40 V8 compression change all cylinders same time

[Craig CT]

Originally Posted by bubbas ignition

wouldnt worry so much in regards to the dots as i would tdc versus actual valve position....

x 2

[L78CHEVELLE]

Originally Posted by BUBBAS IGNITION

Wouldnt worry so much in regards to the dots as i would TDC versus actual valve position....

Wouldnt worry so much in regards to the dots as i would TDC versus actual valve position....
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Can you give me some more details of how to determine TDC with the head on and what is the valve position when TDC is achieved? Can I put a long thin rod in the number one spark plug hole and determine when the piston is at top dead center? Should the dot on the cam gear and the dot on the gear on the crank line up on top dead center? If the dots do not line up at top dead center on number one piston then I know the cam gear has slipped? I have never rebuilt a flathead engine or set the timing marks before.

[Jack E/NJ]

https://www.jalopyjournal.com/forum/...caster.542626/


Jack E/NJ

[tubman]

"L78CHEVELLE"- Don't take this wrong, but you do understand the concept of a "press-on" cam gear, don't you? From your "handle", I think you might be familiar with only "bolt-on" cam gears. Early Ford V8's are different.

[STEVE O]

I personally have never installed the press on gear in the early flatheads (done plenty Cummins diesels with press on gears) but reading I see in one article that the cam and the gear have a mark to index the cam gear to cam and of course the 2 dots for the cam to crank gear. Since it ran good to begin with the dots must have been right but the possibility of the cam gear slipping on the cam could have happened. I wish I could say but I don't know on these era flatheads how to find TDC without a head off.

[Mart]

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Before you take anything else apart, it might be worthwhile just taking stock of what is going on.

You have the intake off.

Number one cylinder is right hand side, at the front. Use the cable tie method to locate top dead centre on the No1 piston.

Observe the valves on either no.1 or No.6 cylinder. They should both be open by the same (small) amount.

This would be an indication that the cam and crank are in the correct relationship.

Link to thread describing tdc finding: https://fordbarn.com/forum/showthread.php?t=110405

Mart.

[L78CHEVELLE]

Thanks to everyone that has responded to my request for help. I have printed off the responses and will study them and try to come up with a solution to my problem. I first need to find out what the problem is and then see what my ability is to correct the problem and go from there. I will up date the post as I catch up to the suggestions I have been given.

[L78CHEVELLE]

Took the front of the engine off today. My 40 has the late production engine with the bolt on camshaft gear. The mark on the camshaft does line up with the mark on the crankshaft gear. Now I am even more confused. Has the camshaft worn down in 2,000 miles? I did use the diesel oil with Zinc in it since the rebuild. I did pump one squirt of oil in a cylinder and turned it over. Still got the 65 compression reading. Amy one got any ideas?

[Craig CT]

Originally Posted by L78CHEVELLE

Took the front of the engine off today. My 40 has the late production engine with the bolt on camshaft gear. The mark on the camshaft does line up with the mark on the crankshaft gear. Now I am even more confused. Has the camshaft worn down in 2,000 miles? I did use the diesel oil with Zinc in it since the rebuild. I did pump one squirt of oil in a cylinder and turned it over. Still got the 65 compression reading. Amy one got any ideas?

Hi L78CHEVELLE; If it's a faulty compression gauge that will take you back to carburetor and or ignition, Craig.

[Tinker]

If it's a new rebuild I'd suggest running it. Breaking it in on the bench is less effect then underload. If you trust your builder.



Think there was a post earlier on finding tdc with the head in. No marker on a stock 40s motor. You can make one. Find the compression stroke on #1 (thumb over hole), then the Basic idea is a stop (like a zip tie end) that you put in the plug hole of the head/cylinder and then rotate it till it stops (mark it on the cam pully), then rotate it the opposite direction till it stops again and mark it. The distance between the two is a rough tdc. A couple times is best. Or even better is with the head off and a dead stop.


There are better methods here, if I look. One idea was a spark plug that was hollowed out and a bent rod was welded in that would impede the piston from completing a cycle.


Either of these methods must be done by hand cranking. Never with the starter motor.


If your cam is off, it'll be apparent with the crank indexed to timing. Valves lashing correct...


Here is a barn version of a index. I use a timing bolt that has a welded point. Post #8

https://www.fordbarn.com/forum/showt...8503&showall=1




Just for fun.... Stock cam? or a regrind?




.

[L78CHEVELLE]

Stock cam that is new. Everything in the engine is new except the crank which was like new. Engine ran as designed for about 2,000 miles after the rebuild. Compression change and poor performance started about 300 miles ago and now the engine is down to 65 on each cylinder and very hard to start when it warms up to operating temperature. Valve clearance is 11 intake and 14 exhaust. Can some one tell me from experience a similar situation and cure from back in the day? The car is useless the way it is. Do not want to put a modern drive train in an original low mileage car. This problem is something odd for sure.

[BUBBAS IGNITION]

Originally Posted by L78CHEVELLE

I have a original 1940 85HP engine that has been rebuilt professionally about 3 years ago. The engine ran great for the first year and half for about 2,000 miles. Compression on each cylinder was 100 to 105. Now the engine runs poorly, misses, hard to start when hot, and is not reliable. I checked the compression today and every cylinder is 60 to 65 pounds. Valve adjustments are good. I am confused and discouraged. Can any one give me some options?

Been a few days watching this thread and we all went for the low compression, cam shaft etc. Looks like all is fine there so far . Lets look at the miss fire issue for a minute ........

[Russ/40]

Forgive me for asking, but you say the valve lash is .011" intake and .014" exhaust. What procedure did you use to position the cam for the lash adjustment? Did you make a valve lash adjustment before this problem arose?

[L78CHEVELLE]

I have the problem with the low engine compression and checked the valve lash as a possible cause thinking with a new engine the adjustments could have changed during the break in. The new rebuild has the adjustable lifters. I checked the lash on each valve by opening the intake valve on each cylinder all the way open and checking the exhaust while the intake valve is at its peak opening. Then turn the exhaust valve on each cylinder to it's peak opening and checking the lash on the intake valve of that same cylinder. I think that would be a fool proof method. Is my thinking wrong on this method? The compression was 100 or more on each cylinder about a year ago when I checked it for peace of mind. Gradually the engine has run worse and worse. I am thinking maybe the new camshaft has been soft causing it to wear down and the valves are not opening enough. I thought the Shell Rotella oil would have prevented that. Got the camshaft from a well know supplier in southern Ohio.

[JSeery]

Originally Posted by L78CHEVELLE

I am thinking maybe the new camshaft has been soft causing it to wear down and the valves are not opening enough. I thought the Shell Rotella oil would have prevented that. Got the camshaft from a well know supplier in southern Ohio.

If the cam was that worn down the valve clearances would have opened up.

[flatjack9]

Originally Posted by L78CHEVELLE

I have the problem with the low engine compression and checked the valve lash as a possible cause thinking with a new engine the adjustments could have changed during the break in. The new rebuild has the adjustable lifters. I checked the lash on each valve by opening the intake valve on each cylinder all the way open and checking the exhaust while the intake valve is at its peak opening. Then turn the exhaust valve on each cylinder to it's peak opening and checking the lash on the intake valve of that same cylinder. I think that would be a fool proof method. Is my thinking wrong on this method? The compression was 100 or more on each cylinder about a year ago when I checked it for peace of mind. Gradually the engine has run worse and worse. I am thinking maybe the new camshaft has been soft causing it to wear down and the valves are not opening enough. I thought the Shell Rotella oil would have prevented that. Got the camshaft from a well know supplier in southern Ohio.

The proper way is to bring each valve to its peak and then rotate the engine one revolution and then check your clearance. A quicker way is to bring a piston to TDC on the firing cycle and check both intake and exhaust.

[Mike in AZ]

Re-torqued the heads? Any chance of posting pictures of front gears and engine? Mike

[Russ/40]

Originally Posted by L78CHEVELLE

I have the problem with the low engine compression and checked the valve lash as a possible cause thinking with a new engine the adjustments could have changed during the break in. The new rebuild has the adjustable lifters. I checked the lash on each valve by opening the intake valve on each cylinder all the way open and checking the exhaust while the intake valve is at its peak opening. Then turn the exhaust valve on each cylinder to it's peak opening and checking the lash on the intake valve of that same cylinder. I think that would be a fool proof method. Is my thinking wrong on this method? The compression was 100 or more on each cylinder about a year ago when I checked it for peace of mind. Gradually the engine has run worse and worse. I am thinking maybe the new camshaft has been soft causing it to wear down and the valves are not opening enough. I thought the Shell Rotella oil would have prevented that. Got the camshaft from a well know supplier in southern Ohio.

I'm thinking the valve lash is off. Bring each valve to max lift and rotate another full turn. Then adjust the lash.

[Tinker]

What is the cam? maybe I missed it, sorry

[JSeery]

And valve springs, are they higher than original spring pressure?