I have a 79 F-150 4x4 with a one year old rebuilt 400 with less than 10000 miles on it. It is supposed to have badger flat top pistons in it with a compression ratio of somewhere between 9:1 and 9.5:1. I haven't been happy with the performance over stock of this engine (I've got all the aftermarket goodies on it: carb, intake, timing chain, etc.). I have noticed oil around the plugs so I decided to do a compression test... Here are the results:

#1 - 109
#2 - 110
#3 - 132
#4 - 142
#5 - 134
#6 - 88
#7 - 105
#8 - 142

After researching, these numbers do not sound good. What do you guys think?

 

I did another test, this time with throttle wide open and got better results on #1, #2, and #7, but #6 is still really low...

First Time: 2nd Time:
#1 - 109 #1 - 137
#2 - 110 #2 - 140
#3 - 132 #3 - 132
#4 - 142 #4 - 140
#5 - 134 #5 - 135
#6 - 88 #6 - 87
#7 - 105 #7 - 130
#8 - 142 #8 - 142

 

Does the engine miss at idle? Have you pulled the plug wire off of #6 and check to see if there's any difference in the running of the engine?
Could be a burned exhaust valve on #6.

 

If your readings are good? #6 is dead. One of the things to check is valvestem height. Pull valve cover and pull rocker arms and do a rough measurement and see if valve is sucked up into head or burnt vlv?? another thing is to pour some oil into chamber. re comp test and see if it comes back up on compression. If it comes up just a little or nothing its your head. IF it comes up alot need to check piston for problem, btm end?pour about 2 cap fulls of oil into cylinder. your engine oil cap on a normal engine oil can should do. Just did this with a customer and said the engine was still new but this is what we found. had a cyl at low 80's comp and found a sucked up valve in head. bad luck for my guy.

 

Ok so I did another compression test on the engine (it was cold) and then added the oil to cylinder #6 and the compression did not change when I did the test again... Does this mean that a valve is bad? O and I called the place where I got my engine to ask about the warranty, and they said it had a 3 year 24000 mile warranty. Ok great. Then I ask if I can just bring them my pickup and have them fix the engine. Nope. They will charge me labor. WTF? Isn't that what a warranty is for? Needless to say they will be getting a pleasant call from me later...

 

Did it ever run good ? Where did it come from ?

 

I bought it as a long block from a local shop. It "supposedly" has badger flat top pistons with a 9.5:1 comp ratio and they said that this engine would have twice the power as the old one. I can't honestly tell much of a difference in power, let alone twice the power. The guy that sold it to me kept telling me that it had a cleveland camshaft in it. Well come to find out, that meant that it has a stock cam... problem 1... It does have a nice double roller chain in it though. After I got the engine in and running (vacuum leaks fixed, distributor in the right slot, and carb tuned) (oh and the timing chain on the engine broke when the engine first fired and then back fired) it has seemed to run pretty good... I am just at whits end with this engine as I should have just rebuilt mine instead of donating it as a core for this block...

 

Yea, anybody that says "it had a cleveland camshaft in it" obviously has no clue what he is talking about.

 

I think that I am starting to understand that now... the problem is that I wasn't as informed about these engines when I bought it as I am now so I never asked the questions I needed to. Now I'm stuck

 

didn't change. well my guess is your head is bad. did you check the valvestem height. have to pull the rocker arms off and do a caliper check is usually a quick way to check on stem height and valve sucking up in head. On the cleveland cam, which cleveland cam is the question? yes you can run a cleveland cam? 351m 400 and 351 cleveland are a common cam between these engines but need cam cut for your applicaition and cubic inch. Sorry about the troubles your having and hope we could help. some projects go easy and some just kick you in the nutz. doesn't look like your feeling well. any more questions drop a message and hope to get you rollin soon.

 

Well I have some good... I guess... news concerning my engine. The machine shop said I could pull the heads and bring them in and they would go through them or just give me new ones free of charge. I guess this company is looking up a little bit as my warranty expires on the 13th of this month!

 

So I did a third test, this time both wet and dry on all of the cylinders, and #6 is still bad, but that's not why I'm posting. My question is... all of the cylinders were within 10psi of each other (except 6) for both the wet and dry tests. The wet tests all read about 20psi higher per cylinder. The machine shop said that all compression tests will read higher with a little oil squirted in the cylinder. Is this true? I thought any change in numbers meant there was some ring problems. Is a 20psi higher reading ok? Thanks

 

That right there might be your problem with #6. you mean the timing chain broke witrh it runnning?? it may have bent a vavle.

Most rebuilders warrentys do not cover labor to install.
Take it out and take it back to them.
Then on your new or fixed one check the compression and spin test the oil pump and read the pressure before you install it.

 

On the higher compression is caused by a smaller chamber. smaller chamber means higher compression. oil has volume and it takes up some
CC's in the cylinder. also on the ring end gaps will probably seal totally and not work through as quick as a gas meaning air fuel. oil is thicker! this little test is just a troubleshooting procedure that helps steer you in the correct direction. If your piston is bad you will see some different numbers for sure. hope this helps and I see your thinking and the lights have come on.

 

I thought the PSI should be no more than 3psi diffrence from the highest comp. cylinder to the lowest. 10psi is alot