Technical GHS 49 Ford- Low Compression After Rebuild

Well, as mentioned here in our build thread, we rebuilt the 8ba Ford flathead motor last year and, a year later, we are trying to start it. We eventually did a compression test on all 8 cylinders where we found we have 35-40psi on all cylinders except for #3, where we have essentially 0. Squiring oil does nothing. I'm pretty sure they put the timing gears on correctly. The green shop manual says valve adjustment?

What do you guys think? I'd hate to pull this all apart, but we need to hear this engine fire up!!!

Probably time for a leak down test...

 

Start by just pulling the intake...check clearances again then have someone turn it slowly (7/8 socket on the front of crank) while you watch. See if what goes up is coming down...then see if valves are seating firmly by pushing down a bit on a closed valve via sparkplug hole. Oil test is saying valves...closing, or seat issues...?
What sort of valve work did you do?

 

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HUH?????

 

"6 \{, ○◇tgdd◇9 [¤|♤666
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Sorry we don't speak Clingon here!

 

Good course of action. We lapped all the valves while the engine was apart. The students kind of "run the show" in that I have them try to assess and make the calls. We often learn from "our" mistakes. Sadly this project was going on while my attention was elsewhere, so I don't have as many details as I'd like. And all of the kids who did the work graduated last year.

We'll pull the intake tomorrow...

 

Sure sounds like tight valves.

 

They have begun to pull the intake! Thanks guys.

 

Don't click on that is a *CIA super script. Your Baked Alaska will then be able to spy on you.

*CIA = Culinary Institute of America.

 

Ok, we went in, we adjusted all the valves. Still low compression.

Engine rotation. This is the first 6v system I've ever worked with. I think the engine is just spinning too slow. Right now, with a full battery, we're only getting 1 rotation per 2 seconds. How does that sound?

 

That's 30 rpm. To me, that sounds a little slow.

 

Assuming battery is good look for resistance at all cable connections, feel over the cables and solenoid for hot spots. You might just have poor quality 12 V cables, drastically undersized, or an localized bad connection/bad solenoid. Most such problems will become way too hot to touch after a bit of cranking.

 

Yeah we did voltage drop tests, lost .2v to the solenoid, about 1v loss across the solenoid, and then another .3V+ down to the starter. So I have 6.4v, 5.3v at the battery while cranking, and like 3.8v at the starter.

Can the solenoid be rebuilt?

 

Buzz it over with 12 v and see what you have,,,,

 

We did, it spun faster, but still not enough. I think that 1V drop at the solenoid is killing us.

Maybe we can take it apart and clean it?

 

I can teach you how to adjust your fuel trims to match your air fuel ratio and knock count on an injected turbocharged car. As far as 6V positive ground system, they're a little before my time. So it helps to have some reminders. I've never even seen one crank before so I wasn't sure exactly how fast they should be spinning. Sure seemed slow to me, which is what we verified with the voltage drop test, even before Bruce posted. But we appreciate his direction and affirmation. Sorry to disappoint you Wizzard.

 

is the crank versus cam timing way off?

 

You know, I'm almost certain that it is good, but with high school students, they sometimes surprise you. We assembled the engine over a year ago. I'm pretty sure that I verified the timing as correct.

 

With that low of compression your starter should spin rather freely.
And if 12 volts isn't turning it fast enough then you surely have resistance in your electrical system.
Since this was built by students. It may be a good idea to remove the plugs and try it by starter and by hand. Just to make sure you don't have a mechanical resistance.


Sent from my iPhone using H.A.M.B.

 

Of late while watching the News I have to many times said "He'd have been better off Not to have said that". I come to the H.A.M.B. to relax, share and some times Learn. Today I should have headed my own advice but didn't and in turn Learned just a bit. My earlier remark was unnecessary and for that I apologies. I will also remove that post.
In today's economy we see most Schools removing Shop class as an option to students. I have been a Mechanic, builder, fabricator since before I could drive. I grew up with a Fix everything Dad. I am thankful gijo985 is willing to take the Job of teaching those that will learn anything Automotive. It can't be an easy Job.
His question from My point of view was just to basic. I forget that what I take for granite is not the same for all. Even a Teacher can have there time of need for a little help. At least his Students now know what a Flat Head motor is. Diagnoses is always step one and I'm sure gijo985 spends a lot his time doing just that. I forget just how blessed I am in growing up when and how I did. I think some times I am all done, Today I stand corrected. In the future I will try to work a little harder at thinking before I type a comment.
The Wizzard

 

just do a leakdown test and listen

 

look at post #3 for a picture
https://www.jalopyjournal.com/forum/threads/flathead-engine-gurus-help-with-cam-timing.682816/

 

Wizzard, I really appreciate your thoughts. Sometimes I do get very spread out and I post stuff on here before I've even thought about it. We currently have 3 SBCs being rebuilt, a 455 olds, 4g63t Mitsubishi turbo motor with a huge Holset turbo 880cc injectors, etc, getting ready to go in an eclipse, a twin turbo 3000gt that needs fuel tuning, an el camino being painted, and about 6 90s jalopys that we're trying to get running. So I get spread thin mentally.

manyolcars, I really do think we have the cam timing right. I remember the kids lining up the dots. Pretty straight forward. Especially when we were just recenly doing timing on that twin turbo dohc v6 motor. Two dots on some metal gears is a blessing compared to 5 points and a rubber belt that likes to jump. But we may check again, just to cover out bases.

I JUST now noticed that after the kids went in and redid the valves, they left off the intake gasket. Now, that isn't our compression or cranking issue, but obviously one we need to fix. If they take off the generator to get the intake off, maybe I'll see if we can peek at timing. We'd be part way there.

After installing a new solenoid (I didn't expect Oreilly's to have one) we still have too little juice, but it is much better. I actually heard a cylinder fire a couple time. Once exceptionally loud because the kids swapped two wires while pulling the plugs and squirting a little oil in today. I feel like we're making progress.

I do think a cylinder leakage test is the next best test. Try to pinpoint where our lack of compression is from.

Again, I appreciate all of your help. We get two 45 minute periods a day to work on all of the above cars and I typically can only give each student 2-4 minutes of my time. It's crazy, but it's worth it.

 

P.s. I can turn the engine over by hand, just by grabbing on the crank pulley and using some muscle. FYI...

EDIT-----
So, leak down test cylinder 1, got a lot of air coming out the carb. So looks like we're looking at the valve job they did, as well as valve timing.

Also, with about 60psi of air going into the cylinder I tried cranking over the motor to rotate it some and when it got to the compression stroke the starter couldn't even turn the motor with the 60psi in it... so we probably need to be looking at the starting system some more as we continue looking at the compression...

 

Looking forward to learning what the problem is. No rings at all?

 

F.Y.I. In order to have full current draw at the starter motor the brushes need to be in good shape to complete the circuit. High carbon track on comuntator or week brush spring will cause a week current draw and poor starter operation.
The Wizzard

 

I left the kids alone for 20 minutes... they now know that yhe torque specs for screw in rocker studs are not the same as the adjustable rockers themselves....

Lesson learned for them. I wish I had the facility for all my kids to build motors at the same time. Then I could just focus on one thing... thankfully this was our junk motor (given to a specific group of kids for a reason [and actually they're some of my better kids, just not my best])

 

HOW DID YOU GET THAT PICTURE??? I THOUGHT I HAD BURNED ALL THOSE NEGATIVES FROM MY ENGINE CLASS BACK THEN!!! Oh, I guess those aren't mine after all ; never mind.......

 

Well, I'm happy someone can relate. I have to remind myself how many things I broke in high school. I remember snapping a exhaust bolt off in my 390 FE truck motor. Had to pull the head to drill it out... And then on reassembly I snapped off a rocker arm assembly bolt. The exhaust snapped on removal. With the rocker bolts I accidentally stuck the long bolt down the short hole. Oops...

We're tearing the top/front of the motor down again this week. I'm hoping for bad valve timing. That'd be an easy fix.

 

Does this look right? There is a 0 printed in the crank gear.