View Full Version : Leakdown problems after valve job (long)

09-06-2004, 10:42 AM
Hey guys,

On a customer's car, I recently did a fresh rebuild on his S13 Silvia DET motor. Part of the rebuild of the head involved a 3 angle valve job, resurface, and polishing of the combustion chambers.

When I went to pick up the head, I noticed they had forgotten to polish the combustion chambers. So, they went in and polished them AFTER the valve job (valve seat work) was done.

Another note: I wanted to assemble the valve seals, springs, retainers, etc...myself. So, they gave me back the head with the valves in the head but not fully assembled with the above mentioned hardware.

The machine shop says they test all their heads to hold 30 inHg of vacuum before leaving their shop. Can they still accurately perform this test without the valve springs pulling up on the valves?

Now to my point: After assembling the motor, installing it into the car and putting about 15 miles on it to seat the rings, I did a compression and leakdown test.

Here were my results:

1. 100 psi, 66% leakdown, intake valves
2. 135 psi, 30% leakdown, intake & exhaust valves
3. 107 psi, 67% leakdown, intake & exhaust valves
4. 135 psi, 19% leakdown, intake & exhaust valves

I then removed the cams completely from the engine and retested with very similar results. This eliminated the cams and/or HLAs from the equation.

So, on all 4 cylinders, I am getting leakdown through the intake and exhaust valves.

Several machine shops have told me that the machining may have been slightly off and driving the car MIGHT help to finish seating the valve seats.

The shop that did the headwork told that they vacuum test all their heads and that I must have bent all 16 valves at some point. I really doubt I did this. I was apalled when the guy told me this, as if I was a 5 year trying to assemble an engine. He told me that no amount of running will "ever unbend the valves". "You're gonna have to pull the head and bring it back in," he said.

This is an 8.5:1 CR motor with JWT S3 cams. Vacuum gauge readings at idle, warmed up are 13 inHg, steady.

My only theory is that when they went back in an polished the combustion chambers, they might have gone astray a bit and affected the valve seats slightly.

My question is this: is it possible that in some circumstances, driving the car might help seat the valves a bit more or should they be perfectly seated right from the beginning and they will never get any better?

I would hate to have to pull the head again, considering my customer has a $200 GReddy metal headgasket in there. Any advice would be greatly appreciated. For now, I am going to put a few hundred miles on the motor, seat the rings, and restest later to see how things look.

Thanks a lot guys,
Jay Whitely
Tampa, FL

09-06-2004, 03:36 PM
do you know if they lapped the valves with coarse and fine lapping compound to further seating the valves better. if not, im sure it'll affect the leakdown test.

09-06-2004, 05:18 PM
I am not sure, but I really doubt it. Is this something that should have been done after they went back in polished the combustion chambers? I doubt they went in again and did this. They may have hand lapped the valve seats the first time around, but it is unlikely they did it again (nor vacuum tested again) after the polishing, since the polishing was a quick rush job just to get me out of their hair.

I am going to put about 1,000 miles on the motor and retest. If it still leaks down (at all) through the valves, I will pull the head and hand lap the valve seats myself.

question: Can you lap the valves with the valve seals in place or will the spinning motion of the valve stem "heat up" or damage the valve seal? I might just put new valve seals in (again) if I hand lap later.

Thanks a lot!

Jay Whitely
Tampa, FL
GTi-R powered 200SX

09-06-2004, 05:52 PM
how's the car running btw, with that sort of leakdown, im sure it'll run like [censored]. when i had three angle valve job done on my head, the machine shop didn't lap the valves, that's something extra. but if you are certain they did lapped the valves. then most likely they messed up the valve seats when polishing the combustion chambers. i guess you can eliminate the bent valves as your problem due to your leakdown result.

09-06-2004, 06:46 PM
Actually, the car runs great and you would never know there was a problem just by driving or listening to it run. I could give the car back to the customer and he would never know the difference. However, this is really bothering me because I like to do things right and I don't want him to lose all kinds of power or even burn an exhaust valve.

I have fixed broken timing belts on several Hondas that ended up having bent valves and they made "0" psi compression on those cylinders. Seeing as how I have close to normal compression, I think the valve seats are not that badly damaged.

I do not know if hand lapping was done to this head or not. I am not sure if it is a standard practice or not with this machine shop. I will have to call and ask them.

Here is my concern. I was thinking about having the customer take the from my shop and put a few hundred miles on it to seat the rings and get the engine broken in, etc...and then retest to see if things get better...if this is even possible.

However, with leakdown present in the exhaust valves, I am worried that he may burn a valve...sort of like tightening your valve lash too tight on a Honda. The valve never fully closes and the exhaust valve ends up getting really hot and shreds up....thus tearing his HKS GT3037 turbine wheel.

I may just bite the bullet and pull the head and have it vacuum tested and hand lapped. Oh well, what's another 10 hours out of my life to be sure nothing catastrophic happens?

Thanks man,
Jay Whitely

09-07-2004, 01:42 AM
well... in a perfect world, rebuilds that go awry would just fix themselves, but... unfortunately they dont. i've got a freshly rebuilt ka24e sitting in my garage and a junkyard engine in my car because theres something wrong and the hydro lash adjusters wont stay primed and keeps wearing out new ones, so... id say pull the head and fix the problem.

09-07-2004, 06:24 AM
I'm gonna go out on a limb here. Someone told me that I can reuse the GReddy metal head gasket. It has only 14 miles on it. Is that true? I would prefer to just spring for a new one unless this other guy is right.


09-07-2004, 08:11 AM
Lots of guys do...

I've heard of a few stories of "I reused my metal HG and it doesn't hold compression", but many more stories of good results.

- Brian

09-07-2004, 08:28 AM
honestly i would wait a bit more, since you rebuilt the entire engine, it's possible the leak down could be coming from the rings. What shop did your valve job?

09-07-2004, 09:05 AM
honestly i would wait a bit more, since you rebuilt the entire engine, it's possible the leak down could be coming from the rings. What shop did your valve job?

The great thing about a leakdown test as opposed to a compression test is you can tell where it's leaking from -- and he indicated that in his first post, right after the leakdown #'s.

I always thought you were supposed to put a set of old, junk valves into the head when doing chamber work specifically to avoid damage to the valve seats. Maybe they didn't have an extra set?


09-07-2004, 09:26 AM
My bad, missed that part http://forums.freshalloy.com/images/graemlins/smile.gif I've reused metal gaskets before without a problem, so if you are really in doubt, yank it out.

09-09-2004, 03:53 AM
Hey John,

There is definitely leakdown on the intake exhaust sides. I pulled the head today and did another leakdown test on the head on my workbench. I confirmed again that about 14 of 16 valve seats are leaking. I also vacuum tested each combustion chamber and none of them hold vacuum.

I am going to hand lap the valves and test again to see if this will cure the problem. I still think that all this resulted from the machine shop sanding and polishing the combustion chambers AFTER the valve job and seat work. either that or I bent 14 valves while I wasn't paying attention http://forums.freshalloy.com/images/graemlins/smile.gif

By the way, Clearwater Cylinder Head did the work. I would not recommend using them at all. NAPA does better work and has better customer service, etc...They did a rush job on this head and they have cost me a great deal of frustration and labor time that I will never recover http://forums.freshalloy.com/images/graemlins/frown.gif

I had my customer buy a new head gasket just for safety's sake. I don't want to pull the head a second time on this freshly rebuilt motor.

By the way, I used copper spray on the GReddy metal head gasket. I noticed that some of the copper wound up on and/or near some of the valve seats. Either this caused all these problems (doubtful) or it got sucked over into that area as a result of improper valve sealing during the compression and power strokes, etc...

Anyways, I don't want to use the spray if I don't have to. If it matter, I am using ARP head studs torqued to 80 lb-ft.