Headgasket cause low compression??

1gcrazy · May 29, 2012

So I bought a car a few weeks ago and it supposedly had a good motor that came out of a running car. The guy pulled the head off and since the gasket only had about 5000 miles on it, he reused it.
Well during my diagnosis I found the dumbass forgot to put the injector ignitor on the car during his wire tuck. Either that or he pulled it off to ensure it wouldn't start so I wouldn't realize the compression sucked.
After ensuring spark, fuel and air; I checked compression, only to find out it was very low.
1234:5,60,60,45
Now, I asked him about the head gasket and he said he reused it. He also promised up and down the motor ran prior to him pulling it out of the other car and pulling the head. Sooo, I'm going to pull the head off and at minimum check the valves, check the head for flatness and replace the head gasket. I'm also going to pour oil in each of the cylinders overnight to check if the rings are showing excessive wear.

My question is:
Has anyone ever heard of a reused head gasket causing such low compression??
It makes sense since the two outer cylinders are the lower of the 4. After hearing he reused the gasket, i'm doubting his methods.
He also couldn't remember if the gasket was MLS or composite which makes a huge difference to me.
Also, he wasn't exactly sure the ft.lbs he torqued the head to... I didn't put oil in the cylinders because of the dish in the pistons. I thought about channeling wd40 to the outer edge of each piston with the straw they come with hoping that would help but regardless I have to take the head off anyway. Just don't want to miss any diagnostic opportunities while the head is still on.

Thoughts? Tawk amongst yaselves...

issac712 · May 29, 2012

I'd say your best bet is to pull the head, and find out if the head is even warped, or if any valves have been bent. I'd replace your valve seals while your at it.
I dont know how to check for piston ring damage, but I would pull the oil pan and see if everything down their has any problems.

Jmonet1620 · May 29, 2012

If he reused the head gasket and your compression is that low its time to pull the head back off. Send the head to the machine shop to be cleaned and inspected. I wouldn't trust this guys word at all. He sounds like a total moron. Make sure you get a new head gasket and some arp head bolts. The oem composite gasket and arp head studs has been proven to hold 30psi. Also while everything is apart it would be the perfect time to replace the timing belt, tensioner and water pump.

issac712 · May 29, 2012

Jmonet1620 said:
If he reused the head gasket and your compression is that low its time to pull the head back off. Send the head to the machine shop to be cleaned and inspected. I wouldn't trust this guys word at all. He sounds like a total moron. Make sure you get a new head gasket and some arp head bolts. The oem composite gasket and arp head studs has been proven to hold 30psi. Also while everything is apart it would be the perfect time to replace the timing belt, tensioner and water pump.

depending on how many miles is on the engine,maybe new timing pulleys too, also if the b/s belt is still there, I would replace those pulleys/sprockets to prevent any b/s problems.
Agree with quote on everything he mentioned.

gdmbat85 · May 29, 2012

Are you sure you're doing the compression test correctly? You need to let the engine complete at least 4 full revolutions per cyl. test. Also, it wouldn't hurt to do a leak down test while you have it together still.

Another note, a composite headgasket can not be reused. It falls apart when being separated.

issac712 · May 29, 2012

When I do compression tests, I don't stop cranking till the needle on the gauge stops moving. Also make sure your battery is fully charged and that you have a battery charger, why? Because the more you turn your motor over, your lossing a good amount of power, which will give u low compression numbers.

1gcrazy · May 30, 2012

Yeah, I KNOW the timing components are new. He couldn't tell me if it was composite or not and I failed to look to see if I could tell while it was sandwiched in there.

I am doing the compression test correctly. I doubt doing it wrong would yeild a ~90% spread. Either way, I'll try to get a look at the gasket. If it's composite, i'll just replace it and check the head myself. Nothing a machine shop can do that I can't. A leakdown test isn't easily feasible, i'll just pull the head try and look for scoring on the ringlands and replace the gasket. If I need to i'll pull the pan and replace the rings/pistons and do a quick deglaze.

No one chimed in on having the same issue. Has anyone ever actually had this happen? Or at least something close due to the HG?

gdmbat85 · May 30, 2012

Losing compression due to a headgasket? That's the entire purpose of the headgasket, so a bad one will obviously cause this issue. It's like asking if anyone has ever had a car not start because of a dead battery.

1gcrazy · May 30, 2012

Alright George. Has anyone had low compression in this RANGE from REUSING a head gasket. Low compression is obviously very subjective. Mine is VERY low.

gdmbat85 · May 30, 2012

They will range over the entire compression range. Yes a bad gasket will give you compression numbers as low as 0psi. It's actually more common to get lower numbers than higher numbers. I don't understand what you're really trying to get at with your questions. If it's a composite gasket and half the gasket is missing, you basically have a 1.5mm gap between the head and block. Obviously you won't get any compression. Reusing a gasket doesn't make the situation any different. Also, it being new or reused isn't going to have ANY indication of what to expect. People have reused MLS's and gotten perfect compression, people have used brand new ones and gotten like 45psi.

sting · May 31, 2012

Used gaskets can work - IF - you have perfect surfaces. Last one I reused was on a Sunday night putting my 348 Chevy back together so I could get to work on Monday... But if you went to all the work the better question might be -- WHY?

Head deck surfacing is EZ to have a good shop correctly prepare the head. Its more of a drama getting the block right. Scrape the block with a wide blunt tool to remove most of the crud - Then purchase a 180 grit wet stone about 6 inches by 2, and use it on the block deck with mineral sprites for lubricant. This will allow you to see if the deck is straight and if the any sport are raised - such as around a bolt hole where the threads may be beginning to pull. Also check around the bores with this - maybe the last "YUTZ" used a power tool to clean the block and rolled the edges off? If yes - even a new gasket will fail. It depends.

Kind Regards
Sting

lilredeclipse · May 31, 2012

1gcrazy said:
Alright George. Has anyone had low compression in this RANGE from REUSING a head gasket. Low compression is obviously very subjective. Mine is VERY low.

To simply answer your question. If everything was ok with the motor and I had to pull the head off for a dumb reason ( IE: non magnetic bolt falling in the cylinder.) I still had good compression if not the same compression. This was using a MLS gasket.

Every time I have pulled off a composite gasket it has left gasket behind and was not usable.

Also I have reused a MLS gasket 2 or 3 times before.

1gcrazy · Jun 1, 2012

Thanks guys.
Where can you find such a large wetstone?
SBC are pretty much bullet proof so all of their statistical references are null!

I've done a lot of reading and just tonight I did verify that the current gasket on the car is a felpro composite gasket. I hear that MLS's are able to be reused due to the nature of just being sandwiched steel.

I'll be pulling the head off tomorrow and replacing with another felpro composite, checking the head for obvious damage and checking the rings and cylinders.
I'll update once I get results.

sting · Jun 1, 2012

1gcrazy said:
Thanks guys.
Where can you find such a large wetstone?
I'll update once I get results.

Search KNIFE SHARPENING HONING WET STONE on e bay for one - check at the hardware store in town - or a gun / knife shop

It will last you a life time if you take care of it so just think of all the head gaskets you can look forward to changing LOL

1gcrazy · Jun 1, 2012

I swear. I do headgaskets for fun sometimes... I've probably done over 40 of them. But then again, i've owned over 30... Could do it in my sleep.

Headgasket cause low compression??

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