Valve stem seals and clearance

[Phoenix-MN]

Newbie here I've been lurking for a long time reading this forum for all of it's great info. I'm building a resto-mod with a 3.8 V6 NA (Turbo's little brother) I finally finished building it and fire it up last weekend with mixed results. I thought I had done all my homework and had the valve train all worked out. Lunatti Cam, Harland Sharp roller rockers on cast iron heads.

No issues with valve clearance but on startup and the first few minutes of running I had valve/lifter noise on cyln #3. After a few more minutes noise almost went away and was barely noticable. At that point I thought the valves just need adjusting. After letting it cool down I took off the valve cover and checked the adjustment and everything was ok. Then I found a small soft piece of blue plastic laying in the head. Scatched my head for a while trying to think what it was and finally determined that it was part of the valve stem seal. I used a miiror and light and can see that it is from the #3 intake stem. So I failed my homework assignment! The combination of the higher lift cam and 1.65 rockers pushed the spring retainer down on the end of the seal and smashed it good.

So here's my questions:
Since this only happened on one valve could the guide or seal been installed wrong? Could anything else been damaged? I assume I will need to take the head off to replace the seal so what else can I check while I'm in there. Is this a common problem? (I searched for this but didn't find anything)

Here's my V6 installed in the car.
phoenixhobbies-dot-com/html/prorgress_2008.html]Prorgress 2008


Thanks
Paul

 

[ek02]

If you did not machine the valve guides for the seals, you don't have enough retainer to seal clearance with any cam over .420 lift at the valve. If the retainer hit the seal, then it has to be very close to the top of the stock guides. The soultion is to remove the heads and have the guides machined. But that poses another problem. You can't run seals on the exhaust guides with stock exhaust valves because they have a step in the valve stem that will tear up the seal as soon as the valve opens. You need an aftermarket valve with a solid stem. NAPA and others can supply them, or try TA Performance. Don't try to machine the exhaust guides down and run them with no seals, it will smoke out the tailpipe every time you stop and idle. Been there and done that. A Mickey Mouse solution if the retaners are barely touching the seals is to machine the under side of the retainers for clearance. You need .060 clearance from the retainer to the seal at full lift to be right. Or, maybe you lucked out and the seal was not installed all the way. You can put air in the cylinder and pull the spring to replace the seal with a valve spring compressor.

 

[turbodave231]

You'll need to cut the guides down and install new seals. This can be done without disturbing the valve job, but the heads will need to come off and be disassembled.

DR

 

[turbofabricator]

I agree with both posts.

 

[Phoenix-MN]

Thanks guys,
I found an old book on V-6 Performance and it mentioned that the exhaust doesn't use a seal is that a mis-print?

I'll be pulling the heads and dropping them off to the shop to be checked out/disassebled/measured to clearances.

Paul

 

[Rodney87GN]

Thanks guys,
I found an old book on V-6 Performance and it mentioned that the exhaust doesn't use a seal is that a mis-print?

That is correct from the factory...which is why you must cut down the guides if you want to use valve seals on the exhaust side.

 

[jhanson1750]

Just picked mine up from the machine shop on Wendsday for this very prob. Pull the heads and have the valve boss machined. Then pony up and get the valves that you need to run seals on the exhaust side and be done with it. My heads have new(ish) valves without the step but to much lift still ate the seals. Jon Hanson

 

[turbofabricator]

If you cut the exhaust guides down for seals, you MUST also replace the factory exhaust valves with an aftermarket stainless valve or a factory TTA exhaust valve. The factory exhaust valves have a groove in the stem that acts like an oil pump, and a seal will NOT seal against this groove.......PERIOD!

 

[Walt03]

How Much To Cut The Exhaust?

If .420 lift on the exhaust side will work with unmachined guides and stock exhaust seals, how much do I need to machine on the exhaust side for a 206/206 roller -.496 lift, with stock rockers(1.55 ratio). .080??

If 1.65 rockers are used, is the lift about .520 and would the exhaust guide need to be machined about .100??
Will this allow to have the .060 clearance at full lift?

Would the same measurements be for the intake?
What kind of seals do you use? Viton?

I don't plan to use the stock vales for intake or wxhaust.

Thanks

 

[ek02]

What I do to determine the amount to cut the guides, is put an intake valve in the head with a seal on it. Install the retainer to be used, and measure the distance from the retainer to the seal with an inside michrometer or a dial caliper. Take the valve lift and add .060, then subtract your measurement from that total and cut the guides that amount. Example: .500 lift+.060=0.560. The measurement from seal to retainer =.400. .560-.400=.160. Cut.160 from the guide. Cut the exhaust the same amount. I use Viton seals. I have tried Teflon seals and Viton with Teflon inserts. For the street, I like Viton the best. They last a long time.

 

[Phoenix-MN]

Spring update...
Pulled the heads off and took off the #3 exaust spring and look what I found Stepped valve stem with a seal! (stupid machine shop). I guess I'm going to look for a better shop that knows these engines.

 

[charlief1]

ek02 has a good method but I will add that I usually cut them to the nub so I can upgrade the cam at a later date. This way you don't have to take the head off if you need more clearance.

 

[turbofabricator]

Replace the valves with stainless aftermarket valves. Then have the machine shop cut the guides for positive seals and proper retainer to seal clearance. They NEED to know the cam and rocker specs to do it right. They may haave assumed that you were running near stock lift. They also need some "schooling" on the stepped vavle stem issue, too. Probably never seen them before on any small block Chevy.

 

[Phoenix-MN]

Well, I took the rest of the springs off and all 6 exhaust seals were destroyed the same. I took a few measurements and found that the guides have to be cut a lot. My cam exaust lift with 1.6 rockers is .512" add .060" and we have .572" I measured the retainer to seal distance and it's only .358" so .572-.358 = .214" to cut. The intakes were a little better and only need to be cut .103" (they did not get as beat-up). After taking the heads apart I think the shop pulled a fast one. The first thing I noticed is that the guides looked to have bee knurled instead of being replace as I had asked. Also, they were to do a 3 angle valve grind and this looks it was not done.



It goes to say, If you want it done right check and do it yourself.

 

[dr_frankenstein]

Well, I took the rest of the springs off and all 6 exhaust seals were destroyed the same. I took a few measurements and found that the guides have to be cut a lot. My cam exaust lift with 1.6 rockers is .512" add .060" and we have .572" I measured the retainer to seal distance and it's only .358" so .572-.358 = .214" to cut. The intakes were a little better and only need to be cut .103" (they did not get as beat-up). After taking the heads apart I think the shop pulled a fast one. The first thing I noticed is that the guides looked to have bee knurled instead of being replace as I had asked. Also, they were to do a 3 angle valve grind and this looks it was not done.



It goes to say, If you want it done right check and do it yourself.

I think thats a good sign of time to go to a new shop. money aint free to toss on crappy work.

A.j.

 

[Turbo1dr]

It goes to say, If you want it done right check and do it yourself.

I'm a FIRM believer in that statment! I hate letting other people do the work for me all because I don't have the necessary equipment to do it myself.

 

[87GN_70GS]

Not true. If you cut the guide down so that it is shorter, like I did on mine, you will be able to run the seal on the area of the stem where it is not undercut. This will work provided the lift is stock or reasonable. If you have super high lift such that it now moves the undercut area down to the seal at full lift, then it will not work.

If you cut the exhaust guides down for seals, you MUST also replace the factory exhaust valves with an aftermarket stainless valve or a factory TTA exhaust valve. The factory exhaust valves have a groove in the stem that acts like an oil pump, and a seal will NOT seal against this groove.......PERIOD!

 

[charlief1]

To solve some of the aggrivation I decided to measure the clearance between the bottom of the keeper (ex) and the top of the guide. It measured out to .4885 with a set of Mitutoyo digital calipers.That means you have .0165 clearance with the STOCK set up and that's just a little close for me. Cutting the guide is the best thing to make sure you don't go bang with the keeper.

 

[86GN-862+2]

I know this has probably been asked. What if you just need .015 of clearance for example? I thought maybe cutting the bottom of the spring retainer would be cheaper and NO NEED to remove heads. I thought of this as an option years ago when I was building a 400sbc which never got put together.:redface: I got the clearance and cost about $50 to have all the retainers cut. From what I saw, the integrity of the retainer is retained. No pun intended. Just a thought.

 

[ThikStik]

That what happened to me, funny thing car didnt use much oil. Anyway, took it back to them after schooling them, and he said he could cut guide down to work. I said new non stepped valve only....per Turbofab's input. Anyway, they sat on heads a year. So now i took it to some other fools and told them to grind valves and not mill heads and to call me on what valve they found. They put in SBI valves which will be an experiment i guess. And the valve heights are all over the place. Good luck