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

[Keith B.]

I'm not an engine expert so I look to the team for best advice.....

I have a 66 vert , L-36 T.F. car with 44,000 original miles. Purchased by me from the orignal owner in 2004. Car had 37,000 org miles in 1987, 39,939 miles when I bought it in 2004. It sat in a garage for 6-8 yrs before I bought it. Engine has never been out of car, never opened up since factory. I have enjoyed putting on 4,000 miles but am now experiencing increased blue bursts of smoke out of my drivers side rear exhaust, and very little out of the RT side tail pipe. There is no smoke when cruising but when you accelerate 2, 3, 4th especially at higher RPM's there is a nice cloud of blue out the rear. I have changed oil (diesel oil as per forum expert) every 500 miles and have now put Bardahl anti-smoke agent in crank that has had some minimal effect. Rings/Valves???

I sense many of you may suggest complete engine rebuild, just a little nervous about getting the right person to protect my stamp pad, etc.

Lastly, What internal improvments would you recommend that will improve performance, but preserve the integrity of the car. ie, should one consider cam changes, what components have you used and recommend??

Any and ALL advice is appreciated....THank-you.

[Joe L.]

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

I'm not an engine expert so I look to the team for best advice.....

I have a 66 vert , L-36 T.F. car with 44,000 original miles. Purchased by me from the orignal owner in 2004. Car had 37,000 org miles in 1987, 39,939 miles when I bought it in 2004. It sat in a garage for 6-8 yrs before I bought it. Engine has never been out of car, never opened up since factory. I have enjoyed putting on 4,000 miles but am now experiencing increased blue bursts of smoke out of my drivers side rear exhaust, and very little out of the RT side tail pipe. There is no smoke when cruising but when you accelerate 2, 3, 4th especially at higher RPM's there is a nice cloud of blue out the rear. I have changed oil (diesel oil as per forum expert) every 500 miles and have now put Bardahl anti-smoke agent in crank that has had some minimal effect. Rings/Valves???

I sense many of you may suggest complete engine rebuild, just a little nervous about getting the right person to protect my stamp pad, etc.

Lastly, What internal improvments would you recommend that will improve performance, but preserve the integrity of the car. ie, should one consider cam changes, what components have you used and recommend??

Any and ALL advice is appreciated....THank-you.

Keith-----


I responded to your e-mail on this subject but I'll just cover it briefly here:

1) I would not assume the engine needs a complete rebuild. Its mileage is quite low and there's no reason to infer that a rebuild is necessary;

2) Run a compression test or, better yet, a cylinder leak-down test to assess the condition of the engine. If it checks out ok, I'd just replace the valve seals. At the same time, you can replace the valve springs. The pre-1970 big block valve springs are very prone to breakage and, if they break, major engine damage can result. So, you can replace them easily at the same time you replace the valve seals. Use GM #3970627. This is a unit which includes valve spring, retainer, and seal. An engine-kit of 16 is available under GM #12371061;

3) The above can be done with the engine in the car and the heads on the engine;

4) When the above is done, you can do a rough check on the valve guide condition by "wiggling" the valve stems. A very slight amount of "play" is normal, but if any valve have more than this, you MAY need to service them which will mean removing the heads from the engine. Even if the engine is otherwise healthy as revealed from the compression or leak down test, you could need valve guide work. I'd say it's unlikely, but possible;

5) I would not consider any engine mods at this stage of the game. The L-36 is one of the best STREET big blocks ever made.

[Stuart F.]

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

I completely agree with Joe on this. At 44,000 miles you should not be any where near rebuild time. I'd go for the valve seals first as you say the car has done a lot of sitting. My 63 has about 44,500 on an L-76 SHP. It has about the same oil consumption as when new. I don't see any blue smoke out the back, but with my foot in it I'm not looking back too much. I followed it once and only saw black smoke when the throttle was tipped. Cars that sit tend more to have dried out gaskets and seals. Also, I once thought my valve springs were getting weak as it would break up at about 6500 to 7000 rpm. Then I changed ignitions and that cured that.

Stu Fox

[Jay G.]

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

I found my 67 L-79 had been sitting in MI. barn since 89. Did the usual stuff when I got it. But was burning oil after my start up. Found the builder put too hi-pressure oil pumpin the car. Engine ran 60LBS of oil pressure all the time. Then I replaced it correctly and rebuilt the 3810 Holley "smaller jets for our 8K foot mnt level". No more oil burning. Now 60lbs start up 30-40 lbs running. Try looking at number of small things after a car been sitting for any length of time.

[Paul C.]

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

I agre. Replaced the valvee. Ny 71 was using 1 quart/150 miles. Did a compression test and leakdown. All the cylinders looked good but oil fouled #8 plug. Pulled the valve covers and the valve seals were original and full of cracks. Am replacing the seals now--should be done by Monday. If oil consumption continues my have to rebuild engine--if not GREAT. Follw previous posters before rebuilding engine/

[R N.]

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

[quote=Joe Lucia (12484);368206]Keith-----



The pre-1970 big block valve springs are very prone to breakage and, if they break, major engine damage can result. So, you can replace them easily at the same time you replace the valve seals. Use GM #3970627. This is a unit which includes valve spring, retainer, and seal. An engine-kit of 16 is available under GM #12371061;

Joe, could these springs be used on a L-72 as well?

Thanks...

[Keith B.]

What is a cylinder leak-down test ??

Thanks guys for the excellent advice, I will follow it exactly before going the whole rebuild route. What is cyclinder leak-down test???

Thank-you....Keith

[Joe L.]

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

[quote=R. Kurt Neiman (38038);368282]

Keith-----



The pre-1970 big block valve springs are very prone to breakage and, if they break, major engine damage can result. So, you can replace them easily at the same time you replace the valve seals. Use GM #3970627. This is a unit which includes valve spring, retainer, and seal. An engine-kit of 16 is available under GM #12371061;

Joe, could these springs be used on a L-72 as well?

Thanks...

Kurt-----


DEFINITELY. These are THE ones to use.

[Joe L.]

Re: What is a cylinder leak-down test ??

Thanks guys for the excellent advice, I will follow it exactly before going the whole rebuild route. What is cyclinder leak-down test???

Thank-you....Keith

Keith----


A cylinder leak down test is a much more accurate form of a "compression test". It requires a cylinder leak-down gauge tool as well as a compressor. The leak-down gauge tools cost about $100-200 and are available from several suppliers. I prefer the DUAL GAUGE type to the single gauge, even though they are the more expensive of the two types.

By the way, a cylinder leak down test is the only type of test which the FAA approves for use in evaluating the condition of reciprocating aircraft engines.

[Duke W.]

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

[quote=R. Kurt Neiman (38038);368282]

Keith-----



The pre-1970 big block valve springs are very prone to breakage and, if they break, major engine damage can result. So, you can replace them easily at the same time you replace the valve seals. Use GM #3970627. This is a unit which includes valve spring, retainer, and seal. An engine-kit of 16 is available under GM #12371061;

Joe, could these springs be used on a L-72 as well?

Thanks...

All big blocks that still have the OE first design single/spring-damper setup with the separate seal should be retrofited with the ...627 assembly, even if oil consumption is acceptable. This would include all big blocks through at least 1969. It's certainly easy to visually inspect what is installed on any big block as the single spring-damper should be easy to differentiate from the ...627 dual spring assembly.

The ...627 eliminates the broken spring hazard and resulting consequential damage that may require a complete engine overhaul if a spring breaks, which causes the valve to drop into the cylinder and this can break a piston.

The ...627 has been the service replacement part for all BB valve springs back to '65 since at least as far back as 1977, which is the oldest P&A catalog I have.

Duke

[Joe L.]

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

[quote=Duke Williams (22045);368288]

All big blocks that still have the OE first design single/spring-damper setup with the separate seal should be retrofited with the ...627 assembly, even if oil consumption is acceptable. This would include all big blocks through at least 1969. It's certainly easy to visually inspect what is installed on any big block as the single spring-damper should be easy to differentiate from the ...627 dual spring assembly.

The ...627 eliminates the broken spring hazard and resulting consequential damage that may require a complete engine overhaul if a spring breaks, which causes the valve to drop into the cylinder and this can break a piston.

The ...627 has been the service replacement part for all BB valve springs back to '65 since at least as far back as 1977, which is the oldest P&A catalog I have.

Duke

Duke----


The GM #3970627 replaced GM #3859911 in November, 1970. The 3859911 was the spring used for all 1965-69 big block applications, except L-88.

Pictured below is a GM #3859911 spring that once resided on my 1968 Chevelle SS 396 L-78 engine. Several of its "brothers" met the same fate and all this occurred with less than 20,000 miles, or so, on the engine.

I have seen folks spend BIG $$$$$ for a set of the 3859911 springs on eBay. I hope they are doing it for use as a "conversation piece". For actual use on an engine, I would not pay $0.01 for a set.

[Duke W.]

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

[quote=Joe Lucia (12484);368289]

The GM #3970627 replaced GM #3859911 in November, 1970.

Is that when it became the service replacement?

When was the ...627 first used in production engines. I've never been certain if is was 1970 or '71 and did the first production use of the ...627 start at the beginning of a model year or was it a running change?

Duke

[Joe L.]

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

[quote=Duke Williams (22045);368294]

Is that when it became the service replacement?

When was the ...627 first used in production engines. I've never been certain if is was 1970 or '71 and did the first production use of the ...627 start at the beginning of a model year or was it a running change?

Duke

Duke----

November, 1970 is when the SERVICE replacement took place and not when the change in PRODUCTION occurred. According to GM, the change in PRODUCTION occurred sometime very late in the 1969 model year. Just when, I do not know. The part number also infers a very late 1969 piece, so that "jives" with the other information.

[Bill M.]

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

Pictured below is a GM #3859911 spring that once resided on my 1968 Chevelle SS 396 L-78 engine. Several of its "brothers" met the same fate and all this occurred with less than 20,000 miles, or so, on the engine.

Hi Joe:

Did the broken springs result in major engine damage to your L78?

Bill

[Joe L.]

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

Hi Joe:

Did the broken springs result in major engine damage to your L78?

Bill

Bill-----


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