Leak Down Test Shows Leaky Valves-Could it be corroded seats?

I fired the car up today after it sat all winter in the garage. I warmed it up good and decided to do a leak down test to see how things were doing. It sounded good when running but my intake and exhaust valves seem to be leaking. I have air flowing thru the carb and headers with both valves closed. Could the seats have corroded over the winter? I turn the motor over by hand every couple of weeks with a ratchet but I didn't back the rockers off. Is my only option to pull the heads and inspect the seats? Is there any chance running it some more would clean them up? I can't say that I ever noticed this problem before unless I just didn't know it.

Even guys running gas can benefit from "fogging" the engine down after the race. The seats will damn sure rust up.

tap the valve stem with a plastic hammer to see if bouncing the valve close helps. how much is it what is the %. leave pressure in the cyl. when tapping the valves
dragweek quickest street rod
2009 201

It was leaking bad enough that the secondary gauge was only coming up around 15 psi at 75 psi inlet pressure.

that is very low did you have hyd. cam they will float the valve and hammer the seat and valve
dragweek quickest street rod
2009 2010

No its a solid roller. I'm thinking I better pull it a part and take a look.

512Fairlane wrote:No its a solid roller. I'm thinking I better pull it a part and take a look.

Thats the best

this is why i have my guys back the rockers off when sitting

Every cyl. has this condition?

I only had time to check two. The #1 and #4. With my shock towers I can't check the center two cylinders very easily.

I'm commenting on this because I also have P-51's. After running them for 2 years, I developed some compression coming back up thru my carb last fall. Not a lot, but just a slight bit of noise noticable at idle. I decided to pull it and do an overhaul before xmas. The machine shop said ALL of the intake valves were leaking slightly...none would hold vacuum. It turns out each was not sealing right by where the head stud is close to the intake valve edge. I called Kaase about it and the gentleman told me this was not uncommon on a new set to do this, He said given the large intake valves, thin stems, and layout of the BBF's 10 big head bolts it all added to the issue. I had mine skimmed when reassembled and retested after they were torqued down. All is good now. Same combo right down to the carb jets. I upped the compression 1 point only. I picked up .3 in the quarter right off the trailer from it's best last year.

Hmmm. That's interesting. I wish I would have leaked it down last fall so I would know where it was at before it sat. I have 125 passes on this motor. I replaced all the valves after the first 37 passes after shearing the cam pin and bending all the intakes. The seats looked good at that point so I just lapped the valves and put it back together. I suspected it might be corrosion because I was too lazy this year to back off the rockers but I did the same thing last year and didn't have any issues. It ran fine last October at the last race and it really didn't sound bad yesterday but I was only idling for the most part. Glad we decided to do the leak down. I was planning on pulling the motor out anyway because we are putting Mustang struts on the front end and we have to remove the motor to trim the shock towers back some more. I was going to look things over inside the motor but the valves weren't my biggest concern. Guess its time to freshen it up. Might be time for some of Charlie Evan's handywork on these heads.

I just put mine up aftyer a race, I do run alky but have a gas primer plus i BUILT SO I RUN IT ON RACE GAS BEFORE LOADING UP.........GET THE WATER GOOD AND HOT f in caps lock, i aint retypin that shit lol.

anyhoo, after I shut it down the vc filler and vac pump line come off so any moisture can escape. After I unload it the plugs come out and some spray lube go in the cyls, spin it over a bit, pull inj lines and blow out the barrel valve and lines, then blow some spray lube through it. plugs back in, stick some nerf balls in the collectors.

Every week I spin it over and make sure the same springs are not compressed. Winter time back the valves off.

Car is stored in a climate controlled shop so i dont get the humidity in there all the time. Car also goes up on jack stands.

Yeah after we get the struts on this thing and cut the shock towers back more I hope it will be a little easier to work on. Right now it takes about an hour to change the plugs and installing the headers is a good 4-5 hour job with a lot of cussing involved. Routine maintenance should be less of a hassle hopefully although after 4th horseman's post I'm wondering if it might be something other than corrosion.

512Fairlane wrote:Yeah after we get the struts on this thing and cut the shock towers back more I hope it will be a little easier to work on. Right now it takes about an hour to change the plugs and installing the headers is a good 4-5 hour job with a lot of cussing involved. Routine maintenance should be less of a hassle hopefully although after 4th horseman's post I'm wondering if it might be something other than corrosion.

Im with ya on that Mike!...headers are a pain in the A! How is the strut ordeal going?

[/quote]Im with ya on that Mike!...headers are a pain in the A! How is the strut ordeal going?[/quote]

Well I actually was taking the car out to my Dad's shop so we could get started on it when we found this other issue. I've got most of the parts including the rear steer Escort rack and pinion which is a nice compact and light piece that I think will work out real well. Took some pictures for the "before and after". I'll probably post something in the build section when I get some time (not sure when that will be).

Thought I'd give an update. Finally pulled the heads off and disassembled them this weekend (been working on the front strut conversion so haven't had time to work on the motor.) Seats were a little corroded but I think they have also moved some. I cleaned up the heads and lapped all the valves. Some of them cleaned up good but some would not completely clean off the seat all the way around. I'm going to take them to a friends place who has vacumm test set up so I can see if they are going to seal. May be due for a valve job. Something else I noticed is that right between the two valves the pointed ridge in the chamber had a crack in it. One chamber even had a small piece of aluminum that was loose but caught between the two seats. I pulled it out so it wouldn't fall in the motor. Anyone else notice this on P-51's?

512Fairlane wrote:Thought I'd give an update. Finally pulled the heads off and disassembled them this weekend (been working on the front strut conversion so haven't had time to work on the motor.) Seats were a little corroded but I think they have also moved some. I cleaned up the heads and lapped all the valves. Some of them cleaned up good but some would not completely clean off the seat all the way around. I'm going to take them to a friends place who has vacumm test set up so I can see if they are going to seal. May be due for a valve job. Something else I noticed is that right between the two valves the pointed ridge in the chamber had a crack in it. One chamber even had a small piece of aluminum that was loose but caught between the two seats. I pulled it out so it wouldn't fall in the motor. Anyone else notice this on P-51's?

If you are talking about the point of alum., in the chamber, right between the two seats, yes it's pretty common for that area to degrade in racing engines. More specifically, it is a sign of detonation. It could be the result of running too much timing, or not enough octane in your gasoline. Another sign of what I'm suggesting is that you said you believe the seats have moved around or migrated. Those clues go hand in hand.

Charlie

That's kind of what I was afraid of Charlie. There is some slight pitting also in a few of the chambers that makes be think there may have been some detonation at some point. Its not real bad but it is there. I'll see how the seal test goes.

The pitting in the chambers, probably looks like porosity holes, and yes that is a sign of detonation. You'll see that around the spark plug and also opposite the spark plug on the cuspid. The heads don't need more than a true 29* of timing.

Charlie

have the valve job touched up...it is possible that the seats have moved.

We checked them today. Most of them are leaking. Are you pretty busy Charlie? I'll be giving you a call.
Thanks, Mike.

Send them.

Charlie

Mike,

We got them today (Friday) and I just got them unboxed.

Later,

Charlie

Thanks Charlie.