Hi Guys,

I own a 1968 F-100, that originally came with a 360 big block, which has later been replaced with a 302. Due to the fact that the truck has been owned by several people I don't know when the 302 was put in, nor do I know anything about where the 302 came from.

When I got it, the truck has a 3-speed manual tranny in it, which had worn clutch plates, and since it also has armstrong steering I decided to make my driving experience a little more comfortable by putting in an automatic tranny. This automatic tranny is C6 3-speed (one of those C6's, with integrated bellhouse for 302). It works like a charm, and yesterday morning I had them do a transmission flush after I drove with it for some months,in case of any dirt or impurities that may have been in there from not being used for quite some time before I put it in.

Anyway, to get back to the motor, I had some questions:

How can you effectively tell the level of wear an engine has undergone without taking it apart? I don't know that much about working on cars so I thought I put it out there for you guys to react to because I couldn't find much about it on the internet. I though that one way to tell if your rings and such are worn is to put in one of those pressure meters that you plug into each sparkplug hole? I did that one time on my other car, a 1980 Fairmont Futura, which has a straight 6 engine, and the results were that I had less compression on 2 out of 6 cylinders. If I remember correctly, 4 were at 140, while one was at 90 and another around 100. Is this the best way to tell if your engine is worn, or how worn it is?

I may be losing some compression because the gaskets on the motor, especially the valve cover gaskets, and around the distributor rod, are pretty much blown. So I will need to replace those. I do have another 302 block at the house, but that one still has to be put together and I don't have all the paraphernalia to put it together and especially to get it into the truck. So I am looking for ways to keep my current motor running as long as I can, but I don't know if it is really worth it, or if I should rather focus my time and energy on rebuilding one. So I would like to find out more about the condition of my current motor.

I appreciate all your help.


Oak

 

Doing a compression check will tell you how the rings are. If you have the same amount of compression between the cylinders add a little oil to each cylinder. The oil will temporarily seal the rings a bit more. If the PSI goes up then the rings are showing signs of wear. The same applies if you have some that are lower then the rest. If there is no change then the valves could be leaking. The head gaskets, valve seats and rings are the three things that will determine compression. Oil leaking out of other parts is not going to effect your compression. Another way to determine your engine wear is with a vacuum guage. http://www.centuryperformance.com/vacuum.asp This link shows what your looking at on the gauge and what it means.

Changing valve cover gaskets or any gasket for that matter is pretty straight foward as long as you have the basic tools. Valve cover gaksets wear out from heat cycling or old age. The oil you see around the base of the distributor may be from the valve cover, intake manifold, or the O-ring on the distributor base. I'd change out the valve cover gaskets first and clean the engine up as best as you can. Drive it around a little while and look for signs of oil leaking from the intake or O-ring.

The tools needed to rebuild an engine can be rented from a few different places. Check some of your local tool rental shops.

To determine the year of the engine you will find a few alpha-numberic codes cast on the the block near the starter, on the heads above the spark plug holes along the outside of the valve cover rails, and if you have the stock intake some where on that as well. Post those codes on here or google and it to narrow the engine down to which year it is. Then once you know what year it is youshould be able to find out what the compression was for that particular year.

 

Make sure you also post the actual DATE of cast codes shown here as that is important.



Design/engineering characters only tell what it was ORIGINALLY designed for not what year the actual part is.


as far as engine wear goes.. you need to inspect some parts first hand.

Rocker arms,push rods,

do a leak down test for each cylinder.

FTE has engine forums for these type topics as this is really just an engine specific related thread

 

I agree with Mil1ion about doing a leak-down test. By pressurizing the cylinder through the spark-plug hole, one cylinder at a time, you can find out both how much leakage you have, but also where it is going - rings, intake or exhaust valve, or into the water jacket. I use a piece of hose as a stethescope to listen to the crankcase & the manifolds, and, of course, bubbles in the water jacket are bad news.

I have not had this done for me professionally, so I don't know what it would cost. Probably more than a straight compression test, but you get more information out of it. Likewise I do not know where you could buy or rent the gage setup. What I can tell you is that I do mine with my screw-in compression gage with a few fittings to adapt to my shop air line. (Take out the valve in the spark-plug adaptor.) The engine will try to turn, so make sure each cylinder is at TDC on the compression stroke and cannot turn. (Parking brake tight & in top gear, with wheels blocked.)

I do a compression test first to see if the cylinders are even or not. Then if they are not, I can find out where the leak is with the leak-down test. The classic leak-down test setup was developed by Smokey Yunnick in the '60's or so. His setup pressurized the cylinder and then cut off the air. Then you observed the rate at which each cylinder leaks down, but I think the compression test gives you pretty much the same info.

 

Another way to do the leak-down test is at BDC with a rocker backed off, so that both the valves are closed. You only need to back off the valve that is partly open. Keep track of the number of turns & you can put things back the way they were easily. (FE's & Y-blocks will have to back off the rocker shaft bolts.)

 

Where exactly are the codes on the motor? I have a 302 in the '70 and would like to know what year it is.

 

What is that suppose to accomplish?
Most of not all the bore wear is at the top of the cylinder, below the point where the exhaust valve is opened wear is almost nonexistant.

To get a true reading you should use a differential compression checker only after the motors at full operating temperature.
Make a note of your reading at TDC, rotate crank until just before the exhaust valve opens and make a second note. These numbers should be within 6 psi of each other.
It is easy to make a differential tester, all you need is a valve, two accurate pressure gauges and a calibrated restriction orifice to the bore diameter of the motor tested.
For a bore less than 5" a .040" restriction .250" long with a 60 degree approach angle, greater than 5" bore a .060" restriction .250" long with a
60 degree approach.
Starting with 80 psi line pressure when testing.
With a standard compression tester a 20% difference between cylinders.
This is what I worked with per FAA Advisory Circular 43.13-1B paragraph 8-14b on specifications of differential compression testers.
If you use the same testing measures on an automotive engine you'll get accurate readings on engine condition.

 

If you are looking for which valve is leaking or anything that does not involve the rings, you can avoid having to block the crank at TDC. I suppose it might be of interest to compare TDC & BDC readings to see how much worse the leakage is at TDC. I just did a leak-down test while I had all the rockers off with an engine on the bench with no flywheel, so it would have been tough to lock it at TDC. If you do not lock it at TDC, it will go to BDC unless you have it EXACTLY staight up at TDC.

Thanks for keeping me "honest".

 

You can also use a vacuum gage for engine diagnostics - they are cheap and can reveal a surprising amount of stuff.

 

AND if you buy a vacuum gage DO NOT throw away the little chart that explains the "surprising amount of stuff".