Pin holes in the head sealing surface..., Can I run as-is, or should they be welded up? Options

[jhadler]

Hey all,

The motor is going back together, and upon close inspection of the heads, there are some small pinholes along the sealing surface of the head. I'd like to drop the head gasket and lap the cylinder to the head, but will these holes be a problem?

Based on the measurements, the pinholes will be 0.016" outside of the ID of the jug, and as such, covered by the jug. But is that enough? Can I run this as-is? Lap the jugs to the heads, and run sans gasket? Should I run I gasket? Or should I have the holes welded up and re-flycut the heads?

There's all of about 40 minutes run time on these heads right now.

Thoughts? Experience?

Thanks!

-Josh2

[type47]

Are the literally holes all the way through or just casting errors like maybe a bubble was cast into the metal? If it's just a bubble, then I'd guess it's not a problem. Seems to me the thickness of the cylinder mating surface would cover the holes. I wonder if filling in the holes with JB weld would help. Cap'n? Jake?

[yeahmag]

You need to fix that. It's the sealing surface for the cylinders...

[HAM Inc]

Someone welded the ex stud boss that runs under the chamber and didn't get good penetration in that area. I can see the weld seam. The pits are porosity in the weld. If the head isn't prepped properly prior to welding that's the result.
The right way to fix it would be to pull the ex. seat, mill out the suspect weld and have a competent welder re-weld. Then machine for a new ex seat. I would run it as is before I would weld and not replace the exhaust seat. Welding that close to the ex seat is risky.

[yeahmag]

Would running a small (thin) copper sealing ring help?

[jhadler]

Someone welded the ex stud boss that runs under the chamber and didn't get good penetration in that area. I can see the weld seam. The pits are porosity in the weld. If the head isn't prepped properly prior to welding that's the result.
The right way to fix it would be to pull the ex. seat, mill out the suspect weld and have a competent welder re-weld. Then machine for a new ex seat. I would run it as is before I would weld and not replace the exhaust seat. Welding that close to the ex seat is risky.

Thanks!

Would you run with a gasket, or just lap the jug to the head and call it good?

Based on the measurements, the jug would fully cover the hole (it's just a pocket, and doesn't go anywhere).

-Josh2

[HAM Inc]

Would you run with a gasket

No gasket.

or just lap the jug to the head and call it good?

You can lap it, but I wouldn't call it good!
You probably won't suffer a catastrophic failure, but you may develop a head leak at some point. If the flycut is perfect and the case is perfectly decked then you stand a fighting chance. Otherwise...
What is your compression ratio?

[jhadler]

No gasket.

Okay. That was what I was hoping to do.

You can lap it, but I wouldn't call it good!

Good enough for a daily driver? Good enough for an autox car? Good enough for the occasional track day?

You probably won't suffer a catastrophic failure, but you may develop a head leak at some point.

Short term? Or long term? I'm not likely to be able to do yet another tear down after this build for quite some time.

If the flycut is perfect and the case is perfectly decked then you stand a fighting chance. Otherwise...
What is your compression ratio?

<gulp>. Well, I trust the guy who did the heads. And I believe they're done well. The case has not been decked recently.

CR. I haven't crunched all the numbers yet. But 96's on a 2.0L crank, and the heads have all measured out at 64cc's. I suspect it's gonna be at least a full point higher than stock.

If you think they'll manage well as is, I'll leave 'em alone. If not, I'll have them fixed. I don't think I can afford to have to do this all over again in a year or two...

JB Weld? (IMG:style_emoticons/default/biggrin.gif)

-Josh2

[HAM Inc]

If all of the work is otherwise good you'll probably get by. With a .040" deck ht and 64cc's you're looking at 8.2:1 compression. Keep your EGT's under 1250 (1200 is about right for longevity) and don't let it run lean.
DO NOT JB WELD IT! That will just make matters worse. The temps in that area of the head will run about whatever your EGT's are. JB Weld won't hold up.

[jhadler]

If all of the work is otherwise good you'll probably get by. With a .040" deck ht and 64cc's you're looking at 8.2:1 compression.

I think my deck height is a bit less than that. But I need to confirm that.

Keep your EGT's under 1250 (1200 is about right for longevity) and don't let it run lean.

Hmm. No EGT on the motor at this time. I have the VDO head temp sensor (under the spark plug style), will this give me any relevant info? And should I put it on the cylinder in question? Or leave it on #3?

DO NOT JB WELD IT! That will just make matters worse. The temps in that area of the head will run about whatever your EGT's are. JB Weld won't hold up.

I wasn't really thinking of it. I know that while JB weld is pretty neat stuff, it's not up to the task of a combustion chamber.

-Josh2

[Cap'n Krusty]

WTF is this obsession with JB Weld? NO, it won't work, not even for a few dozen miles. Fix it right. Fix the head, measure the cut and shim the barrels accordingly.

The Cap'n

[jhadler]

Easy Cap'n... My JBWeld comment was in jest...

Yeah, I figured that it was probably gonna need to be fixed properly. Sounds like the head will need to have the valve and the seat pulled, the pin-holes milled out, and then re-welded and fly cut. After all the work that went into these heads, I hate the idea of re-doing it all. But with all this work going into the motor, I'd hate to be throwing it all away and need to tear it down again later on...

I guess I'll talk to the guy who did the heads, see what he has to say.

-Josh2

[jhadler]

I spoke with the fellow who did the heads. He recommends a gasket, or copper fire ring, and doesn't think that it'll be a problem at that point.

He also suggested the following:

0.010 - 0.012" deck height per inch of bore. Which works out to 0.037 - 0.045 dech height.

additionally, he suggested 0.100 to 0.120 clearance to exhaust valve at TDC. (squished clay measurement).

Do these things sound good to you all? He's a good builder, and I have no reason to doubt his experience, but would like to hear opinions from the experienced engine builders here...

Thanks,

-Josh2

[jhadler]

(IMG:style_emoticons/default/icon_bump.gif)

Everything's going together now, but wanted to find out what others think about gaskets.

Should I run a gasket? If so, what kind? Most of what I know is that there's a standard copper gasket at 0.040 thickness. Is there an off-the-shelf gasket that would come thinner? Should I use that if I can find it? I don't want to make this car an overheating pig by going too high on compression, but would like to give the motor as much pep as I reasonably can.

Len? Cap'n?

Thanks!

-Josh2

[yeahmag]

Gaskets on the barrel side are for adjusting CR. You need to do your math and figure out where you are at vs. your target CR.

Copper gaskets are run by some between the barrel and the head. I've never done it, so can't say...

[Mark Henry]

Len gave you the answer...no gasket.

Would you run with a gasket

No gasket.

[VaccaRabite]

Just to be sure you are clear on this. The rings between the block and the cylinders are shims, NOT gaskets, and you need them to get your target CR.

The rings between the cylinders and the heads ARE gaskets. Running them or not is a source of debate, but I don't.

Zach

[jhadler]

I'm talking about head gaskets, not the barrel shims...

-Josh2

[ME733]

Pin Holes....the most reliable, and cost effictive way to solve your problem is to "fly cut " the head sealing to ( cylinder) surface...until you get a flat pinholess sealing surface....then...you can install the "stock" cylinder to head sealing ring,after a light lapping of the cylinder to be used......AND.....to really do this right consider duplicating this work to the other cylinder head....so everything is matched up..........THEN.....you can use cylinder barrell shimms of equal thickness under ALL the cylinders. consider this also ...the stock head seals will "CRUSH'' ,compress, when the head is torqued down....measure the before ...and after....crush....torquing.(gotta torque and remove and remove, measure and reinstall and retorque the heads.).....now the measurement of the head sealing ring will show how much LOSS in deck clearance occurs.(due to being crushed)......(you already installed a quesstomated,(measured) number of Barrell shimms.....and with the clay....you stragetically....previously...placed on the combustion chamber and piston tops.....at the smallest area of "squish"...you can now accurately measure the P/H...piston to head clearance.(deck-height).....My technigues over 35 years has been to keep everything in balance. and use the best parts available. piston to head clearance....bore diamenter and deck height "estimates" are just a wild ass quess....UNLESS....your engine builder has experience with the EXACT piston(make, design and weight)...and the connicting rods to be used.....Gotta consider the strech of everything at temp.and rpms to be used...Therefore consider using at LEAST .050ths inch as a minimum p/head clearance..the pistom material does matter and you did not say anything about them..a very minor loss in compression,by using a SAFE piston to head clearance is far far more cost effective for a street car/autocross...than the results of a LACK of Piston to head clearance. (IMG:style_emoticons/default/bye1.gif)

[Jake Raby]

No gaskets.. Adding another expansion factor to the equation isn't going to be favorable and at best it would be a band aid.

Its not right. No one knows how long it will last.. If you can se this visually what lurks beneath??

This post has been edited by Jake Raby: Jul 1 2009, 12:35 PM