I'm building a 386 (4.155" bore/3.56" stroke) small block. The heads are brand new 230 CC Dart "Iron Eagles". We bought them from Speed-O-Motive with Manley 2.08"-1.60" valves only, since we already had new COMP springs, retainers, and locks. We did have SOM do a 3 angle valve job with the new valves.

Before the engine left the engine stand, we decided to go with a much larger Lunati cam (268-276 @ .050"-.646" lift solid roller).
This also neccessitated a spring swap, so we went with Vasco-Jet (H-11) springs from COMP.

The heads are already on the engine, so I pumped the cylinders with compressed air to hold the valves. Everything went fine until I got to the last cylinder (#7). I hooked the air hose up and I had considerably more leakage past the exhaust valve. When I got the spring off, I spun the valve in the head and then tried to air it up again....Same thing. I was hoping it just had a small piece of debris holding it open slightly, but no such luck.

I pulled the head to get a visual. The seat and valve face both look fine. No visible nicks or anything.

Could it be that this particular valve was just missed when the others were lapped? Should I look for anything else? Is it possible lapping will fix this? All the other 15 valves were fine...With very little leakage.

Thanks,
Frank

 

Put the valve and spring back into the head. Position the head so that the intake port is up. Fill that intake port with water or solvent. It will leak through any gap between the spring and the seat. Once you determine where the leak is, then you can decide on a course of action.

With "new" heads you shouldn't expect any flaws with them. I'm thinking that chamber may have a crack or the valve seat didn't seal.

 

On any set of heads there should be "0" leakage none,nada,zilch,in the valves...
A good way to check them AFTER hand lapping is to fill the ports with turpentine or alchol and leave them set for several hours.Then catch whatever your test fluid is and do the other side.If there is any wet spots in the combustion chamber,un spring those valves and relap them untill you have no wet spot's.Then make sure the valves are set RIGHT and they will last a long time. On a cold setting add .003 to lash to come out right when hot.

Do BOTH heads--I know it is a lot of work-- but better now than 1500 miles down the road,and you have a bunch of burnt valves.

 

If its leaking air, its going to leak fluid too.

What I'd do is get some dykem, dykem the seat and hit it with the lap. That way you can at least get a visual of the problem and go from there.

Keep us informed and good luck.

-Mindgame

 

Thanks for the replies. I appreciate the help. The first thing I'm going to try is lapping them.

Frank

 

its possible they used the valves like they were out of the box ?

i always red-dye and grind every new valve out of the box for the simple reason that not every one of them is perfectly true !

its also possible that even if the seats might have been cut with a Serdi cutter and Serdi machine , the exhaust seat could still be off somewhat enough to leak in rare cases .


lapping the valve will help and show up problem , but doing a quick careful grinding of exh seat and that exhaust valve will be better..then lap the valve after.

a valve will still lap ok even if concentricity is off .001+ due to valve guide clearance...so thats why actually very light grinding of both the seat and valve is preferred , then relap after.

http://www.maxracesoftware.com/ProAc...ND_Chamber.jpg

http://www.maxracesoftware.com/Dart_...t3_12_2002.jpg

http://www.maxracesoftware.com/BBC_7..._2_640x480.jpg

 

I like Larry's advice better.

You already have the head off so there's really nothing to it. If you hit it with the lap as mentioned before. Just do it for a second and take a glance at the witness mark left on the seat. If it cleans up completely then it's likely going to be fine. I still like what Larry said on regrinding the valve and seat, then relap. Very good idea.

By the way, those pics belong in an automotive **** library.

Nice work Max!

-Mindgame

 

I've noticed there are those on this forum, that hold the procedure of lapping in high regard, and believe it is done for some purpose. Does anyone here, that performs/subscribes, to lapping of valves/seats, also indicate ( for concentricity/TIR) the seats/valves after their grinding/cutting of same? Of those that lap valves/seats, what TIR do you hold, or consider permissible, (prior to lapping) in completed job? And last, what do you believe, is purpose/accomplishment, of the lapping procedure?

 

Arnie,

I don't think anyone's suggesting that a lap will correct poor concentricity. We all know that the machine work has to be there... that the guides have to be within tolerance, etc..

With the new seat grinding machines and interference angles (seat angle to valve face angle) the lapping procedure isn't necessary. Some will even suggest against it rather adamantly. Doesn't mean people aint still doing it. Hell, some of the fastest guys I know are still lapping their valves and they'd probably smack you over the head with an engine block if you told them, "You aint suppose to do that!".

Easy to lose track of things amidst technicalities.

-Mindgame

 

Hey MG, thanks for the comments. Here I'm striving for a 'spirited' discussion with some/any one, in the business, and I get a response from someone, that (by interpretation of his post, by some) agrees with me.

However, when I review this previous comment, I'm not too sure.

As a test, I've made 'job shop quality' seats look perrdy by lapping, but they were still .004" out of round. It's helpful, to take note, of the size of the lapping medium.

 

arnie,

I only mention it because I think that'd be a viable way to check and see if there is a problem. A visual "aid" if you will. I'm not suggesting it be used to correct the problem.

And I'm not doubting you could seal just about anything with enough lapping. I'd also suspect that it would wipe out alot of the seat geometry if the concentricity wasn't there.

Later.

-Mindgame

 

The heads are in ANOTHER machine shop getting a GOOD valve job done.
I had the head in question checked and found that the seat wasn't centered with the guide. Apparently it has something to do with the bronze guide installation.

Does Dart use bronze guides on all their heads?

Frank

 

Yep, as far as I can remember, I don't think I've ever seen a head from Dart that didn't have phos and mag bronze guides in it.

Happy to see you had them checked out and are getting the work done properly. Did they tell you how far out they were? Just curious.

-Mindgame

 

I was there when he took a cut on the seat that was leaking the worst. After a light cut, you could see where it touched more on one side than the other quite a bit.

Frank

 

Frank,

It pays to check your parts doesn't it?

I'm not a machinist but I do check everything I get from a machine shop cause they do make mistakes time and again. I'm just glad you found yours cause this could have had you scratching your head for a while. Not to mention.... a valve can't dissipate heat properly if it's not touching the seat all the way around. That and the lack of concentricity could have cost you alot of money via a broken valve!

Good luck with your project. Hope everything else goes smoothly.

-Mindgame