Here are my compression numbers. Tell me what you think

[Anonymous]

I've got a 1968 mustang with a 200ci and a C4. I was planning on rebuilding the entire thing, but then i thought about only doing the head. So, i checked my compression. It seems a little low, but tell me what you guys think.

Also, i forgot to block the throttle open, and my battery was almost dead by the time i was done, so i didn't test again. But, I did remember to warm it up, so that helped out.

1- 125
2- 115
3- 115
4- 100
5- 75
6- 100

If you think i need to go it again with throttle open, just tell me. However, if you can give me pointers without, do that.

I'm planning on swapping the original head with a rebuilt and milled 80 head. Should i rebuild the bottom end at this time as well, or could i keep it as it is? I'm not going for a 9.5 to 1 compression, but something more like 8.7 to 1, so it runs well on pump gas.

I don't believe the engine is burning oil. I want to fix the engine for a reasonable amount, but I want to have it done right. I don't want to do the head now, and then 5000 miles down the road have to pull the head and rebuild the block. Thanks for your help
Any help would be greatly appreciated.

 

[StrangeRanger]

I'm assuming this was a "dry" test. repeat as a "wet" test, i.e. squirt about a teaspoonfull of oil into each spark plug hole before you test the cylinder. If your rings are bad #5 will show the same pressures as the other cylinders; If you've toasted a valve, #5 will remain low. If it's just a valve, you're going to fix it anyway.

 

[Anonymous]

Alrighty, i wet tested the cylinders. Here are the results:

1- 125
2- 120
3- 125
4- 140
5- 100
6- 125

Most of them look a little better. I guess that means i need to replace the rings?

What is the difference between moly rings and regular?

I know my timing is off if that makes a difference.

 

[wsa111]

If you are going to just hone the cylinder bores, I would just use cast rings which seat faster & are more compatible to previous worn cylinder walls.

If you plan to bore the block & install new pistons then I would use the moly rings, which take a little longer to break in but last much longer.
William

 

[Anonymous]

Well, im not sure if im going to bore the block out yet, so i'll plan on using cast for now. If my cylinder walls are not too scratched and gouged, can i just polish them up with a dremel tool fitted with some type of attachment? If so, what attachment would you use, and does anyone have any tips on doing this? Thanks

 

[mustang6]

There are basically two types of cylinder hones (that I am aware of).

The traditional kind looks like this:

http://www.toolgopher.com/browseproducts/Engine-Cylinder-Hone.HTML

but they work best on cylinders without a lot of taper (wear near the top of the bore)

The flex hones work best on cylinders with more taper but cost more:

http://www.boomerangracing.com/Engine Tools.html

 

[LaGrasta]

What should the result have shown if they were in acceptable order? I'm almost afraid to test mine.

 

[addo]

Well Anthony - when was the motor last worked on (I mean headwork, bore etc), and what level of knowledge would the operator likely have had?

You could have anything from 110 to 165 and not show any wear or loss, but it could also be on the lower end of that range and somewhat deteriorated.

 

[Anonymous]

Well, ive got the block apart. I was going to take it to the engine shop to get it bored, but it doesn't look too bad, and I figure that i would rather spend $200 than $800 for a complete rebuilding job. I was thinking about just replacing the rings, cleaning everything back up, and putting it all back together.

So, how difficult is it to replace rings? Let me remind you I have no previous experience with engines, and am mostly just learning. I have heard that i would need to remove the "lip" at the top of the cylinder bore, but dont know what tool I would need to use.

Also, I will replace the timing chain. Is there anything else you guys recommend changing or replacing while I have the engine apart?

 

[Lazy JW]

It isn't terribly difficult to rplace rings but I HIGHLY recommend that you find someone with experience to help you do it the first time. Those rings are VERY easy to break while putting them on, and proper technique is critical.
Joe

 

[mustang6]

A ridge reamer is the tool you need to cut the "lip" off to get the pistons out, but there is a rule of thumb that says if you have much of a lip/ridge at the top of the cylinder, then it needs to be bored.

BTW, a ridge reamer looks like this:

http://www.truckpartsproshop.com/ridge_reamer.html

 

[LaGrasta]

I'll have to test mine as I do have a compression tester. I don't know what the state of my engine and it's last rebuild is. I bought it and it's been serving me well for three years now. Starts and runs perfect. I suspect somewhat low numbers as there is blow-by when first starting it after it sits for a few days.