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This spring (soon as the snow melts) I want to get the Vette in for an engine rebuild.
At the end of the summer it was using too much oil and when I put the right foot down I'd drop a good cloud of smoke.
I have had a hard time finding a good mechanic and only want to do this once and do it right. Since its above my Technical limit I need to hire it out.
I begrudgingly joined facebook (I don't social media) and did find a Minnesota Corvette group with some very nice folks. My current engine was just rebuilt in 2018 so mostly high end newer parts ( I have the build sheets).
I inquired about a rebuild and have had a couple offer their services. One was laughed at by another member and the other seems quite knowledgeable, unfortunately I am not. That being said, was hoping for some guidance through the project.
What can I expect for a ballpark cost? $3K -$5K ?
What questions should I be asking?
What do I need to brace myself for?
Engine information - LS5 - 454 BB. Some of the parts already installed are Crower competition forged cam and Manley forged rods. I am a little leery of the Carburetor (SMI Q-Jet) after speaking with the original Mechanic who did the last rebuild (said had major balancing issues with the bleeder)
If it was rebuilt in 2018 and is smoking badly, something is wrong -- unless you've put 100k miles on it since then. You may have non-seated rings or the valve guides were not replaced. Compression and leak-down tests plus a close examination of the spark plugs would be in order before anything. If it is worn guides then that's a lot different than rebuilding the whole thing.
Have you talked with the previous builder about the oil consumption?
Last edited by barkingrats; Jan 18, 2023 at 04:28 PM.
If it was rebuilt in 2018 and is smoking badly, something is wrong -- unless you've put 100k miles on it since then. You may have non-seated rings or the valve guides were not replaced. Compression and leak-down tests plus a close examination of the spark plugs would be in order before anything. If it is worn guides then that's a lot different than rebuilding the whole thing.
Have you talked with the previous builder about the oil consumption?
We did a compression test on it this summer and it was good.
It isn't smoking badly, only when I really jump on the accelerator. The previous owner (former member here) did not have this issue.
The vehicle sat for a period of months and I accepted delivery in December. I was quite excited to receive it so jumped right in and and put it on the highway (20° F out) and proceeded to hammer the the throttle.
Tach went nuts, snapped the needle in half and that is when I believe I damaged it.
I did put a little over 5,000 miles on it this summer. I use over a quart per full fuel tank. No noticeable smoke when driving.
A bit of smoke on hard acceleration isn't that unusual on an engine that sits or just idles a lot. You're burning off the schmoo that has accumulated on the spark plugs and valve tops - plus you could be running rich which will also emit smoke.
Do you think you "over revved" it and that is the when the issue started? If you don't hear any new ticking, clicking, rapping, or knocking, especially under load, then you likely didn't damage any of the rotating components or their bearings. Pull the plugs and see how they look. Wet & oily is likely indicative of worn valve guides or damaged/missing seals. If you post pics of them, you'll get some feedback on where to go next.
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I would start with a valve job. What color is the smoke and the smell....dark is oil or very very very rich burn and is usually the heads. White is water or blow by and is rings or a crack in the heads or block......
If the heads are cast and you are concerned with numbers matching have them rebuult at a machine shop...not a grage or facebook buddies house.
If its not a collector year or there isnt a numbers concern go with a 265 275cc intake volume small chamber head. 115 to 119cc.
Good heads take a while to get currently expect to pay $2300 for the heads and $200 for good gaskets...dont buy cheap chinese heads, you may be able to find a good shim gasket for less to keep the qwench near stock.
Before buying stem seals, this could be as simple as a failed Intake Manifold Gasket. More specifically, the bottom edge.
If that is the case, this issue will show up on the plugs (and out the exhaust).
A leak at the bottom edge of the Intake Gasket is somewhat common. It does not show up using the propane bottle leak test at the top of the gasket.
However, this type of leak issue may show up on a vacuum gauge as a jittery needle.
This is why it is so important to apply a good sealant on the whole gasket, both sides and not just around the ports.
It could be just one cylinder, it could be all eight burning oil from the lifter valley.
I would say your first step in diagnosing is to hook up a vac gauge.
Then pull and start reading plugs making note of which cyl is doing what.
This engine needs to be leaked down......
I suggest you have someone remove the engine and then take it to a reputable engine builder. Most engine builders do not touch the actual car........
Skip trying to find a "mechanic" to do all........this is a potential rabbit hole of peril and money.......
If it is smoking under hard acceleration then the rings have lost seal.....for whatever reason......a quart every tank will show up on a leakdown tester.
I assume you mean this has a Forged Crower crank (not cam) and Manley rods......both are very high dollar pieces....and the pistons should be equally high dollar.......it may have been honed improper or someone F'd up and put a light tension oil ring in it......
A good engine builder will be able to diagnose the problem and not charge you for a complete rebuild.........it may just need a nice "ten pass" diamond hone and a good set of Total Seal rings......
This engine needs to be leaked down......
I suggest you have someone remove the engine and then take it to a reputable engine builder. Most engine builders do not touch the actual car........
Skip trying to find a "mechanic" to do all........this is a potential rabbit hole of peril and money.......
If it is smoking under hard acceleration then the rings have lost seal.....for whatever reason......a quart every tank will show up on a leakdown tester.
I assume you mean this has a Forged Crower crank (not cam) and Manley rods......both are very high dollar pieces....and the pistons should be equally high dollar.......it may have been honed improper or someone F'd up and put a light tension oil ring in it......
A good engine builder will be able to diagnose the problem and not charge you for a complete rebuild.........it may just need a nice "ten pass" diamond hone and a good set of Total Seal rings......
Jebby
Jebby
Sorry yes, forged crank. Unfortunately the Mechanic that was referred to me last year is the one who told me I needed the rebuild, I just don't trust him to do it.
I'll ping the FB group and see if I can find a local engine builder as you suggest.
as Heads U.P.said, i would look at the intake manifold gasket first. i mean LOOK at it. do an autopsy on it. remove it carefully looking for signs of leakage along the bottom. if it looks like it was perfect, do the valve seals and check the guides for looseness. i like to glue (sealer) the manifold gasket in place and let it harden. then you are sure it is gonna stay where it is supposed to be when the manifold drops on it. if valves wiggle in the guides, consider finding another set of heads and just throwing the umbrellas on these valves in the mean time. Jebby is rarely wrong but this time i hope he is. piston ring oil loss is worst case scenario and i would consider running it another summer while getting ducks lined up for pulling engine in the fall and spending the winter making the engine compartment really pretty while someone has the engine block. BTW, those piston numbers look like forged 496 pistons. are you sure this beastie is still a 427?
as Heads U.P.said, i would look at the intake manifold gasket first. i mean LOOK at it. do an autopsy on it. remove it carefully looking for signs of leakage along the bottom. if it looks like it was perfect, do the valve seals and check the guides for looseness. i like to glue (sealer) the manifold gasket in place and let it harden. then you are sure it is gonna stay where it is supposed to be when the manifold drops on it. if valves wiggle in the guides, consider finding another set of heads and just throwing the umbrellas on these valves in the mean time. Jebby is rarely wrong but this time i hope he is. piston ring oil loss is worst case scenario and i would consider running it another summer while getting ducks lined up for pulling engine in the fall and spending the winter making the engine compartment really pretty while someone has the engine block. BTW, those piston numbers look like forged 496 pistons. are you sure this beastie is still a 427?
Sounds like very sound advice. It has a numbers matching block but that's about as far as that goes. Was a 454 (LS5) but when I showed the engine build sheets to a local engine guy he also mentioned 496.
I drive cars but don't speak the engine language about pistons being rebored and all that engine stuff
Sounds like very sound advice. It has a numbers matching block but that's about as far as that goes. Was a 454 (LS5) but when I showed the engine build sheets to a local engine guy he also mentioned 496.
I drive cars but don't speak the engine language about pistons being rebored and all that engine stuff
A 496 would result from a 454 getting a 0.060" cylinder over-bore from the stock size (making a 468) plus a new crank that has 1/4" more stroke length (making it a 496). Apparently the build sheets indicate the bore and crank used and that's where the engine guy is making this statement.
You don't need a rebuild but tear down inspection. A bore scope and leak down to look at the rings and cylinder walls. Maybe the rings didn't seat.
Remove the intake manifold and see if oil is all over the intake runners. That's what was causing mine to smoke because the gasket was not installed correctly.
Last would be the intake valve seals. Were the heads rebuild?
A 496 would result from a 454 getting a 0.060" cylinder over-bore from the stock size (making a 468) plus a new crank that has 1/4" more stroke length (making it a 496). Apparently the build sheets indicate the bore and crank used and that's where the engine guy is making this statement.
when you google piston number it comes up as a 496 piston. build sheet doesn't say the stroke.
71 LS5 Engine rebuild
