Y Block Help Needed

[countrysquire]

I hope I'm posting this in the right forum, please move it if I have it in the wrong place.

I just picked up a '55 Thunderbird that was restored a few years back, but has been sitting for the last year or so. Once I got it started, there was a pretty healthy gasoline leak from the pump, no doubt caused by the upstream electric pump. With the electric fuel pump disconnected and a new stock pump in place, it's running again, but it doesn't idle well. New plugs to replace the fouled ones didn't help a lot. I connected a vacuum gauge and it is between 10 and 11 inches hg, which seems awfully low. The timing seems to be advanced well beyond the 6 or 8 degrees that it should be, but retarding it makes it worse. When you rev it, it seems smooth and as powerful as you would expect, with vacuum in the 22-24 range.

The previous owner kept receipts of all the work that had been done, and it looks like a couple shops have tried to resolve similar issues with it. There has been a valve job with the heads resurfaced, new intake gaskets, carb overhaul, Pertronix ignition, etc. Compression is a little low, but consistent at 105 psi or so. The valves were set a little loose, so I reset them at .020 but that seemed to make the vacuum drop an inch or so. There is zero blow-by and no evidence of oil on the plugs, so I think that the rings are good.

Finally, sometimes it will idle as long as you like at 7-800 RPMs and is almost acceptable. Other times, one of the secondary barrels fills with fuel, eventually killing it by flooding. It has the original Holley 4000 teapot carb, which I have no experience with.

Anyway, it strikes me as having a vacuum problem that no one has been able to find as well as a carburetor issue. This is my first Y block, but I wouldn't think that it would be much different than diagnosing any other engine. That said, it's kicking my butt and I'm having to reach out to the experts.

Any help is appreciated.

Thanks,
Bobby

[Charlie Stephens]

Long shot, any of the plug wires mixed up? It is rough to work on a car when you don't know what was changed last.

Charlie Stephens

[countrysquire]

Thanks Charlie, I'm headed out to check that now. Maybe they did it in the newer 15426378...

I'm experimenting with things, and it looks like when the secondary butterflies open that's when it fills with fuel and kills the car. I don't know if this is because of the vacuum issue or not.

I just took it for a four mile ride at about 50 mph and it's missing at all RPMs. Placing it in 'Drive' knocks the RPMs from about 800 to 450 or so, barely enough to keep it running. I pulled the valve covers back off to make sure that all the rockers were moving as they should, and that looks good, but I haven't gone as far as doing any measuring. Also, there's a receipt for pulling the timing cover to check the timing chain, so I *assume* that is good. Still checking and looking and appreciate the help.

[scicala]

If you actually saw fuel filling up one of the rear barrels of the carburetor, then I would say you have some type of issue with the carburetor. There is a short brass tube that goes from the throttle body to the float bowl that has an o-ring on each end. A common place for leaks that could fill the one rear barrel.
Have you tried to adjust the idle mixture with the two screws on the front of the carb at the base ? See if the vacuum increases. Other possibility could be a vacuum leak somewhere. Even if the ignition timing was 20 degrees BTDC at idle, this would not cause low manifold vacuum.
If it comes down to the carb, I just finished restoring a correct original one for a 1955 Thunderbird. A rare carb though because it's a different part number than the passenger car carb.
Let me know if interested. Sal Cicala

[countrysquire]

Since the last post, I have reran the valves to make sure that they are at .020 and done a compression test. All the cylinders were between 112 and 128. Not high, but I would like to think it's enough to pull more than 9 inches of vacuum. What I keep thinking about is the timing. The marks on the balancer run from TDC to 10 degrees (I think). However, it wants t run at about 2.5 inches past that, which I would estimate about 25-30 degrees. Advancing it from there makes it ping, retarding it to the specified 8 degrees makes it feel very sluggish. When it's at TDC per the balancer, the rotor is pointed right at #1. One of the shops that worked on it pulled the timing cover to verify that timing hadn't jumped. Still, it sure makes me think that the cam is not synced up with the crank like it should be.

[40cpe]

Sponsored Links (Register now to hide all advertisements)

The cam and crank marks are a certain number of links apart on the timing chain. I wonder how many shops understand that. It won't run with the marks lined up with each other, so maybe they got it right.

[Tinker]

Clean your plugs, run the crap out of it and shut it down quickly. Pull the plugs and look at them.

My understanding is that y blocks like advanced timing. My initial right now is around 12+ degrees, 35 advanced. This is after taking it down some. 57 292.

***at lunch today I put a light on the motor. I was a little off on my numbers, 8 initial and 35 full advance. After I get all the wiring done I will have to play around with the retarding the timing and see how it runs. Have driven it and it hauls a$$ with this setting***

You want about 18" vacuum. Check leaks, set timing advanced some, adjust carb to best vac, then adjust timing again.

It sounds like you have decent compression. I would look at the carb or you ignition system and timing.

One last thought is the 55 distributor and advance. Search it a bit.

[Tinker]

Another thing you might want to do is make sure tdc and the marks on the pully actually match up. They do slip over time. There are ways to do this without pulling the head by using rope or a piece of tie wrap. It will not be 100 percent but you will be able to see if it has slipped 10 degrees or more.

Best of luck.

[countrysquire]

Thanks. I pulled the plugs after driving it and they looked good, nothing fouled like you might expect with a dead cylinder. Also, the balance is new (they charged the previous owner $350 for a new balancer!!), and when it is at the TDC mark, both of the rockers on #1 cylinder are 'loose' and the rotor is pointed at the #1 wire.

[darrell]

I would think the trouble remains in your carb.take it apart and blow out the passages and check for broken gaskets o rings etc.if you have power brakes plug the hose as well as wiper hose to see if you have a vacuum leak first.

[countrysquire]

Would a carb issue cause the vacuum to be half of what it should be? I'm thinking that I have an issue in addition to carb trouble.

I'm still puzzled why the the timing has to be so far advanced for it to run. I had mentioned before that when the previous owner had it in a shop (foreign car shop, don't know how much they know about Y blocks) that they pulled the timing cover to check it. It could be that they were expecting to see the two dots on the gears lined up, which I understand is not correct for a Y block. So it may or may not be right. That said, with the balancer at the TDC mark, both of the rockers on the number 1 are loose, so the lifters must be pretty close to the bottom of the cam lobe. Also, when at the TDC mark, the rotor is pointing to number 1 on the distributor, but I guess that you can stab the distributor in any orientation.

I'm going to pull the rocker shafts this morning to make sure that none of the pushrods are bent. They spin freely when relaxed and all the valves look to travel as far as you would expect when the cam turns.

[Ole Don]

Congratulations on becoming a Y block owner. A Y block is like any other engine, it needs compression, fuel and fire to run. Looking for a high vacuum reading with an unknown cam is futile. My car idles at 11 inches, on a good day. The cam is Iskenderian, I love it.
Any Y block runs better when timed with a vacuum gauge or by ear. Correct cam timing is, when looking at the cam drive, the colored links, or dots, should both face to your right, with 13 pins between them. If it runs down the road, that part is correct.
Early solid pushrods bend easy. Straighten them with a hammer on a hard surface.

[countrysquire]

Thanks Don. It does run down the road and doesn't run horribly like if the cam was way out of time. Fact is, if it ran great I would have never put a gauge on it. No idea what kind of cam is in it. I'm about to check all of the pushrods and then adjust the valve lash again. .020" cold is correct, right?

[Y-Blockhead]

I agree with everything Ole Don said with the exception of the push rods. I would recommend if you find bent solid push rods to go ahead and replace them with new tubular ones.

I have a Clay Smith cam in my 312" and I can't even come close to stock timing specs.
It idles best at ~14 inHG and when checked with a light it is at 16° BTDC. One thing to remember when running this much 'initial' advance is to check and limit your 'total' advance.

[Tinker]

I want to say it is 12 pins not 13 on the timing chain.

[Tinker]

If your rockers are worn a little you can use the quarter turn method. Tighten to zero lash, then backoff a quarter turn.

http://www.jalopyjournal.com/forum/s...d.php?t=521955

[countrysquire]

Update: Pulled the rocker shafts and ensured that all of the pushrods are straight. Reset valve lash at .019" with everything cold. Started back up and valves were quieter, but vacuum now in the 7-8 range. The previous shop had it set at .035", maybe in an effort to increase the vacuum, not sure. Anyway, it still has the same miss. I did notice that the rotor had a ton of play (the shaft itself seemed fine), so I will see if I can find another rotor that fits better.

I did make a discovery that will hopefully lead to a solution. I scanned all of the inlet ports on the exhaust manifolds and realized that there's a problem with #5 & 6 cylinders. The other six cylinders were between 400 & 425 degrees, while #5 was about 190 and #6 was 285. Both cylinders were getting good spark and the plugs were not fouled when I pulled them yesterday. Compression of both cylinders were in the same range as all the others, so I think the issue is that that corner of the engine is not getting enough fuel for combustion to occur. That has to point to either a carb or intake issue, I would think, but would sure like some other opinions.

Thanks again for all of the advice.

[countrysquire]

Oops, the dreaded double post.

[countrysquire]

Did a test for vacuum leaks this afternoon with a homemade smoke machine, but didn't see anything leaking. I'm going to pull that valve cover again and watch the rocker movement on #5 closely.

[JeffB2]

Originally Posted by Tinker

If your rockers are worn a little you can use the quarter turn method. Tighten to zero lash, then backoff a quarter turn.

http://www.jalopyjournal.com/forum/s...d.php?t=521955

Y-Blocks are solid lifter cams,that only flys with hydraulic lifters.Zero clearance and solid lifters =