In the last month the power output of my 300 has dropped about 50% .At first I thought the timing gear had lost a tooth and the timing had gotten off . The rattle is so bad I won't drive it any more. Have had several answers to the problem , such as bad gas, timing, carb, worn cam & lifters, worn valve train, etc. At low speeds it runs fine, but as soon as a load is applied it starts rattling .I have never heard what a motor sounds like with worn or collapsed lifters. What do I look for on inspection, or at this point is a motor change the answer? any help is appreciated!

 

first do a compression check. then check oil pressure.post what you find here.
Phillip

 

Finally got hold of a compression check tool . These are the totals from front to rear , 70 , 65 , 115 , 125 , 134 , 115 . All readings taken with all plugs removed .Cant find an oil pressure tester as of yet , I can make a good guess that on warmup oil pressure is up to about 40 to 45 ,then at operating temperatute it falls to 10 or below. When checking the compression I notised a lot of bleedoff on 1&2 , that is it took 4 to 5 more revolutions to get a full reading and I could hear the compression blowing by something, I can't tell where from . All the spark plugs were almost as white as new with a light tan color at the valve side.

 

Those reading are not exactly good. You want to those readings to be within 10% or so of each other (from highest to lowest). It sounds like you are losing your head gasket. You can lose it between 2 cylinders and not have any coolant leak. When I blew my head gasket I was running 125-135 psi on all my cylinders except 2 of them. The two bad ones were almost identical and were sitting at 20psi. It got so bad near the end that I could actually see exhaust coming out of the carb. You may not get the exhaust out of the carb symptom but the compression number say you have a leak between cylinders. If it were a valves you most likely would not have low number on 2 cylinders. Check out <a href="http://mark.legendz.com/4x3/update-emmisions.html">http://mark.legendz.com/4x3/update-emmisions.html</a> for a piacture of my head gasket when it went. Sorry for the bad news, but it is not that hard to fix. The hardest part is the r&r of the intake/exhaust manifold. I got the head cleaned up and a valve job done at a speed shop in town for about $200 (including replacing a couple of worn rocker studs).

Mark
mark@legendz.com
<a href="http://mark.legendz.com">http://mark.legendz.com</a>
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>Finally got hold of a compression check
>tool . These are the totals
>from front to rear , 70
>, 65 , 115 , 125
>, 134 , 115 . All
>readings taken with all plugs removed
>.Cant find an oil pressure tester
>as of yet , I can
>make a good guess that on
>warmup oil pressure is up to
>about 40 to 45 ,then at
>operating temperatute it falls to 10
>or below. When checking the compression
>I notised a lot of bleedoff
>on 1&2 , that is it
>took 4 to 5 more revolutions
>to get a full reading and
>I could hear the compression blowing
>by something, I can't tell where
>from . All the spark plugs
>were almost as white as new
>with a light tan color at
>the valve side.

 

well nod, if it sounds fine at idle and low power,but when you juice it gets noisy the problem is surley valvetrain related. the compression readings you got are not a sign of a blown head gasket but more like bad valve springs or the worst of all a bent valve or valves. check your valvetrain for bad or sticking valves and you should find your problem.
good luck
scott

 

I would normally agree that lost compression one cylinder would mean valve, rocker arm, push rod etc. But it is not exactly easy to get 2 bent or damaged valves at the same time. I would definately pull the valve cover and check the valves before you pull the head. If you had a van like I do, I would say pull the head anyway and then work on the vavles.. If all is fine you are only out time, and the cost of the head, intake/exhaust/valve cover gasket. If all is not find you have it out where you can work on it.

Mark

 

Thanks for all the helpful information.After the new year I am having this motor rebuilt,dont want to fix half of the problem only to have to pull the motor again to fix the bottom half. Thanks again for the diagnostic info,it helped with my decesion to build. Nod in Redding Calif.

 

Just finished a new motor install in My 4x4.I sent the motor to a reputable motor builder and got it back last week.After cleaning and painting all the related parts my Daughter and I installed the 300 hooked up all related components,prelubed the engine,then after a few revolutions the motor came to life .I did the motor & cam break in as per the builder and am still in the break in period. all the previous problems with the motor are gone and it runs perfect.Thanks to everyone for all your help, Merry Christmas and Happy New Year !!!!

 

I know it's a little late for this but it sounds like a problem I had with a 240 once. It turned out to be a blown head gasket between two adjacent cylinders, which is what it looks like from the compression test.

Trail Rider

 

Hey...i got a quickie....if the prob was valve related, would the engine have the potential to burn oil.....I have decked out my 300 with all the Clifford goodies i could find and now it goes through 4 qts of oil in 3 weeks. I do also have a ticking sound (and i just replaced the header and intake gasket so there is no leak) I dont think it is the rings...i just rebuilt the motor last year. And it ran fine for a year.....but i am willing to accept the fact if it is and rebuild again.....sigh....help if anyone can....

 

That sounds similar to a problem I had once. It was a 390 with lots of miles, but all of a sudden it started using lots of oil - a gallon in 100 miles. Nobody could seem to give me any idea of what it was. So I rebuilt another engine and dropped it in. That one ran great for about two years when all of a sudden in about 40 miles it dumped all the oil. The only common denominator was there was oil all down the driver's side of the engine and the firewall. The dipstick was also up about an inch. At the time I was enroute from Cal to Iowa. I refilled it and continued on. It never did it again. Later someone told me that on occasion all the rings on one cylinder will line up and the blowby pressure will cause the dipstick to get pushed up, and if you're driving a siphon action will occur on the top of the dipstick tube sucking all the oil out of the crankcase. I'm sure that the first engine probably had a groove in the cylinder wall holding the rings in place. I never did find out for sure though, but it sounds feasible. Just a thought.

Trail Rider