vettebuyer6369

One short message... keep your responses directed towards the OP and his questions. Posts remotely directed towards ongoing personal hostilities, even if creatively worded, will result in edits and vacations. The staff will not continue to spend time following these conflicts.

2 different mods have had to address this thread already and we have received multiple complaints. Stick to the subject, please.

bmans vette

Thanks for the pics but they have not been in long enough to give any real analysis. I was thinking the ones you replaced these with. Sorry about that.
Cannot tell from pics but are any of these wet with oil?
Did you try putting your finger over each hole and cranking the engine to see what blows out? Any oil might be a broken oil ring which what others have suggested.

I still keep coming back to the idea that you will not know until you pull the heads.
Do that ONLY if YOU feel confident that you can reassemble the engine again.
Taking the heads to a competent machine shop will give you lots of feedback.
And posting pics of the insides of the cylinders/walls/pistons/heads/valves,etc.... here will give us a better chance to see if rings are in fact the issue. Or if it is something else.
It would help if you had someone with a little more tech experience to help.
Keep us posted.

Good luck

Bman

cardo0

Plugs look like their black with soot and wet with fuel. Since the engine runs well until 3500rpm then backfires has me wonder what the carb secondaries are doing. I believe the secondaries start to come on near 3500rpm. Could be a carb problem as well as a dist problem or a vlv spring problem. I wouldn't even look at the bottom end until i resolved the top end. A rebuilt bottom end still wont fix the problems with the top end.



This post wont be edited by cardo0 at anytime.

bluedawg

Im with mako on this one, It sounds like rings as far as the leak down test, but if it ain't smoking you might get a few more miles out of her before you need to rebuild. I'd check the cap , rotor, timing, wires, mechanical advance weights and sings, vacuum and as was mentioned the secondaries on the carb, but you've checked all that so we're back to thinking on it. What's your timing set st and what's your vacuum reading?

jrs420454

Update: I had a chance to re-check my leakdown result (on cyl #4) and I'm pretty confident that the initial reading was valid. I used a plastic straw in the plug hole to verify TDC and got the same reading as before (44% leakdown, all air seemed to escape from the valve cover).

As a check, I took a reading from a cylinder which was NOT at TDC ( #2), and got a cylinder pressure reading of close to zero (full leakdown), and the air was clearly escaping from the exhaust. I just wanted to ensure that, if air was escaping from the exhaust or intake, I'd be able to hear it.

So I'm pretty confident that the leakdown result of cyl #4 is valid, and I saw no reason to re-check the other cylinders, or the ignition timing, advance, etc as it seems pretty clear that I have a lower end issue.

I removed the valve covers, and things seemed intact, visually anyway. No broken springs were evident, though the inner springs are tough to see. Valve spring photos are of cyl #4.

Any more thoughts before I proceed with the engine removal? With leakdown reading like this, is there any real benefit to going back and checking timing, advance, inner valve springs, etc? Thanks!


To answer some of the previous questions:

bman: the plugs that were previously installed are pictured (with the white insulators). No oil is evident on the electrodes of any of the plugs (either set).

cardo0: I ruled out the carb as an issue. An earlier part of this process was to have a Q-jet set up by a reputable builder, that was to be dialed in for this particular engine. Unfortunately his name escapes me, but I could dig it up. In any case, the car ran the same with the new carb as it did with the old one.

bluedawg: as I recall, the ignition timing was set at around 2-4 (initial), which was retarded a bit to deal with today's gas. I don't have the advanced number, or the vacuum number, unfortunately. Cap, rotor, wires, coil, points, condenser, plugs and carb have all been changed.

Bullshark: I could remove the springs and check the inners before going further, but since the leakdown test is indicating lower end issues, maybe I should just address the heads when the engine is apart …

jrs420454

63mako - the leakdown test was done with all plugs removed.... I didn't know that would make a difference. If I reinstalled the other 7 plugs and repeated the test, should I expect a different result? Thanks -

zwede

I don't see any reason to leave the other 7 plugs in. Only time it would be interesting is to check if you have a blown head gasket between two cylinders. In that case you'd see different readings when the neighbor plug was in.

There's also value in checking leak down outside of TDC. You will have to lock the engine (easy if it's a manual, not so easy if automatic. You can probably put a socket on the crank bolt to hold it) and remove the rocker arms. When I did this on my engine I had some cylinders with 90% leak down about 30 dgrs off TDC. My cylinder bores had more wear down a bit.

After the rebuild before break-in all cylinders tested 4%-6% wherever the piston was.

ajrothm

There is so much FAIL from the responses in this thread it's not even funny... Wow..

OP...
Before you start diving off into an engine rebuild or a head rebuild on an engine with 200 psi compression, let's start with fixing your carb and your potential ignition issues.. Get the car to run clean past 3500.. Then drive it and see if its down on power...

Black fouling spark plugs in no time is almost always a carb problem...something is not right with the carb... It's either idling too rich or running way too rich at part throttle cruise.. That's what is killing the plugs....I would go over the ignition system very closely and replace anything that is needed, correctly set the points and the timing.. Verify your mechanical advance is working and not stuck.

Fix all the little stuff first... Then worry about the engine "rebuild".. Leak down tests are usually inconclusive at best and their accuracy is very dependent on the procedure. Do you have some leak by? Ofcourse... Is if enough to warrant splitting a 60k mile, original engine? Not likely.

Personally I'd be more suspect of the cam having wiped lobes myself.. That will still allow it to idle "ok", but it will have no power, it will miss up top and it will kill plugs.. I would pull the intake and try to inspect the lobes as best as possible... However I would do this AFTER I perform a good carb/ignition tune up.

If it did wipe a cam, then a full rebuild is necessary.. We are going thru this right now on my dads 396/425hp 65'... The original solid flat tappet cam lost some lobes and the shavings took out the bearings.

Get the timing straightened out as well... 2-4* initial is nothing! If the mechanical advance is not working then you have no timing at idle(killing plugs)... You just need to go thru everything on this thing. Is it possible the engine is hurt? Sure... But I doubt it...

Anyway, stick to the basics, do some tuning and report back... Don't start ripping heads off and pulling the motor...

63mako

You leave the plugs in to maintain TDC. When pressurizing the cylinder with no plugs it will want to turn over. If it is in park or in gear that will hold it at TDC also.

63mako

Leakdown testing is a much more accurate test for how well your engine in sealing than a compression test and tells you exactly where the problem is. If he was under 30% on all and uniform I would say let it go. 44% and 66% are big problems. He has a ring issue in those 2 cylinders. Should really be under 20% on all.

http://www.carcraft.com/techarticles...akdown_tester/

ajrothm

I agree on the leak down test as far as diagnosing the issues... IF the test is done correctly...--that's where the problem lies... Too much room for error in the procedure...not to mention the engine turning over etc etc.

If the OPs engine really has a cylinder with 66% leakage, yes that cylinder has a major issue, however I seriously doubt it would build 200 psi cranking pressure if the rings/valves were leaking bad enough to yield 66% leakage.

I would start with the easy/obvious stuff first...

Fwiw on my LS6 (LS) I had 30% leak down on #5 & 7, yet it had 60 psi cranking pressure in one, 90 psi in the other.. Turned out to be broken ring lands on both pistons in between the compression rings. It still idled well, didn't smoke and actually ran ok, just down on power and a ton of blow by into the crank case...

The leak down test was very misleading...lol. 30% leak down is bad but didn't indicate how bad it really was.. The compression test told me it was hurt right from the get go..

More then one way to skin a cat...

carbster09

Rebuilding a collectable LS5? I rebuilt mine that had less than 46,000 miles. Why, because its what we do! I wanted a little more, ok more than a little more hp, I wanted it done "my way". The engine still looks stock, has the OEM Qjet, painted vlv covers and a painted Holley Street Dom, which almost looks stock. But the nearly 500 hp on an engine dyno, is NOT stock. And its a whole lot better! I am also running MacJacks shorties .. a nice roller cam from Comp and some trick head work. It revs like a demon even with the all forged USA made stroker assy! I would not want to go back to stock. Now if I could only have the traction.