Best advice -L-36 blue smoke -rebuild time??

[Bill M.]

Re: Best advice -L-36 blue smoke -rebuild time??

Bill-----


They did not; I was extremely lucky on each occasion.

I asked because I worked in the dyno lab at Tonawanda in the summer of 1969 and don't remember broken Mark IV valve springs (we had many) damaging engines. (It's possible some did get damaged, but certainly not all.)

When we broke a piston, it trashed everything except the opposite bank's cylinder head!

The test we were running was a 200 hour durability test. We were not running the engines to redline, just from peak torque to peak power (if faded memory serves).

I wondered if failed springs on the street trashed your L78. Glad to hear it didn't.

[Ken B.]

Re: Best advice -L-36 blue smoke -rebuild time??

After reading all the responses I totally agree with the valve seal replacement. A car sitting for 6 or 7 years probably has seals all dried and worn. Easy fix will in the car..And change those valve springs.

[Duke W.]

Re: Best advice -L-36 blue smoke -rebuild time??

Based on on e-mails with Joe L. and a previous threads on this subject, it should be noted that the ...627 is a "kit" that consists or a dual valve spring and 3964264 "retainer" (GMPD refers to it as a "cap") with integral valve guide seal, so no separate seal is required. Same applies to the referenced 123... which is kit of 16 ...627s.

Expect to pay between $10-15 per ...627, which is a bit pricey compared to small block parts, but installation should result in lowered oil consumption and eliminate the possibility of a broken valve spring. There are also reports that the early valve keys (locks) can fail, so along with the new valve springs, it would be adviseable to by a set of keys (32) part number 3947880.

There is an anomaly in the specifications. Various sources list the seat force as 105 pounds at 1.88", and list the rate as either 267 or 450 pounds per inch; 267 seems low and 450 is way high considering that the L-88 spring has a rate of 330 lbs/in.

If anyone buys these springs or has any on hand can you take one to a machine shop and ask them to test it in a valve spring tester at 1.88 and 1.38". This will allow easy computation of the actual average rate, which is the difference in the two force values divided by 0.5.

All the previous discussions can be found in the archvies by searching 3970627.

Duke

[Keith B.]

Best advice -L-36 blue smoke -rebuild time?-Update

Thank-you again for all this valuable info. I have not done anything yet and took the 66 out for a good highway cruise yesterday and wanted to add some symptoms that may or may not change how I approach the problem.My mechanic has my timing retarded?,something about 36 or 37 degrees, it PINGS allot on acceleration, even with Chevron 94 octane, but is hardly pings if I use 94 + an octane booster. Yesterday, I had it up to 70-85 miles per hour. At 3K RPM upon accleration big puff of blue smoke out of left side only. And this is weird to me once at these speeds/RPM, if you take your foot off the gas completely, a bigger plume of blue smoke on left side. At constant speed - no smoke. My mechanic does not have the gauges for a cylinder leak down test, so I may have to look eleswhere. He wants to take the heads off right away and see what is going on down there but agrees 100% that the valve seals/springs, etc should be changed. Just wanted to add this new info and take your original advice and maybe even take the heads off and look deeper......your thoughts. Thanks.

[Joe L.]

Re: Best advice -L-36 blue smoke -rebuild time?-Update

Thank-you again for all this valuable info. I have not done anything yet and took the 66 out for a good highway cruise yesterday and wanted to add some symptoms that may or may not change how I approach the problem.My mechanic has my timing retarded?,something about 36 or 37 degrees, it PINGS allot on acceleration, even with Chevron 94 octane, but is hardly pings if I use 94 + an octane booster. Yesterday, I had it up to 70-85 miles per hour. At 3K RPM upon accleration big puff of blue smoke out of left side only. And this is weird to me once at these speeds/RPM, if you take your foot off the gas completely, a bigger plume of blue smoke on left side. At constant speed - no smoke. My mechanic does not have the gauges for a cylinder leak down test, so I may have to look eleswhere. He wants to take the heads off right away and see what is going on down there but agrees 100% that the valve seals/springs, etc should be changed. Just wanted to add this new info and take your original advice and maybe even take the heads off and look deeper......your thoughts. Thanks.

Keith-----


I think you mean 36 or 37 degrees TOTAL ADVANCE. If it was retarded that much, it would not run, at all.

If the mechanic does not have the equipment for a cylinder leak-down test, he should, at least, have what's needed for a compression test. A leak-down gauge set-up can be purchased for about $100; a compression gauge for about $20. These are IMPORTANT tests. You won't be able to gauge the condition of the cylinders, pistons, and rings without using one of them.

Removing the cylinder heads might not be a bad idea. It's not a big deal to remove them. It will make it easier to change the seals. Plus, they will need to be removed, anyway, if any valve guides need to be replaced. Even one bad one on each head and the heads have to come off for the work.

However, I'd definitely have the leak-down or compression test run BEFORE any of this is done. That's because you need to KNOW the condition of the "bottom end" before you have the head work done and the heads reinstalled. Otherwise, you could end up removing the heads again to do the bottom end work. VERY inefficient to do things this way. Armed with the information from a leak-down or compression test, you will know BEFORE you remove the heads if you need to go "all the way" and do a complete engine rebuild.

If you determine that you don't need to do a complete overhaul, the one thing I would still do with the short block is to replace the timing set. Your original used a nylon-tooth cam sprocket. Even with low miles, this will be deteriorated by now. However, this has NOTHING TO DO with your oil burning problem---it's totally unrelated.

[Duke W.]

Re: Best advice -L-36 blue smoke -rebuild time??

Take a deep breath, then find a new "mechanic" It's just unbelieveable that a "professional" does not have a leak down tester and is anxious to remove the heads without a thorough diagnosis. Real professionals do appropriate diagnosics before tearing into an engine. The guy must be hurting for business. Good mechanics, like good doctors, don't want to open up the patient unless there is no other alternative.

An old engine might use a little oil and if the valve seals are poor, a puff of blue smoke on accleration, particularly after a few seconds of trailing throttle, is not unusual.

The $64,000 question is: HOW MUCH OIL DOES IT CONSUME?

Have you run an accurate consumption test to determine the number of miles per quart?

Assuming you haven't you need to do so, and get a real leakdown test.

If the leakdown numbers are okay, but oil consumption is less than, say, 600 miles/quart, or you are just willing to throw a few hundred bucks at the blue smoke "problem" the new ..627 spring kits with integral retainer/seal may be installed without removing the heads. This will likely eliminate the blue smoke and eliminate the chance of a spring failure that could lead to serious consequential damage.

However there is some risk. Once the spring is removed from each valve a good mechanic (and I emphasize GOOD) can determine if the valve guides are worn - excessively - and this is the operative word. Any old engine will show some guide wear. The question is whether or not the wear is to the point were new seals will not reduce the oil consumption. In this case you must make a decision to complete the spring/seal replacement or proceed to removing the heads and rebuilding them.

In most cases, unless several guides show really excessive wear, it's best to proceed with the spring/seal replacement and see what happens. If the head ultimately has to be rebuilt you can reuse the barely used ...627 spring/retainer/seal assemblies.

A few years ago when my Cosworth Vega's little 2 liter four got down to about 200 miles per quart (other than the high oil consumption and blue smoke it ran great and even when new used a quart about every 600 miles,) I finally decided to install new valve seals, but I quickly found way excessive guide wear, so I had no choice, but to remove the head for new guides. One guide was so badly worn I was surprised the valve head had not broken off.

Consider that if you scale up the 200 miles per quart from a 2L four to a 427 V8, the equivalent would be less than 100 miles/quart.

With the new guides and a new design aftermarket seals I can't even measure the CV's oil consumption. After having the guides replaced, I was able to lap in the valves, so a complete valve grind was not necessary though I did do a little pocket porting/port matching and had the machinist take a cut off the top of the inlet valves to eliminate the unused seating surface.

It now makes useable power to 7500, but I limit revs to 7000 because it still has the original Tonawanda built bottom end.

In the case of your engine with only 44K miles I would be willing to bet that the guides are seviceable, and the blue smoke is caused from 40+ year old seals that have hardened and cracked allowing too much oil to drain down to the top of the guide. And the last thing I would want to do is let some "mechanic" who doesn't even own a leakdown tester and probably doesn't know jack about vintage Corvettes start tearing apart an original 44K mile engine.

Duke

[Keith B.]

Re: Best advice -L-36 blue smoke -rebuild time??

Duke/Joe: I sincerely appreciate the time and thoughtful analysis you put into my questions. Thank-you very much. I did not get into the qualifications of my mechanic but he does not have a leak down gauge but can do a compression test. Actually he wants me to have a local performance shop conduct a high pressure (Snap-on machine) flush of my engine first, apparently it get allot of crude out but not sure if this will really assist me. Actually, my mechanic runs his shop out of his house, used to have a large HP engine business for 40yrs and grew up in California and used to race these old midyears. I'm fairly confident in his abilities, I just find he is real old school and perhaps has not kept up with technology. However, he is always on me to upgrade things , like go to alum heads, gas line regulator to control fuel pressure into Holley, etc. So I humour him and tell him I want to keep this car factory original, ie when I change the springs he wants to go to a better product then GM, ie Engle or Comp. I like the idea of the GM kit you mention. I'm going to find some place to conduct the leak down test and report back to you, then upon these findings move forward based on the results. I would like to try the springs/seals and see how things go first. Sorry for all the questions....I have never been involved into engine re-building. I love to learn but no nothing about it, much better at detailing the chrome/paint. Thanks guys.....this really helps me.

[Duke W.]

Re: Best advice -L-36 blue smoke -rebuild time??

A 44K mile '66 L-36! Do you know what you have?

With that few miles, I suspect it's probably one of the few original, unrestored, and likely unmolested examples left. Do you know what an original unmolested car like this can go for in one of the big auctions?

It scares the hell out of me, when I see guys like you surrounded by hot rodders who want you to turn your car into a hot rod with a bunch of aftermarket parts and modifications - there goes another one to hot rod hell!

It took GM five years to solve the big block valve spring problem. The ...627 kit did not come out until 1970, but it's proven itself for nearly 40 years in millions of Mark IV engines. They are proven!

Stick with OE or exact OE equivalent replacement parts. Forget the hot rod stuff. Don't mess up your car. Start talking to your local NCRS Chapter guys instead of these backyard bubbas.

You can probably rent a leakdown tester at a local parts store - and you need an air compressor. There are web pages that explain how to make your own leak down tester. It's simple device.

Find a competent shop that can do a leak down test. The leakdown test will probably be okay. Buy the parts from gmpartsdirect.com or whatever and find a competent mechanic who can install the new parts without screwing up the car. It's not that hard a job. Maybe your local chapter guys can refer you to a mechanic who understands old Corvettes and why it's in your best interest to keep yours original rather than turning it into a hot rod with a bunch or useless hot rod catalog parts.

Duke

[Keith B.]

Re: Best advice -L-36 blue smoke -rebuild time??

Duke: I 100% agree and have another Classic Corvette mechanic I can use who completely understands these vintage cars and agrees with keeping these cars original. I will follow your advice completely, as a matter of fact this new mechanic is in alignment with your philosphy completely. GM and OE parts and keep it original, and don't mess with it.Lastly, see my web-site under my profile and my car on the C2 Registry. I'm not going to destroy this work of art, thats why I joined the NCRS and my local chapter and judged my first car in August. I looked for 2 yrs, everyday, to find a one owner, 66 BB car that had 39.939 org miles, no hit, unrestored car, rust free frame, and GM published documentation that produced a 97.7 % T.F. score at last years NW NCRS Regional. I'm NOT going to mod this car. I have all the NCRS publications and whenever I need to repair/replace something I refer to all these manuals and do it to the factory standard. My next big project is going to have it painted, ofcourse in its org silver pearl color that I can still get done in lacquer. I absolutely adore my midyear and never leave it parked alone, and am very cautious when driving in summer only with being an un-hit car. I want to thank-you for your advice, when I get it diagnosed I will let you know what he found. Thank-you.

[Michael M.]

Re: Best advice -L-36 blue smoke -rebuild time??

Valve seals and valve springs may be the issue, but in my quick read of the thread I did not see anyone mention a leaking intake manifold gasket allowing the engine to suck in oil from the lifter valley. Just a thought.

[Duke W.]

Re: Best advice -L-36 blue smoke -rebuild time??

Beautiful car! You're on the right track.

I notice that the option list says CR four-speed, but no listing for Positraction and axle ratio. You can get the info off the axle code or just divide indicated revs at 60 MPH by 775 and pick the closest ratio to the number you get.

I still recall riding in a friend's '67 L-68 Coupe with a CR trans and 3.70 axle circa 1970. To this day I think it was one of the fastest 40-80 cars I've ever been it!

Duke

[Keith B.]

Re: Best advice -L-36 blue smoke -rebuild time??

Duke: Another great observation.......I will update my C2 Registry.....my car has posi and 3:55 ratio that I took off my org window stick and on my dealer sales invoice. I'm told it is a nice set-up to have, as this is my first corvette I would not know any different...........Cheers/

[Joe L.]

Re: Best advice -L-36 blue smoke -rebuild time??

Duke: Another great observation.......I will update my C2 Registry.....my car has posi and 3:55 ratio that I took off my org window stick and on my dealer sales invoice. I'm told it is a nice set-up to have, as this is my first corvette I would not know any different...........Cheers/

Keith----


All 1965-74 Corvettes equipped with Mark IV engines were also equipped with positraction---it was a mandatory option.

[Keith B.]

Re: Best advice -L-36 blue smoke -Compression test..

Fellow Members: This was a very helpful thread for my situation back in Sept and I finally in the dead of winter started to do some diagnostics as per the advice given by Joe & Duke and others. I conducted my own compression test today and here are the findings X 3 per cyc readings:
Factory 427/390, 44,000 org miles, motor never touched since factory, PSI should be according to service manual 160 PSI (new).

# 1- 180, 160, 150 #2- 160,170,180
# 3- 100, 80,90 #4- 190,200,210
# 5- 190, 190, 195 #6- 210,210,205
# 7- 180,200,200 #8- 190,190,205

So, the amateur I'am at this and reading the manual tells me I have a problem at # 3. I then added 1 tbsp of oil injected into the # 3 and did a re-test. Readings were 120,120,120. They went up which I'm lead to believe is not my valves rather most likely my piston rings, etc.

My next thought was to take the top end off, order the GM kit change the springs, retainers, and valve seals as per advice above. Remove the heads and take a look at the top of my pistons. I sense I'm into a complete rebuild which kind of surprises my at this low mileage. The car did sit by the org owner for 7-10 yrs prior to me buying it in 2004.

Your thoughts please on the readings, next steps, am I on the right track......appreciate it !! Atleast I know more today that just guessing before...thanks Duke/Joe, etc !!

[Joe L.]

Re: Best advice -L-36 blue smoke -rebuild time??

Fellow Members: This was a very helpful thread for my situation back in Sept and I finally in the dead of winter started to do some diagnostics as per the advice given by Joe & Duke and others. I conducted my own compression test today and here are the findings X 3 per cyc readings:
Factory 427/390, 44,000 org miles, motor never touched since factory, PSI should be according to service manual 160 PSI (new).

# 1- 180, 160, 150 #2- 160,170,180
# 3- 100, 80,90 #4- 190,200,210
# 5- 190, 190, 195 #6- 210,210,205
# 7- 180,200,200 #8- 190,190,205

So, the amateur I'am at this and reading the manual tells me I have a problem at # 3. I then added 1 tbsp of oil injected into the # 3 and did a re-test. Readings were 120,120,120. They went up which I'm lead to believe is not my valves rather most likely my piston rings, etc.

My next thought was to take the top end off, order the GM kit change the springs, retainers, and valve seals as per advice above. Remove the heads and take a look at the top of my pistons. I sense I'm into a complete rebuild which kind of surprises my at this low mileage. The car did sit by the org owner for 7-10 yrs prior to me buying it in 2004.

Your thoughts please on the readings, next steps, am I on the right track......appreciate it !! Atleast I know more today that just guessing before...thanks Duke/Joe, etc !!

Keith-----


From what you've done and described, it looks to me like you have a problem with the #3 cylinder. I would suspect a broken ring and/or a deeply scored cylinder wall. The "add-a-teaspoon-of-oil" test is not always an accurate way, though, to differentiate between ring and valve problems, so I'm not 100% sure that the problem is related to rings. You might want to remove the heads first and determine if there exists any problem with the valves on the #3 cylinder. At the same time, you'll be able to inspect that cylinder for scoring. If it turns out to be a ring or cylinder wall problem, you'll have to pull the block and do a complete rebuild.