those rings and walls bad things can start to happen.

 

As long as you have the head off try this. Open the valve, paint some bluing on the seat, get some lapping compound and a suction cup lapper and close valve and try and to rotate valve enough with the tool to grind off bluing. Then you will be able to see if valve and seat grind match. try both valves in that cylinder. It might be impossible to turn valve but it's worth a try. Worst case is disassemble guide and spring etc Ralphie

 

I'm a big believer in Lapping compound. I also make sure it all gets cleaned off. It's way to abrasive to leave on anything inside a motor. My thoughts are, it's time to double check all valves. I'd do that by setting the motor with head gasket surface level and turn motor till I had gap at lifter and squirt solvent on top of valve and watch for them to leak into ports now that you have the Heads off. Way way back when I was just cutting my Teeth I was taught if you can't turn the Motor by hand with a flywheel tool you aren't going to spin it fast enough with a starter to fire it up. Maybe give that a try and see how things feel.
The Wizzard

 

Well sadly, we are wrapping things up and this project might not get worked on for a few months. Stay tuned...

 

Ahh, Summer brake. Yee Haa. Don't worry we'll be back for Class come Fall.
The Wizzard

 

WE'RE BACK!

So, all new kids on this project now...

That said, we reinstalled the head, leak tested cylinder 1 and reconfimred that air is billowing past the intake valve and now we have removed head #1 again.

Perhaps the students previously ground the valves at the incorrect angle? The lash is perfect. Maybe we'll pull all the valves on that side for now, hit them with blue dye (and the seats?), and give them all a good lash.

We had low compression on all cylinders. Like 20psi on all except 80 on cylinder 2 if I remember correctly.

 

Way way back when I was a bit younger and rebuilding Flat Heads was common place we had a brass plug we used in the Guide hole when doing a Valve Grind. We would slip in in place after grinding the Seat, the center hole was correct for Valve stem. After facing the valve we would always lap the valve to it's seat then kiss the valve stem with Cam in proper position to get lash. Adjustable lifters weren't common replacement items. I think adjustable lifters added another $10.oo to a rebuild then, that would be about $200.oo in today's money. Bottom line is always lap valves to see where the seat falls on the valve face. That will tell ya how good your contact is.
Welcome back
The Wizzard

 

So, slowly but surely we are lapping valves. They definitely were not right. Lots of low spots visible after a little lapping. We've been back and forth between the class and shop so it is a slow process.

 

Well, it's been a while... We lapped the valves. They looked great, in my humble opinion, but when it went back together, we still had no compression. I had them assemble the valve on intake #1 and I poured water down the intake runner and the water seeped out from around the valve. Now, the lapping job looks really good, but obviously it is not sealing. I'm looking for a next step? Grind the valve seats again?

 

Do you know what angle the valve and seat were cut at?

Can you get a pic of each after lapping?

And when lapping, it shouldn't take much on fresh cut valves and seats.

When they did the seats, did you verify the pilot tool was a nice fit, I wonder if it was loose and you "egged" out the seat?

 

Sadly the seats were done like 3 years ago, so I cannot verify what happened. We'd have to borrow a new pilot tool. We borrowed the last one. Both should have been cut at 45.