buying first bronco -need help with compression test.

[JuanGrande]

I am looking at buying my first Bronco and I need some help figuring out the compression test. I went and check out a '69 bronco today and I did a compression test (I am very new to all this - I do have a '64 convertible caddy that I work on a little but...I am not a mechanic) on the motor. I only tested 7 out of the 8 cylinders (my wife was little pissed to be there since it was approaching two hours) and the compression ranged from around 120-125 to 130-140. Is this low? I know that if any one or more cylinders is significantly lower than the rest, that this is a problem. I haven’t been able to find a set number that the compression should be at – I saw a previous post by a member saying his compression was around 170-180. Any advice would be greatly appreciated.<br><br>Oh, by the way, I tested the motor by driving the bronco around for about 15 minutes, let things cool down about 10 minutes, and then one by one, I pulled a spark plug and tested that cylinder. I hope that I did this correctly???<br><br><br><br>

 

[JMurray]

One of my manuals say 155 is prime, I dont think that matters a whole lot in this case, now if you were buying a Bronco with a rebuilt engine then that number would come into effect.
You do not want the difference between the highest reading & the lowest reading to be greater than 75%.
You have 140 as a high and 120 as a low, if your lowest was lower than 105 you would have a problem.
If the low pressures were rechecked & a squirt of engone oil in the piston raises the pressure, then rings are suspect, if oil does not increase pressure valves are suspect (easier to fix).
If two adjacent cyls are low could be head gasket if oil does not increase pressure.
I usually give the engine 7 turns, & make sure to keep consistant on the amount of turns.
Hope this helps
Jerry

 

[JuanGrande]

Thanks for the info. This helps greatly. I am trying to figure out if I buy this Bronco, if I will have to replace the engine right away. I figure that i will have lots of other repairs to do so not having to replace/rebuild the motor right off the bat will be helpful. I think that it is the original motor - so I may look into replacing the timing belt since I have heard that this is usually a weak point. Thanks again.

 

[74bronc]

Just FYI, I think you meant "timing chain" as the EB engine doesn't have a timing belt. And yes, it is a good idea to change it out if you don't know how old it is. DON'T replace it with a stock replacement as they will stretch within the first few hundred miles. Get a double roller chain. A good place to find one is www.summitracing.com<br><br>Good luck with your purchase.