Compression Test Results after 13,000 miles on rebuilt 6bolt

[Trelisong]

This is 13,000 miles after rebuilding a 6bolt using 8.5:1 compression Ross Racing pistons. which means my standard compression should be 178 and service limit 133, So im assuming #2-4 look great right?

Here is the results, I noticed going from #1 to #4 on the dry test, the compression got higher as I went along.

I was also surprised and at the same time happy that my #1 didnt go up because that means it has to be the head right, and not the rings.

What does everyone think of these numbers, obviously #1 has a problem, but what about 2-4, I was surprised to see them go up in a wet test, does this mean there is a problem with the rings on 2-4 or no since they are close to the standard compression of 178

Dry:

#1: 138, #2: 164, #3: 175, #4: 179

Wet:

#1: 138, #2: 198, #3: 214, #4: 209

I just wanted to see what everyone has to say about this before I pull the head and take it into the shop.

I planned on seafoaming the car, but now I am wondering if I should wait until after I get the head looked at.

 

[bluegs03]

when you redid the shortblock did you do anything to the head? If not then i would point towards a bad valve in the #1 cylinder side, it might be burned or just not sealing properly

 

[50trimmed1g]

By looking at the pattern of the numbers, (increasing from one side to the other) is making me think a headgasket issue.

 

[Trelisong]

By looking at the pattern of the numbers, (increasing from one side to the other) is making me think a headgasket issue.

I was thinking the same thing, but number 1 is soooo much lower, is it possible that it could be just the headgasket, or possibly the head just needs to be re-torqued

but i dont know enough to know if that is possible or not with how low number 1 is, I just dont have enough first hand experience in the matter.

 

[Burnett03]

The wet test doesn't really tell much on our cars because our pistons are dished. So yes ofcourse the numbers go up when you add oil in the cylinder.

 

[Trelisong]

Also the headgasket that is on my car is the Cometic HP headgasket. I am not sure if this makes a difference or not, it is a metal headgasket and I was under the impression that these take a beating rather well, so unless I am needing to re-torque the head then the problem must be in the valve, number 1 is a large drop compared to the rest so I am thinking that it must be a valve.

I am just really hoping there is not any kind of surprises waiting, like completely destroyed piston/rings

 

[mach4g63t]

The wet test doesn't really tell much on our cars because our pistons are dished.

That makes no sense at all. Displacement is displacement. You add oil to a 'flat piston', that also has properly sealing rings, and it's going to go up. The problem here is that he added oil, or whatever, to the 138 piston and it didn't go up. If the number had increased, he could probably almost bet money that the added oil was causing the rings to seal in the cylinder and increasing compression, thus concluding bad piston rings.

Pull the head and have the valves looked at.

 

[KelTsi90]

When I rebuilt my engine this July I took compression and it was 160, 175,175,178. I have Cometic HG and ARP studs. When I gave it the break-in, I retorqued the studs and it gave 180 all across.

 

[crimsondragon]

The fact that compression remained the same on both dry and wet test on #1 means it's pointing to the head.

 

[illeffekt vr-4]

Did you do a compression test right after building the motor? If so, what were the numbers?

 

[t25fury]

That makes no sense at all. Displacement is displacement. You add oil to a 'flat piston', that also has properly sealing rings, and it's going to go up. The problem here is that he added oil, or whatever, to the 138 piston and it didn't go up. If the number had increased, he could probably almost bet money that the added oil was causing the rings to seal in the cylinder and increasing compression, thus concluding bad piston rings.

Pull the head and have the valves looked at.

Burnett03 made perfect sense, if the piston is dished, oil can collect inside the bowl of the pistion, there by decreasing displacement and increasing compression,although mach4g63t,your correct,if the wet test doesnt seal the rings to pass the 138 mark then no amount of oil will.

 

[mach4g63t]

I think I understand what he was saying now. By 'setting in the dish', you mean actually pooling up in the dish and never making it over the edges of the pistons to actually seal the rings, or attempt to. That's my bad!

 

[Trelisong]

Later today I am going to try to re-torque the head, and recheck results, I am really doubting this could be it, but who knows I guess?

If it definitely cannot be the headgasket then I would not re-torque it because I plan on reusing this headgasket, it cost over $100 which I cant afford right now.

 

[Trelisong]

Did you do a compression test right after building the motor? If so, what were the numbers?

No, I did not unfortunately.

when you redid the shortblock did you do anything to the head? If not then i would point towards a bad valve in the #1 cylinder side, it might be burned or just not sealing properly

Yes the head was also completely reworked, all valves were replaced and seated.

 

[BoredDSM]

Did you resurface the head? Did you clean the surface of the head or block with a scotch bright pad or any abrasive material? Did you torque it to the right specs? Did you re-torque after break in? How did you break it in?

 

[Trelisong]

Did you resurface the head? Did you clean the surface of the head or block with a scotch bright pad or any abrasive material? Did you torque it to the right specs? Did you re-torque after break in? How did you break it in?

Both the head and block were resurfaced by the machine shop that bored out the block 20 over for the new pistons. I did not clean the surface of the head or block, but it was shinny and clean when I got them back from the machine shop. I did torque to the right specs, but I never did do a re-torque.

I pretty much followed this site for the break-in: Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power