Bad Compression?

**comongoose** · 02-21-2009

So as some of you may know I am currently in the process of putting an L26 bottom with an L67 top into my car. Right now I am a little past the mid-way point, as today I had got the valve train on and the lim torqued down, with the motor on a stand. Me and my buddy then decided to get a quick idea of the compression at this point. As he spun the crank, I put my finger over the spark plug holes to feel. The bottom end has 26k miles on it and the rings are mint. All the cylinders held pressure very well, except for the back two on the opposing heads. The head in the front was the worser of the two. I could hear a hissing sound coming out of the LIM as the crank compressed that back cylinder. The back cylinder on the other head was not as loud but I could also hear a little air escaping as well. I am guessing there is a problem with the intake valves on these two cylinders. I am on a budget with this car, and I need to know how bad this is? Do I need to tear it apart again and fix the heads or should I just rock the motor as is. Also does my half-ass test while on the engine stand have anything to do with it? When this is all done I want the car to be reliable, at the same time I am getting eager to finish and running out of money. Any input will be greatly appreciated. Thanks in advance.

TDCRacing · 02-21-2009

Well if there is FOR sure a hissing sound comming from somewhere other than the exhaust or intake then you need to take care of that. It is more than likley the LIM gaskets. Or possibly even the head gaskets.

**comongoose** · 02-21-2009

Well it sounds like it is coming out of the intake, is that alright?

**comongoose** · 02-21-2009

I used new head gaskets, I'm guessing I have to buy a whole new set if i want to redo the heads, even if I didn't put it in the car yet? Do you guys think I can get away with using LIM gasket again. It hasn't seen water yet.

**blueguy** · 02-22-2009

Originally Posted by comongoose

Well it sounds like it is coming out of the intake, is that alright?

No...think about that if the car was running...I highly doubt you would want everything pouring out of that gap you might have.

**comongoose** · 02-22-2009

ya thats what i figured. Im guessing its a valve so im going to take the heads back off and lap the valves. Does anyone know if i can reuse the LIM gasket?

**Sabrewings** · 02-22-2009

I don't see why not. Inspect the gaskets as they come out and see if they look roughed up. If not, they should be fine.

**comongoose** · 02-23-2009

Okay tonight I stepped backwards two steps and took the heads back off the motor. When looking at the valves of the "bad" cylinder on the head, they actually looked cleaner than some of the "good" cylinders. Is there a way to inspect the heads. I have never done head work before, except lapping valves. Should I lap the valves and reinstall or is there some good ways to detect whether there are other problems with the heads. Or should I just buy new valves and have the heads re-done. How much do you think that would run me. Thanks for all of your guys input thus far.

TDCRacing · 02-23-2009

I have a question. And it may be a stupid one but was the hissing noise possibly coming from the injector hole? Was it on the compression stroke that you heard the hissing sound?

So you're using l67 heads and l67 intake on a l26 bottom end?

You could do a leak down test but would have to buy the tool and do it while everything was assembled. A machine shop may be able to perform some kind of test if you bring them the heads but i'm not sure.

As far as the valve's being clean, That really does not say much.

I would get some lapping compound and lap the valves. If that does not work then it has to be gasket related.

**comongoose** · 02-23-2009

the noise was definitely coming from the LIM, but I also heard a little bit of mysterious crackling noise as well from who knows where. This was all during the compression stroke. I do have L67 intake and heads on the L26 block. I could get the leak-down tester from harbor freight for 35 bucks but I m not sure how to use it, where do you put the compressed air? Also just so you know I also had torqued the heads down in the wrong pattern, I accidently used the smaller v6 motor pattern. I don't know if this has anything to do with it or how specific the pattern is. I noticed on the top swap write up sticky they have a slightly different pattern that what is seen on autozone's repair manual write up as well. I might have also not have cleaned the block as well as I should. A buddy and I stood there for almost 2 hours scrapping it with a razor blade and got all the gasket off but the black underlay wouldn't come off. Maybe that is part of the problem. When I wanted to take the baked off gasket on my TB I used 1200 grit wet sand paper, is this safe on the block and heads as well? Should I look into a shop that will clean the bottom of my heads?
Now that I am no longer in a rush for this car, I think I might add some light performance as well. I was looking at getting modded 1.9 rocker arms and maybe springs. If I get larger valves from WBS can I lap them to the heads? Also will these do any performance for me if they are not ported? The valves look pretty haggard so I was thinking maybes new valves would be a good idea? I want to get this all right in one shot since its getting kind of expensive having to keep buying 60 gaskets.

TDCRacing · 02-23-2009

Originally Posted by comongoose

the noise was definitely coming from the LIM, but I also heard a little bit of mysterious crackling noise as well from who knows where. This was all during the compression stroke. I do have L67 intake and heads on the L26 block. I could get the leak-down tester from harbor freight for 35 bucks but I m not sure how to use it, where do you put the compressed air? Also just so you know I also had torqued the heads down in the wrong pattern, I accidently used the smaller v6 motor pattern. I don't know if this has anything to do with it or how specific the pattern is. I noticed on the top swap write up sticky they have a slightly different pattern that what is seen on autozone's repair manual write up as well. I might have also not have cleaned the block as well as I should. A buddy and I stood there for almost 2 hours scrapping it with a razor blade and got all the gasket off but the black underlay wouldn't come off. Maybe that is part of the problem. When I wanted to take the baked off gasket on my TB I used 1200 grit wet sand paper, is this safe on the block and heads as well? Should I look into a shop that will clean the bottom of my heads?
Now that I am no longer in a rush for this car, I think I might add some light performance as well. I was looking at getting modded 1.9 rocker arms and maybe springs. If I get larger valves from WBS can I lap them to the heads? Also will these do any performance for me if they are not ported? The valves look pretty haggard so I was thinking maybes new valves would be a good idea? I want to get this all right in one shot since its getting kind of expensive having to keep buying 60 gaskets.

I don't see how any gasket or the wrong TQ sequence could cause a leak when you were building up compression by turning the motor. Now maybe when it was running or turning at a higher speed. I mean something would have to be way off for it to loose compression when you were just turning it like that.

You can bring the heads to a machine sop and get the bottom of the heads resurfaced. They usually take like .010 off to ensure flatness.

You may as well get a good set of roller rockers for the price of the modded. I noticed ZZP had added a 50.00 deposit. Wich makes them almost the cost of some Yella terra roller rockers.

As for getting the gasket off i would use a wire brush on a drill and be real carefull around the cylinders.Make sure you clean everything EXTRA good.

You'll need to take it to the machine shop if you get bigger valves. And don't get the valves with the undercut stems. They have a reputation for breaking.

**Sabrewings** · 02-23-2009

Take it to a machine shop and have them inspect it. I had my heads fully rebuilt, cleaned, and inspected and the price wasn't too bad. The heads come back practically brand new. You may have a crack near one of the valve seats. These heads love to do that.

Originally Posted by TDCRacing

You may as well get a good set of roller rockers for the price of the modded. I noticed ZZP had added a 50.00 deposit. Wich makes them almost the cost of some Yella terra roller rockers.

True, but you get the core back when you send yours back in. Actually, I'm sending mine in ahead of time so I don't even have to worry about it. Nothing wrong with modified stockers, so why bother with something like RRs?

**comongoose** · 02-23-2009

Originally Posted by Sabrewings

Take it to a machine shop and have them inspect it. I had my heads fully rebuilt, cleaned, and inspected and the price wasn't too bad. The heads come back practically brand new. You may have a crack near one of the valve seats. These heads love to do that.

True, but you get the core back when you send yours back in. Actually, I'm sending mine in ahead of time so I don't even have to worry about it. Nothing wrong with modified stockers, so why bother with something like RRs?

Thats what i figured, I read their article on deflection and how RR help fight that, but still the amount of lift lost with those heavy springs still is not worth the extra 125 bucks to me. BTW I found a shop that will redo my heads for $198 for the set. Sounds like a good deal, what do you guys think?

**Sabrewings** · 02-23-2009

Mine would've been closer to about $170 if I didn't have a stuck exhaust stud. Still, the price you quoted I'd say is reasonable. You can see what I got for the money here:

http://www.grandprixforums.net/f18/r...ads-10753.html

**Shaunk** · 02-24-2009

Originally Posted by TDCRacing

I don't see how any gasket or the wrong TQ sequence could cause a leak when you were building up compression by turning the motor. Now maybe when it was running or turning at a higher speed. I mean something would have to be way off for it to loose compression when you were just turning it like that.

You can bring the heads to a machine sop and get the bottom of the heads resurfaced. They usually take like .010 off to ensure flatness.

You may as well get a good set of roller rockers for the price of the modded. I noticed ZZP had added a 50.00 deposit. Wich makes them almost the cost of some Yella terra roller rockers.

As for getting the gasket off i would use a wire brush on a drill and be real carefull around the cylinders.Make sure you clean everything EXTRA good.

You'll need to take it to the machine shop if you get bigger valves. And don't get the valves with the undercut stems. They have a reputation for breaking.

I'll say this before I post this. I worked at an automotive machine shop and still do some automotive machine work.

Do not use a wire wheel on a drill if you have ever surfaced a head you would know why. It creates all sorts of high and low areas. A better way is a single edge razor blade scraper. As far as the surfacing goes no good machine shop would ever go and just blindly remove .010. You remove only what you need to. I'm not picking on the poster buy qouting him I'm just correcting some mis information. Now there are a couple ways to see if the valve are sealing with the heads off the engine, you can use a vacuum pressure tester which I doubt you have but a machine shop will. The old stand by way that tons of home mechanics still use and works well is fill the ports in the heads with thinner and watch to see if it leaks out. Your old valves and seats may need reground which is something any machine shop should be able to do.

TDCRacing · 02-24-2009

Originally Posted by Shaunk

I'll say this before I post this. I worked at an automotive machine shop and still do some automotive machine work.

Do not use a wire wheel on a drill if you have ever surfaced a head you would know why. It creates all sorts of high and low areas. A better way is a single edge razor blade scraper. As far as the surfacing goes no good machine shop would ever go and just blindly remove .010. You remove only what you need to. I'm not picking on the poster buy qouting him I'm just correcting some mis information. Now there are a couple ways to see if the valve are sealing with the heads off the engine, you can use a vacuum pressure tester which I doubt you have but a machine shop will. The old stand by way that tons of home mechanics still use and works well is fill the ports in the heads with thinner and watch to see if it leaks out. Your old valves and seats may need reground which is something any machine shop should be able to do.

And i appreciate you correcting me. I gave the exapmle of .010 because that is what i hear most people getting taken off.

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