Leak Down Test Results - #8 at 40%
 

I am in the process of disassembling the L48 in prep for transferring the cylinder heads, retro-roller cam kit and other items to the re-manufactured 4-bolt 80-85 short block.

My brother-in-law suggested we do a leak down test while the heads are still on the L48 short block in event the heads need attention and to get an idea of 'what went wrong' to cause the engine to consume oil and to foul #8 spark plug so badly.

Leak down was performed with 95psi on each cylinder using a Longacre 73010 Engine Leak Down Tester. I like this tester as it has a valve you can close to turn off the air pressure and only have to disconnect the hose going to the plugs. I had a $30 Harbor Freight tester (junk) that would only allow a max of 20psi. Since the cylinders regularly see 160psi or more compression pressure, 100psi seemed more realistic.

The test results (spraying WD40 on the backside of the intake valves):

#1 - 15% - light foaming of the WD 40
#3 - 15% - " " "
#5 - 12% - no visible foaming
#7 - 16% - light foaming...

#2 - 13% - no visible...
#4 - 13% - no visible...
#6 - 15% - light foaming...
#8 - 40% (FOGGED the WD40 out of the intake port into the oil galley of the engine)

I did some research and it would appear 15% is the ballpark for a healthy street cylinder head. 12% appears the ideal % leak down. Bro' in law says NASCAR is close to 0-5% but they spend more on their cylinder heads than I make in a year.

The cylinder heads were rebuilt in the fall of 2013 and I haven't put that many miles on the car since due to the oil consumption issue that was NOT resolved with a top-end refresh. It was improved but not resolved. At that time, the DART Iron Eagle 180cc iron heads received all new springs, keepers, locks and the better valve seals from the retro-roller cam kit. The machine shop in Springdale, AR, cleaned the castings, lapped the valves, installed the cam kit parts along with new guides, ductile iron valve seats and shimmed the springs.

I am going to pull the heads with particular attention to the #8 cylinder to see if there are issues with the piston/cylinder that caused #8 to leak so badly. The spark plug was heavily fouled. All eight spark plugs had oil on the threads and the other seven plugs had oil fouling but #8 was the worst by far.

At this point, I want to have the cylinder heads get some light work/cleanup to ensure they are ship shape before I drop them on the new short block. Bro' in Law suspects the moly rings on the L48 were either installed/fitted incorrectly or the rings never seated properly (possibly due to NOT cleaning the cylinders prior to reassembly-possible boring residue left from machining). The block was bored .020" over in 1999 and got new +.020" Speed Pro H345NP pistons and Hastings Moly Rings along with a rebuild kit with all name brand parts.

Are you getting a new short block or machining the existing one?

Ted -
I've never seen a valve leak at 40% unless it's severely burnt or damaged. Have you verified that it's valve leakage and not leakage going past the rings..? If you have 40% blowing by a valve, you should hear the air hissing out the tailpipe or up through the carb. If it's going by the rings, you'll hear the air hiss from the oil filler hole.

Lars

Edit -
Never mind - I see you verified that it's an intake valve issue with the WD blowing out forcefully from the valve. Wow... that's some impressive leakage...!

Ted why didn't you use 100 psi it makes the math easier

your numbers seem high I've kind used the refresh at 10 percent rule

I posted my 383s numbers after 2 years of abuse and lots of miles and all the cylinders were at less than 3 percent. Just afr 210 heads with a big solid roller and I have heard it in the 7500 rpm rev limiter.

my 434 Motown sbc was starting to put out blue smoke out on the track down shifting. It was about 3 years old the leak down was all less than 7 percent. Upon tear down it needed new valve guides and the ring end gap had opened up quite a bit. The tiny 1.5mm rings don't seem to last. The guides really get abused with. 685/.714 lift

ipull the heads. lay em on their side. fill ports with water. does it run past the valves? virtually all valves could use disassembling and re-lapping after any kind of mileage. not hard to do. valve spring compressor is a lot cheaper than a machine shop.

I have a remanufactured .040" over short block on the engine stand. I wanted to do a leak down on the heads before I pulled them to see the condition of the valves.

I plan to take the heads to a speed shop for some rework. 'Special attention to #8 as that intake valve appears burnt/damaged.

NOTE: The rebuilder in 2013 shimmed all springs. I am wondering if he failed to shim this spring. I expect to perform a closer exam when I pull them today.

I'll see what the speed shop says. It will be good to get the valve leakage minimized. Although I won't be reusing current short block, I plan to do a post mortem on that cylinder and all cylinders as I suspect the rings due to the oily spark plugs. Will inspect the guides (which were all new in 2013) also. Less than 1k miles since the 2013 cylinder head rebuild. The short block has about 34k miles since 1997 rebuild.

I agree Lars. Bro' in Law David applied the WD 40 to backside of intake valve and when I connected the leak down, it produced a heavy fog past it along with a steady rush of air. I'm pulling the heads today and may go ahead and remove the spring packages to get a better look at all valves, guides and seals. The seals were the type that is fitted over the top of the guide (came with the Comp Retro Roller kit).

that is really sad to fall apart in so few miles it's also sad that you never drive your vette I enjoy long drives. I have driven more than 1000 miles in one day and for years my vette was a daily driver. I think that my 1979 vette has 176,000 on the clock and new on the lot it had 3.2 miles

Agree. It has some ills that I am hoping to resolve with this rebuild: oil consumption, trans oil leak and radiator leak. All getting attention this time.

In the area that I live, having a machine/speed shop go through a set of heads is very expensive, I would have to consider going to a set of new aluminum heads. Just something to think about.

I agree. Or new iron Vortecs. But get a valve spring compressor and check the heads yourself. Valve guide play you can barely feel is acceptable. You will know a bad guide first time you wiggle it. Fill ports with water for quickly leak test. A couple drops after a few seconds is normal. Running right out is a bad valve. Then pop the springs and see the what the seats and valve faces look like. But spending money on OEM heads, unless for originality is a waste.

Lars, Sent you an email. If you have bandwidth, may send the q-jet for freshening as it has been 16 years since you rebuilt.

I took the heads to a local shop "H.P.S." today. I had put a tag on #8 intake valve so 'Matt' could keep that head straight from the other.

So far, after examining #8 valves/parts:

1. #8 Intake and Exhaust valves were 'slightly' bent. Matt was able to clean them up and resolve the slight bend. He says they could have been that way from recent rebuild OR from even a backfire. He will inspect the rest.
2. The PTFE valve seal is wiping the exhaust valve so clean that it is too dry. I am instructed to get a set of 11/32-.530" PTFE seals to let just a little more oil on the exhaust valve to lubricate in the guide.
3. Matt says the leaking rings could account for 10% points of the leakdown across all cylinders. He noted the valves do not seat as cleanly as they should and expects to verify/remedy with the valve job.

Matt is performing disassembly today and Tuesday and plans a valve job. He will advise on what he finds/recommends beyond the slightly looser PTFE seals and the standard valve job. He says beyond cleaning the chambers and ensuring flat head surface, he doesn't expect to have to shave the heads since it is less than 1k miles since the 2013 cylinder head refresh.

NOTE: Matt also suggested he may 'hone' the guides a bit to ensure they are not too tight and the dimensions are true to support the valves. Also, that the valves are properly shimmed. I expressed concern the last builder in 2013 didn't focus on details as much as they should have. He is giving them a good going over.

I like the leak down test .tried to do it on my car.every time I gave it 50 psi or more the motor turned .what did you do to stop the motor from turning .I tried at the top of the stroke and at the bottom. motor moved each time.my motor has 100,000 on it.

I had all of the valves closed on all cylinders (removed all of the rocker arms) so maybe that helped. The engine was also in the car but I had all the fan belts off, plugs out and both intake and exhaust manifolds removed.

When you do the leak down test you should have the cylinder at TDC. If it is at TDC or very close the piston should not move.

yes I had the piston at the top .valves closed .when I gave it air the piston moved down and the valve opened.

I got the heads back on Thursday. $375 to address the following:

1. ALL valves slightly bent in the same manner. 'Matt' advises they were probably a bad lot installed by the initial builder I purchased from. He was able to clean them all up without replacing. Tumbled them and also resolved all run out.
2. ALL iron exhaust seats installed by shop in 2013 had single-angle cut. He cleaned that up and made it 3-angle.
3. In the intake runners, there was a machine mark about 1" inside ahead of the valve that added turbulence (he tested on flow bench). He machined/blended this to improve the flow behavior (all 8 intake runners).
4. The 5/16 PTFE valve seals were too tight on the valves; caused exhaust valves to be particularly dry of oil. He had me purchase 11/32 seals to mount over the .530 guides. It will have a 'puff' on start up but will ensure the valves are not running dry.
5. He tested all valve springs and all were within 5lbs of the appropriate pressure for my retro roller cam.
6. He cleaned up the intake seats also

Very disappointed in the work done by the shop in AR. $700 for that 'work' and this $375... I hope this is the last work on these heads.

Performing leak-down on the fresh short block today.