Valve Job Question, leak and light testing

[ahh911]

Hi Guys,
I sent away my heads to be re-worked by a Porsche centric machine shop in Alliston Ont several months ago. What is still bothering me is when I shine a flashlight up through the ports, the exhaust seat to valves show light (springs on). They also pass air bye when blowing air from my shop vac through the ports. I know the valves are ok, they are new and when I rotate them through the cylinder head, the gap always stays in the same location, also swapping valves has the same effect. A 0.001 inch feeler gauge still catches but doesn't pull as much in the same areas so clearly the gap is less than that. I took it to a local old school mopar type guy here and he pulled 18 inches of vacuum, if I recall.

Please, does this look reasonable? It may not be perfect but what do the experienced out there think? I'm ready to re-install but decided to ask.

Regards,
Phil

[Bigtoe32067]

They should seal better than that. I’d lap those valves in before I reinstalled the heads.
Tony

[ahh911]

Thanks Tony,
I bought some Permatex compound, but the grit looks too course (particles range from 120 to 220 and grinds down to 220, according to the package), locating 400Grit lapping compound is not easy here, for some unknown reason.
Phil

[Eagledriver]

Absolutely unacceptable. They must seal completely or they will burn in short order.

-Andy

[lvporschepilot]

Originally Posted by Eagledriver

Absolutely unacceptable. They must seal completely or they will burn in short order.

-Andy

Yup. A LOT of machine shops will cut new seats on the heads but won't reface the valves. I have seen this many times. It takes two minutes to reface the valve once the spring is off, unless they cut the seat incorrectly as well.

[Neil Harvey]

Phil,

Something is very odd here. There is no way you would be able to pull any vacuum with a gap of that size. Do not fit those heads as they are.

Give the heads back to whom ever did the work for you and ask them to do the work correctly.

If they ask why, ask them to vacuum test them in front of you. If they have no way of testing the sealing, they shouldn't be doing this work. Then you have to decide to give them another chance or ask for your $$$ back and go elsewhere.

The problem could be guides too, but regardless where the problem lies, its just poor poor workmanship. Tell tale to me is just how low they cut the seats. There is a limit, then the insert should be replaced.

Its not just about obtaining a good seal, its also about how much less the seat will flow and lower the engines performance. For example if you lost 10 CFM per seat, that's 60 CFM less in total and that will make a difference in how the engine performs. So you do not have to mess up the seat work to hurt the engines performance a lot. These heads suffer from flow when the seat is too low. They perform well when they are high. You can cheat this by cutting away the chamber some, but now you are increasing the chamber volume and decreasing the CR number. Also you will see the rocker adjuster further in, in the rocker arm.

This is typical of a lot of production machine shops. They work on the principle that the customer will not check their work. This is why you should use one of the well known Porsche machine shops that frequent this forum.

[boyt911sc]

A simple test to check if the valves are sealing is to pour some liquid over the cylinder dome and observe very closely for any sign of leak. Install an old spark plug and pour sufficient liquid like gasoline or rubbing alcohol to test for seepage.

There’s no way you could produce a vacuum with that gap. Send them back to the rebuilder. This is unacceptable workmanship. You are lucky you found this problem before assembling the engine.

Tony

[ahh911]

Hi Guys,
Thanks for your input. So, first thing is I ordered a "2 in 1 Brake Bleeder Kit & Handheld Vacuum Pump Tester, Vacuum Pressure Range: 0-30inHg, 0-760mmHg" from amazon, be here tomorrow. I can also use it to test decel and aux air valve. For 35$ bucks, it's about time. I want to see the vacuum it can hold for myself. As a note, the machine shop guys who checked the vacuum are a different company, local, but they didn't spend much time on it as they are not Porsche machine shop specialists like the one I sent this to and they knew they weren't going to get my business, just a friendly helping hand. I thought they said 18in and 20in for intake, but it was months ago.


Edit: Guys, to clarify, I have a 1thousand inch feeler gauge cut to a point. I removed the springs and feed it between the valves and seat, then press the valve down by hand a little, to see if the gap is less than 1thou, my thinest feeler. It is but in the areas where light shines through, the feeler is definitely encountering less resistance, so the gap is only gauranteed to be less than .001in. That's what I meant in my original post, should have been more clear. But again, the light and the bubble tests were with the springs on.
Phil

[trond]

I would NOT send them back to the same company. Heads are valuable and better go to someone else ! Don't let them touch your heads again. Forget about sunk cost

[Walt Fricke]

A seal is a seal. A leak is not a seal. Forget about feeler gauges, though, fine pointed or not. There is no plus or minus on a seal.

Since you think your valve grinding compound is too coarse (maybe someone here can tell you it is fine, though), use Prussian blue. Coat a seat, install valve, and rotate valve head round and round. Remove and look for anywhere it wasn't worn off. If any, seat not true.

Repeat with blue on valve. Same deal. If it isn't worn evenly, the valve wasn't ground true.

I made a plate I can bolt to the ports, with a gasket to seal it, and a tube in it to pump air in or suck it out, using the same tool you bought. Did I see photos of soap bubbles, showing how air passed the seated valve into the combustion chamber? You don't need any significant pressure to find a leak - just a small differential will blow bubbles. You could blow through a rubber or other tube, long enough to bend around so you could see the valve head while blowing. And there shouldn't be any at all with you just holding the valve head in place with a thumb, must less with the valve springs.

Seeing light is kind of huge.

I suspect some of us might like to know which shop did this. Trond wouldn't - he's in Norway. The guys like Neil don't care, as they do their own work. Others might.

On the other hand, it is appropriate to start with whoever did this. Discussion will give you some more insight into how they do business. Me, I can't imagine not lapping the valves in at least a little bit, just to see. Or at least using blueing to see where the contact is, and how wide. Plus doing a vacuum or pressure test before the work goes out the door.

I once bought some reconditioned EFI injectors from a shop which sells them, or reconditions yours. Then I wondered why my engine wouldn't start (first go around with EFI). Turns out they wouldn't open. Called the company. Oh, blast. My son must have forgotten the final step, which was to run some lubricant through each injector before shipping. By then I had purchased other (much more expensive) injectors, so he sent my money back without a fuss. I'd do business with him again. They did know what they were doing. I now know I should test them, though.

[Tom_in_NH]

If new valve seat was installed, it might not be parallel with the valve guide.

[Neil Harvey]

As a company owner, I would appreciate knowing if I did something wrong before the world found out. We all have to feed the family, our employees do the same. We all can make a mistake. Its about how we fix it that counts at this stage.

FYI, if a new insert was fitted the seat should be concentric to the guide as the guide should be used to center the pilot. If the guide is way out of spec and EX guides typically are, this could the cause. If the seats were ground (stones) or cut on a Sunnen seat and guide machine, for example, a tapered 'dead" pilot is used to locate the pilot. But once the seat is cut, the valve can "flop" around in a worn guide as the stems are straight. One of the reasons why I like "live" pilots.

You can fit the valve and push down on it and it should deflect enough to seal. This will give an idea the seat is not correct as well. If you decide to lap, ( good luck with that), it probably will take a while to get it right. Bounce the valve hard back on the seat and it give of a "tink" sound. If its like a "thud", its not sealed. You will never hit the seat as hard as the engine does when the engine is at RPM.

[manbridge 74]

That will not “ lap out.”

[ahh911]

Guys,
No new seats, guides all replaced and measure in spec using a split ball gauge. I also don't think lapping will help on some of these so I'm not trying yet. First I'll see how much vacuum they hold, then I'll try the liquid test but wouldn't vacuum be a better judge of this? I put rubbing alcohol around the valve last night without the springs in, just to see what happens, nothing came pouring out, that's for sure, but by the morning either it had evaporated or dripped in, which I think happened because I marked the seat with permanent marker and the alcohol disolves it as it runs across, so I could see where the leaks were, but I need to repeat this with the springs plus spark plugs in and more liquid, just as I did before they were sent out, and they did not leak for a whole week with degreaser in them before being sent out, but I don't think that means too much as the seat can be gummed up and prevent leakage anyway. I was just getting warmed up.

I'm kinda on my own with this, with your help maybe some sense will come of this.
Phil

[brighton911]

They are absolutely not acceptable. Sadly, I had the exact same issue a couple of years ago and the job was by a well regarded shop. When I called the shop owner out on it, he showed me they held vacuum. Indeed they did, that is with the pump on continuously, as soon as the pump was turned off, vacuum vanished. It's sort of like saying a boat doesn't leak if you have the bilge pump running all the time. They need to make it right without cutting the seats too deeply or other injustices. Good luck.

[dannobee]

You're "seeing the light" with the springs off? Or is the head assembled? Since I see the valve spring compressor in the pic, I'm assuming that you took the springs off.

Of course this isn't something that we like to see. The seat "concentricity" is less than ideal. Every cylinder head guy that I know checks concentricity on every valve seat for just this reason.

If the springs are off, it actually makes it look worse than it is. The Porsche factory spec for concentricity is 0.002". It could be that everything is within spec and you still see light with the spring off. And if your 0.001" feeler gauge drags, it could be within spec (although a seat concentricity gauge is the proper way to measure). Granted, ideally we all would want to see 0.0000" concentricity and no light even as we spin the valve around with the spring off. But if we're using the factory specs, it could be that the guy followed the Factory Workshop manual to the letter and ended up with this.

Now, in practice, what does this all mean? As Neil alluded to, once the engine lights off and the valve pounds the seat, it'll seal. You might find a slightly tighter valve lash on that cylinder the next time you check. If you just installed the spring and rechecked, the valve will deflect enough to make it seal. And if you're using vacuum to check the seal, it is, in effect, acting as a small spring to help it seal. Serdi's, IIRC, have a vacuum check built in, with a leakage indicator.

Now, how to fix it. Go back to the shop and see what they say. Give them a chance to fix it. All it would take (assuming the guide clearance was within spec), by your feeler gauge check and the amount of light, is a VERY light touch with the cutter or a fine stone. Then recheck the seat concentricity with the gauge.

FWIW, I've seen 911 heads with concentricity off a LOT more than that with leakdown and compression checks that were perfectly acceptable and only came in for oil leaks or oil consumption.

[ahh911]

Dannobee,

Thank you for the response. Springs are on in all the light and bubble test pictures. The springs are removed Only to clean the surfaces or rotate the valves or to try the feeler gauge. Funny thing is, with the spring on or off, it hardly makes a difference to the light test? (It's definitely less, but not by much)

I'm going to double check but awhile ago, I tried the original valves that were returned to me and checked the gap between valve and seat and if I recall .0025 inch roughly in the worst spots (to be re-confirmed) due to the old valves not being true. So I figured that it has to be better than before. I wonder if the old valves beat themselves into the seats and no longer rotated therebye achieving a good seal. Before I sent them out, I did the exact same bubble test and light test, Nothing came through except a little on cylinder 4, if I recall. Now it bubbles significantly where it didn't before on all cylinders, but only on the exhausts ports.

I wish I could send it back , but that's not an option and the transportation issues arose on the parts return (broken fins...) so I'll work with what's possible.

Phil

[Neil Harvey]

Originally Posted by ahh911

Dannobee,

Thank you for the response. Springs are on in all the light and bubble test pictures. The springs are removed Only to clean the surfaces or rotate the valves or to try the feeler gauge. Funny thing is, with the spring on or off, it hardly makes a difference to the light test? (It's definitely less, but not by much)

I'm going to double check but awhile ago, I tried the original valves that were returned to me and checked the gap between valve and seat and if I recall .0025 inch roughly in the worst spots (to be re-confirmed) due to the old valves not being true. So I figured that it has to be better than before. I wonder if the old valves beat themselves into the seats and no longer rotated therebye achieving a good seal. Before I sent them out, I did the exact same bubble test and light test, Nothing came through except a little on cylinder 4, if I recall. Now it bubbles significantly where it didn't before on all cylinders, but only on the exhausts ports.

I wish I could send it back , but that's not an option and the transportation issues arose on the parts return (broken fins...) so I'll work with what's possible.

Phil

Its easy to sit on the side lines and speculate what the problem is. However, they need to be inspected by someone who knows etc and has the ability to see the fault.
The problem will get discussed here but not fixed.

Be careful about fixing just the one head. If the seat needs a retouch, they all should get retouched to the same height.

If you do have to ship them again, go to H Depot or Lowes and buy a 17 gal plastic Tote. They cost approx $ 11.00. Go buy some cardboard boxes that the heads will fit in and pack those boxes in the plastic tote with some paper padding. Zip-ty the top and ship it. This will protect the heads. We tell our customers to do the same when shipping their cases.

Not to self promote PD, but often in cases like this we offer assistance to those that have gotten caught in issues like this due to no fault of theirs. We will help you out. It will not be free, I have to cover some time. But it will be at a huge discounted and reduced cost. You disassemble the heads completely and ship us all the parts. The more you do and less we have to do the less the discounted cost will be.

We will investigate the fault and tell you what we see. Hopefully its nothing to major, we would fix the sealing issue, vacuum test each valve, measure the retainer heights, and recheck the head heights. You need to tell us the camshaft used. We would test the springs and calculate the seat pressures. Send you a full spring and shimming report, what shims are required under each spring base. You then do the reassembly.

[ahh911]

Thanks Neil. In my case, the return packaging was created by the shop, it made it there just fine.

I'm going to study this some more with the armchair pro's first. We'll see how that goes, with all the pain in the ass shipping and delays I've had lately, let's first see if it's as bad as it might seem.

Vacuum checker is coming today. Con: people on rebuild forums have a consensus that vacuum checks are a placebo and mean little unless the defect is very large.

Liquid test, Con: first there is surface tension. There should be no leak, ideally. But should also check contact area.

Marker on valve, rotate the valve on seat to find contact area, done that will show images after I repeat.

Shining light test with spring on: As shown in picture, but can it be deceiving? Stuff is shiny, but most boards about rebuilds say if you see light, uh ohh.

Pressure into ports: Shop vac, what pressure? I'd need to insert a pressure gauge, but before I sent them out there were no leaks... but carbon would have sealed things up, so...

Neil, I'm in Ottawa Can, if you/Craig/Olllies or anyone lived within a 4 hour drive, man I'd be there in 5 hours 4 months ago. This is a specialists game, and in Canada the population is so low that it's tough to find the expertise.

Phil

[faapgar]

A lot of the time when the valve seats are touched up after new guides there can be a bit of chatter from the grinding method and you always need to lap them in with a valve grinding compound.I bought my last tube on Amazon.Like Walt says after lapping them in use a little Prussian Blue ink to check the seat width.You will feel better to to do this yourself.Fred