Weak #6 cylinder

[40Coupe]

and appreciate your advice!


I finished troubleshooting a stumble I have had at top of RPM range after tuning carbs (twin 97 on Offenhauser intake) and rebuilding original ’40 distributor. I assume this weak cylinder will solve my problems!

Engine is a 59 which received new rings in mid 90’s and put back together. Valve train was not inspected to best of my knowledge- a fair amount of miles logged on this engine. Car was my Father’s daily driver in the 60’s & now mine to care for. Cam is a “race cam”- I assume 3/4 Isky based on age and history bored .120 over.

Vacuum is 14-15” at idle with 2” quick fluctuations- steady at fast idle and 20”.

Spark plug wire check indicates #6 cylinder weak..

Compression check warm:

1- 105

2- 115

3- 110

4- 120

5- 120

6- 50

7- 135

8- 130

Squirt oil in cylinder and Sea Foam in valves no help- imagine that .

Leak down: I can see both valves thru spark plug hole and stroked piston until both valves closed plus a tad rotation. Pressurized twice with 60psi air…quick leakage through exhaust pipe..intake silent.
No ticking at speed- assume lifter clearance is ok and cam not wiped. Valve movement appears significant.


Questions:

1) assume stumble/poor performance at load would be enhanced with a strong cylinder!

2) Is removal of intake and valve spring inspection the first move rather than pull head? Look for obvious issues and replace exhaust spring? Does/can lifter come out to remove spring?

3) Are mushroom valves/split bushings likely for this relatively large cam setup- (engine reportedly in Socal drag car prior to Dad’s purchase late 50’s)

4) Would vacuum smoothing at speed indicate worn guides (ref post on vacuum troubleshooting)? Leak down leakage appears very high.

5) Is a cracked seat/bad valve likely…crystal ball required

Thanks

Lane

[Russ/40]

Symptoms clearly tell me a burnt exhaust valve.

[40Coupe]

Thanks Russ...

I read so much about weak valve springs in the forum that wasn't sure where to start. I can see a large portion of the exhaust valve (aft valve based on intake runners) and it appears fine.
Maybe its tuliped or has a bad spot that is not visible.

Lane

[1937pickup]

I think you have problems with more than number 6-you compression readings are not as close together as they should be-they verry all over from 110 to 135 in the rest of the cylnders. I think they should be closer together.

[40Coupe]

Originally Posted by 1937pickup

I think you have problems with more than number 6-you compression readings are not as close together as they should be-they verry all over from 110 to 135 in the rest of the cylnders. I think they should be closer together.

Agreed

Entire valve train likely in need of an overhaul. Not sure how much cylinder wear there is- how loose pistons are in bore. I'll see how much ridge there is at disam this winter..and try and address #6 until another day. Not sure how I will be able to dress seat if needed with engine left in car...
Doesn't use oil or smoke but plugs are sooty...looks like excess fuel even after rejetting.

[Chris Nelson]

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It can be done in teh car, but the quality of the valve grind and the difficulty of doing it are a big question. The engine comes out easily. You should be albe to pull it in 3 hours if you do it by yourself. It sure gets easier to do a good valve job if the engine is on a stand. I would plan on doing all of them. Not just #6 as you do have some varying compression numbers.

[40Coupe]

Appreciate the advice....

I'm back to work on the '40 (Dad passed away in August and other builds and my son's activities kept me busy)....

I'm going to pull the motor- hard to keep the plugs clean with stock ignition and poor cylinders (significant ridges).

1) Assume radiator should come out and tranny stays in.
Does fan need to be removed as well? (59 motor- stock 40 deluxe sheetmetal)

2) How far forward is typical to clear input shaft in clutch etc?

2) Assume a stumpfy engine fixture will support the block on stand with no further support?

3) Any idea if these are mushroom valves? Any thoughts on design- typical Ford valves/springs?

4) These appear to be an adjustable lifter with one of them backed off (3rd photo). What keeps these locked? Any recommendations for a replacement set? Ol' Ron seems to indicate they are all bad from a few posts I've read. Suspect these have been in service since the 50's.

thanks....Lane

[JWL]

Yes, remove the radiator. Yes, leave the trans. Yes, remove the fan from the crank. About 6 or 8 inches will give enough clearance and twisting angle to remove. I always bailing wire or strap the trans up to maintain its position in relation to the frame before removing engine.

I don't know about a stumpfy?

Yes, those look like mushroom valves. No, those do not look like stock valve springs. Look much stronger than stock.

I would like to see the bottom of the loose tappet and the coordinating cam lobe.

[Ross F-1]

The clean edge around that piston (no carbon) is a classic indication of oil past the rings.

[Kurt in NJ]

It's time to push out the pistons, it looks like the lower cyl in the picture that the top compression ring is broken---the cyl by the blue dipstick shows a good shadow that is even all around(as much as the picture shows), the bottom cyl shows ring contact in just little streaks ---most likely from the ends of broken ring pieces ---if that is also the low compression cyl most likely that is a factor in the low compression

[40Coupe]

Originally Posted by JWL

Yes, remove the radiator. Yes, leave the trans. Yes, remove the fan from the crank. About 6 or 8 inches will give enough clearance and twisting angle to remove. I always bailing wire or strap the trans up to maintain its position in relation to the frame before removing engine.

I don't know about a stumpfy?

Yes, those look like mushroom valves. No, those do not look like stock valve springs. Look much stronger than stock.

I would like to see the bottom of the loose tappet and the coordinating cam lobe.

Thanks...I assume removing all the springs is first order, lifters, remove cam then last is removal of split bushings/guides is last- maybe I'll leave that to the machine shop...after reading all the stories here....of course that may be expensive. I'll post some more pics as I go.

Originally Posted by Ross F-1

The clean edge around that piston (no carbon) is a classic indication of oil past the rings.

Interesting..thanks- I would probably have tried just repairing the one valve but car wasn't reliable with constant fouling of plugs.

Originally Posted by Kurt in NJ

It's time to push out the pistons, it looks like the lower cyl in the picture that the top compression ring is broken---the cyl by the blue dipstick shows a good shadow that is even all around(as much as the picture shows), the bottom cyl shows ring contact in just little streaks ---most likely from the ends of broken ring pieces ---if that is also the low compression cyl most likely that is a factor in the low compression

Bad valve is #6 so lower piston is 5 and 7,8 are above. No honing marks in cylinder bore so any damage may have been from previous rings. 5,7,8 compression was some of the best! But..yes appears an overbore is in order...currently .125 over from what Dad had told me.

[40Coupe]

Motor out over Veterans day...removed the valves over thanksgiving and 2 pistons. Lifter that had adjuster back out has heavier scoring than the rest but in better shape than I expected. Haven't looked at the cam lobes yet. Looks like a set of lifters is in order...I assume these are hollow Johnson's and in service for 50 years.

3rd gear in transmission is well worn (inspected thru side cover earlier)- I'm thinking of pulling the tranny and replacing the gear and maybe syncro for 2nd (I have two spare trannies). I haven't researched removal.

Does trans come out with drive shaft or slide out on splines after unbolting rear clamping device?





A friend loaned me a pry bar (left) made from a Nissan tie rod with allen stock welded on for a fulcrum. I used needle nose vise grips and a prybar to pull the clips. The intakes were easier...they got soaked a bit longer (I suppose) since I pulled the intake. I was pleased to get them out after reading all the horror stories.



Is this a 1944 block? Didn't know there was production in 44? (59 is evident below)



Pic of Dad with the smoke (not his car)- assume just prior to Korea. I met his pal providing the hand signal..he said he's the last one left.

[RCM]

This post would give a nice tutorial.

[40Coupe]

Took a few years..but I got my new engine running over the last couple of weeks! I chose an 8ba block as a starting place as it was locally available. The block was machined to re-establish the bearing bores and the "stroker" crank from the 59 was reinstalled with 8ba rods and bearings. The Isky 1016 was removed and Pete provided a 1007b cam- the idle is nice with a lopey crackle (.360 lift/255 dur), sounds better than the old Isky cam. A 1.6 SS chevy intake valve was used with stock hollow light weight lifters re-conditioned by Pete. I wasn’t comfortable with an adjustable. Offy heads were chosen to match the 50’s period intake manifold- I setup a PCV under the manifold to the draft tube. Exhaust manifolds were aluminized by Jerry MacNeish and painted. Re-used the 40 ignition and generator set-up that have been with the car since the 50's.
The transmission gears were well worn- I bought new gears from Don’s antique auto in Sunol/Fremont which was a lot of fun- bearings, synchros etc were provided by Mac including an overhaul book.
Looking forward to driving the car again...thanks for the help!