I'm still a little wet behind the ears with this stuff, so bear with me. 25K miles ago I did my first rebuild when one of the pistons went sideways. Stipped it down and handcarted the block to the machine shop where they sleaved the cylinder, rebuilt the heads, and put in new pistons and rings. Took it home and put it all back together. Everything went fine except I ended up with a heavy duty preasure plate but standard throw out bearing. (Long Story) The result however was a lot of noise as the throwout bearing disintegrated over time, and I couldn't stop to replace it. This noise may have masked the problem I am now having, but I'm not sure so I don't know if I've had this problem since a couple of months after the rebuild or if it just started now.

Now for the actual problem. Sorry for the book! When I start the engine I get a noticeable vibration that I would like to attribute to a miss, but pulling off plugs one at a time doesn't seem to pin it down. I don't get the pfft from the exaust that you typically get when it misses. I have a vacumn gauge hooked up in the cab and I get some flutter between 10 and 16 initially and when I accelerate, but after it warms up it stays pretty much at about 16 +- 1. Although the vibration dies down once it's warmed up, it doesn't completely go away. On the other hand I seem to have plenty of power, but I may be a poor juge of this since I have only been driving since 89, in fact this is my first "car" Truck that is, 1977 F250 manual shift.

I've swapped out the pilot bushing thinking that might have died due to the missmatched pressure plate, etc.

I did a compression check and this is what I got:

115 129 125 144 128 128 123 120

All the plugs were mostly very clean and white, except two of them had a brown dot about 1/8" in diameter on the side of the post, but the rest was clean and white. This was on plugs 1 and 2. 5 and 6 had a little tinge of the brown, but that's all.

I apologize for the book, but I wanted to give you something to go on. Thanks for any clues and pointers. I may be a little late in starting, but I'm beginning to like this stuff in spite of all the ragging I get at work about how I should break down and get a new car...

Bruce

 

Starfire, I would check for a manifold leak first, since this is a newly rebuilt engine. Check all hoses, and look for a leak at carb baseplate.

"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)

 

Thanks thelonerangerxlt,
I had already gone thru the vacumn leak tests prior to this, I even went so far as to replace the valley gasket and the two carb gaskets. But just for safetys sake I went thru and rechecked all the hoses. I cought one minor leak where I hadn't cynched up hard enough on a cable clamp. Regrettably the main problem is still there. The bad thing is that it is likely to cause other problems if I don't get to the bottom of this. The good side, is that it still runs ok.
If you have any more ideas, please post!
Bruce

 

Hi,

How is the carb? Was it rebuilt also? Do you have the hot air stove box that directs warmed air from the exhaust manifold into the air cleaner when the motor is cold?

Since the problem becomes less noticable when it warms up I would look at the carb/choke settings and the air/fuel mixture?

Just some things to try....

-Brents

 

Hi Brents,
Yes it does have the hot airfeed to the air filter, and the door on the air intake does work. I bought a remanufactured carb from Monument when I did the rebuild, but I am beginning to suspect that there may be problems with it. I haven't decided whether to get a rebuild kit or get another rebuilt carb,or maybe a totally different carb like one of those eldebrok ones.
The only reason why I haven't pursued this direction yet is that the compression readings I got seem to indicate that there is something else going on here. Thankyou for your help, it is realy appreciated.
Bruce

 

I also had a vibration. I had my 400 rebuilt and it would idle a little rough and shouldn't. Between 1000 and 1600 it would shake. Had power and wasn't a miss. Changed carbs and nothing. A local speed shop said try the distributor. Switch it from an engine that ran smooth and it help alot. My dist. was worn and was throwing the timeing off enough to make it run rough. The shaft moved back and forth quite a bit. Maybe check this.

 

Thanks Carp,
I think you are right, I have been suspecting the ignition system. I'm going to start ripping into it shortly.
Bruce

 

I did a compression check and this is what I got:

115 129 125 144 128 128 123 120

Well I would have to say our getting your vibration from your mismatched compression readings
OK I would have to say by looking at this the 144 is the cylinder you had sleeved and the new piston put in. here's where it starts. Now if the next cylinder that fires is the 115 there's an imbalance. Big boom little boom Anytime you have more then 10# differants you going to have a mismatch.
I'd say pull the motor a part and have all the cylinder Checked for out of roundness and rehone if still within spec.and put in a new set of rings."This should have been done when you had it apart the first time."Anytime you take a motor down you should do the job right and fix's it as a whole not just what broke.
But you live and learn..

ShaZam

 

Hi ShaZam,
Thanks for the info. Actually I did do it up right when I had it sleaved. New pistons and rings and honed the cylinders. Lately I discovered some ignition problems, and decided to do what I had been planning. ie MSD6 ignition, coil and wires. Then the malory Unilite distributor. I still may have a prolem as you say from the preasure differential.
Thanks,
Bruce