Y Block Help Needed

Thanks Tinker. The heads have been rebuilt not long ago, so I'm assuming they are good. That said, if I pull it apart, I will check the heads as well to make sure that they are right.
 
A couple of things about this post have me wondering. You mentioned that the "mushroom shaped" valve on the carb can be seen moving in 1/16th when the RPM is increased, but any spark control valve I've ever seen is built in a way that you can't easily see the diaphragm. Is it possible that someone has installed a power valve instead as they have the same thread and look similar? The other thing is that you have stated that the initial timing is set at 25 degrees, and I'm wondering why it does'nt kick back on the starter with that much initial. Also, if the distributor is the original loadamatic, you will have no advance with the vacuum line disconnected as there is no mechanical advance provision. I still think your problem is either the carb or intake manifold. Good luck : Bruce
 
A number of years ago I had the exact same issue as you with a new rebuild with all new parts on a stock Y block. Would not idle right, low compression and low vacuum. I rebuilt it myself so I knew it was put back together correctly. Drove me nuts for over a month and one day an old Ford mechanic told me to reset the intake valves to .035 or .045 and see if it runs any better and if the compression and vacumm would come up. Well it ran alot better and the compression and vacuum did come up significantly. He then told me I had a bad camshaft! This was a new camshaft that I installed at the rebuild from a reputable company. I removed the shaft and sent it to a another well known camshaft co. to be checked. They called me and told me that the intake lobes on the cam had not been properly ground at the factory and that was causing all my problems and it would never run right the way it was. They reground the cam, I reinstalled it and it ran perfect. Compression came up to 165 on all cyls and the vacuum came up to 22. The machine shop that did all machining for me said they could only remember one other time they had encountered a bad cam in the 60+ yrers they had been in business. Hope this is not your problem but the symptoms are very similar.
 
I came across this twice first time it was a 454 that came into the garage where I worked.we worked on it for days of and on the motor had been heated and rebuilt.the valve springs were collapsed.whoever rebuilt the heads never saw it.i rebuilt a 351m for my sons truck I had a parts engine from a cube van the cam looked like new and mine was just fair so used it.like you I had 11 vacuum.tried everythink under the sun in the end it was the cam.it was a ford cam and I never found out what it was used in.it was a pig in the truck and I cant imagine what it was like in a cube van.
 
I have to drop off the starter at the rebuilder today, but when I get it back, I will try a compression test with the intake valves set around .040" and see what happens. I don't know any other methods to test for a wrong cam, but I'm certainly open to suggestions. I've built a couple engines with a fairly big cam, and while they have a 'lope', they don't shake like this one does. It's just not quite right.
 
The only way that I know of checking the cam in the engine is to degree it in with a degree wheel, when I did that before shipping mine off to be checked I found that the intake valves were closing at different degrees of crankshaft rotation on each cyl causing an eratic running engine. Degreeing a cam is a pain in the rear and time consumming and requires special tools. Looking at your picture of the timming chain it appears to me it has a fair amount of slack/play in it and if so I would think that engine has not been rebuilt recently. If it has been rebuilt recently someone might not have replaced the chain when it was apart thinking it was still ok. One other check of the cam would be to check the lift of the cam lobe with a dial indicator at the rocker arm or the tip of the push rod, this would tell you if a lobe is worn down.
 
Thanks Wellcraft. I have a degree wheel and dial indicators, so I will work on that while I'm waiting for my starter to be rebuilt.
 
how I checked the cam on the 351 before I tore it down was to check when the intake valve starts to open.you have to have a tight timing chain to get it right since mine was new it was no problem.you insert a feeler gague on number 1 cyl,intake valve and turn the engine over slow until it pinches the gague needs to be close fit so it will catch the second it moves then read your degrees on the damper pulley.intakes open on most stock around 18 degrees a tuneup manual will tell exactly.my 351 cam opened at 30 so I had my answer.
 
Since you have the front tore down you might as well replace the timing chain, it does look worn as mentioned. That is unless your going to pull the engine and do a freshening of the engine :].

Best of luck.
 
I will definitely replace the chain while I'm in there. Thinking out loud, I will probably check with the degree wheel before and after the new chain.
 
As it relates to compression and vacuum it's very important at what degree the intake valve closes because if it closes to late essentially you are pushing the intake charge back out the intake manifold as the piston starts up to TDC. And to compound the problem if all the intake lobes are not the same you have a fluttering vacuum and erratic compression.
 
After all this discussion, this may sound like over-simplification, but I'd be pulling the intake manifold and making sure that the previous builder used the correct gaskets. All 1954 and some '55 heads/intakes had much smaller ports and if you used the later '56 and up intake gaskets you would almost certainly have vacuum leaks. Bruce
 
When I was a kid, dating, I had a '55 'bird. We're talking 1972, and I'm still not over that car, but that's another story. Stick and overdrive. One night at my girlfriends house (still have the girl, car long gone) I started as normal and got a funny backfire. Thinking I'd just let go of the key too quick, I re-tried, and when it started, since I'm a Model A guy, I knew immediately it was running way retarded. So I got a wrench and advanced the timing and headed for home, about 20 miles away. Long story short, I knew what was going on with the timing chain, and I had to stop 2 more times on the way home and advance the ignition. Obviously with 3 teeth off, it was running really rough by the time I got it home, but, it got me there fine. Next day we replaced the chain and off we went as good as new.

Good luck on the T-Bird. Wish I had one. 2 Model A's and out of $$$ and space.
 
Thanks Darrell, I've ordered the shop manual, but it won't be here for another day or two.

Bruce, I agree that it seems like it could have a bad vacuum leak at the intake, but I tested with propane and carburetor cleaner with it running, then followed up with a smoke test and could find no signs of any leak.

Jim, though I don't own one right now, I'm a Model A guy too and know what you are talking about. Anywhere near the specified 6-10 degrees of initial advance, this thing definitely feels retarded. You have to get into the 40+ range before it gets too advanced, making it difficult to start.
 
Keep in mind this engine only has an avg.105 lbs. of compression. Per the book min psi for this engine is 130lbs. With that in mind there are four key areas that can cause this, bad pistons/rings, bad valves, bad valve timmimg, and bad cam. Yes there are a few other areas that could have an impact like blown headgasket but that would have already been discovered,ie, water in oil/oil in radiator, very low compression on several cyls. A bad intake gasket would have no impact on compression, just think of it this way, what if the intake manifold was not bolted to the engine and you do a compression test. The reading would be the same with the manifold off or on unless there was a major obstruction inside the manifold that could not be seen.
 
Wellcraft, all good points, and that's why I was expecting to see the cam oriented wrong when I pulled the front cover last night.

I have a receipt for the reconditioning of the heads, due to drivability issues, so I'm going to rule out a valve or head issue for now.

With worn rings, I would be expecting smoke out of the tail pipe and blow-by from the breather, and I have none. They may not be perfect, but I don't think they are bad enough to make it run poorly. Plus, I wouldn't think bad rings would cause the timing to have to be that far off.

The timing chain has some wear, but it looks to be within the Ford spec of 1/2" of play. Not ideal, but I don't think that it would make the vacuum 1/3rd of what it should be. I could be wrong about that though. It will get a new timing set regardless of anything else that is found.

That leaves me with the cam, opening and closing the valves at the wrong time. Based on receipts, several mechanics have tried to solve this, but no one has. I do not see where anyone has gone as far as actually checking the cam. A bad or wrongly ground cam seems like a long shot, but what else is left?

I know that it's sure nice having the help of the Ford community.

Bobby
 
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