85 needs an engine...what are my options?
08-07-2018, 03:23 PM
#1
Burning Brakes
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85 needs an engine...what are my options?
So I just got word from the mechanic that the engine (128,000 miles) in my corvette is down to 7 cylinders due to cylinder 5 being at 75 pounds of compression. Obviously a rebuild or crate engine are necessary, but what are the best options moving forward? I want to do everything right but also want to be mindful of cost as I'm not made of money. Here's a link to the original thread: https://www.corvetteforum.com/forums...e-project.html
thanks for the help!
thanks for the help!
08-07-2018, 04:15 PM
#2
Melting Slicks
Be sure you double check the valve lash before replacing the engine, over tightened rockers can also cause low compression. Easy to check and won't cost any money, to rule them out as a cause.
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
Last edited by DMITTZ; 08-07-2018 at 04:16 PM.
08-07-2018, 04:51 PM
#3
I personally wouldn't jump to the conclusion that one reading, in one cylinder, indicating low compression, by one mechanic calls for an automatic rebuild. I would at a minimum, get a second opinion, that is, run a second compression test, preferably by a different mechanic. run a wet and dry compression test to determine if it is rings or valve leakage. in addition, run a leak down test to get a better understanding of the engine's condition. because of the cost of a rebuild (or a crate engine), proceed with caution -- just my 2-cents. 
Last edited by Joe C; 08-07-2018 at 04:52 PM.
08-07-2018, 05:26 PM
#4
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how fast do you need it back on the road? if there is no time limit then pull the motor and no a basic rebuild. if all it needs is a hone job with new rings, barrings, valve job, and other ware items you could get off cheap on the parts bill. but labor to do it could eat it up. you could also buy a basic 350 crate engine from summit or jegs and swap over what you can and you could have that done in a weekend
08-07-2018, 05:54 PM
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Its super common on L98s to pooch the head gasket on those cyl, how does he know it "needs a motor"!!
08-07-2018, 07:24 PM
#6
Instructor
I would at least remove the head on the side with the low reading to see what it needs. It could very well just have a cracked valve which isn't too expensive to repair.
08-08-2018, 12:20 AM
#7
Melting Slicks
The VERY FIRST THING I'd do is pull the valve cover and see if there was something valve train related...and I've seen all this on engines of similar mileage, rocker off valve stem, rocker arm not compressing valve, both of which can be an indication of a rounded off cam lobe...which tends to happen to the #7 (and #8) cylinders since they are farthest away from the radiator / water pump and run the hottest. The second thing I'd do is get is a new mechanic who can diagnosis the cause, and not merely the symptoms, of a problem.
At 128,000 miles the engine may need some work, cam / head gasket / valve job but it sure as hell shouldn't need a new engine (or complete rebuild for that matter)
At 128,000 miles the engine may need some work, cam / head gasket / valve job but it sure as hell shouldn't need a new engine (or complete rebuild for that matter)
Last edited by mtwoolford; 08-08-2018 at 12:25 AM.
08-08-2018, 12:32 AM
#8
Burning Brakes
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how fast do you need it back on the road? if there is no time limit then pull the motor and no a basic rebuild. if all it needs is a hone job with new rings, barrings, valve job, and other ware items you could get off cheap on the parts bill. but labor to do it could eat it up. you could also buy a basic 350 crate engine from summit or jegs and swap over what you can and you could have that done in a weekend
The mechanic that that looked at it is trusted, you tend to have built connections with a body shop in the family and that's who has the car now. He just swapped engines in my dad's 62 falcon and really isn't pressuring us into doing anything one way or the other with it. A compression test during issues last year showed everything in tolerance, but there was a cylinder off from the others. I figured it would need a rebuild eventually after it ran low on oil coming back from Indy awhile back, but was hoping it would get me to at least the wedding.
As for power, I'm not sure it's had stock power since I have had it, but it's certainly been fun with what it had. I wouldn't be opposed to more. My dream setup is a new LT1 with a 6 speed auto(no room for a clutch with size 14s in the small footwell) out of the new Stingrays. But obviously now is not the time for that. Thanks for all of the responses
08-08-2018, 02:49 AM
#9
Melting Slicks
The kicker is I need it ASAP, it's the getaway car for my wedding in October. I would prefer to rebuild what's in it but I want to be economical. I definitely want to keep the car fuel injected. It seems the crate stuff are all designed for carbs or just straight LS/LT series. Older posts show the ZZ4 from Chevrolet performance was the go to replacement but that's discontinued.
The mechanic that that looked at it is trusted, you tend to have built connections with a body shop in the family and that's who has the car now. He just swapped engines in my dad's 62 falcon and really isn't pressuring us into doing anything one way or the other with it. A compression test during issues last year showed everything in tolerance, but there was a cylinder off from the others. I figured it would need a rebuild eventually after it ran low on oil coming back from Indy awhile back, but was hoping it would get me to at least the wedding.
As for power, I'm not sure it's had stock power since I have had it, but it's certainly been fun with what it had. I wouldn't be opposed to more. My dream setup is a new LT1 with a 6 speed auto(no room for a clutch with size 14s in the small footwell) out of the new Stingrays. But obviously now is not the time for that. Thanks for all of the responses
08-08-2018, 01:29 PM
#10
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08-08-2018, 02:42 PM
#11
Melting Slicks
unless its got something goofy, like vortex heads that have there own dedicated intake bolt pattern, I'd say yes, but I'd check for sure; Vortex heads aside, around '85 there was a change in in the center two intake mounting bolts; pre 85 (?) all intake mounting bolts were drilled at the same angle, perpendicular to the intake mounting surface on the head; post 85 (?) the center two holes were drilled at a more upright angle; the accepted mod was just to elongate the center two mounting holes in the intake manifold. Don't know whether that's an issue with your TPI. The only other (possible) issue could be the camshaft compatibility with your computer /TPI set up....I don't think there would be an issue, but I'm no TPI guru....others who are, can chime in here...but a cam swap would be easy enough...and cheap enough since the lifters are new and wouldn't need to be replaced.
After looking at this engine, the (carb) manifold recommended is usable on all pre 1986 heads and appears to be the earlier style with all the intake mounting holes drilled at the same angle, so I assume that a 1985 TPI would bolt up...but better check those two middle mounting holes just to be sure.
After looking at this engine, the (carb) manifold recommended is usable on all pre 1986 heads and appears to be the earlier style with all the intake mounting holes drilled at the same angle, so I assume that a 1985 TPI would bolt up...but better check those two middle mounting holes just to be sure.
Last edited by mtwoolford; 08-08-2018 at 02:56 PM.
08-08-2018, 09:39 PM
#12
Safety Car
The heads in your '85 are iron, and are know as #624 heads, by their casting number. These heads have a bad reputation for cracks, especially if overheated. I'm guessing that may be the reason for your low compression.
Since you trust your mechanic, he probably knows of a good engine rebuilder in the Cincinnati area. The SBC engine is so common, they may have one in stock that would meet your needs. If they don't have one in stock, I'll bet they could build one to your specifications in a very short time. If you go for the rebuild idea, your builder may be able to use #993 heads, which were used in the '79 Corvette. More durable, with the same compression and valve sizes, but better port design, too! Balancing an engine is an option, but I'd suggest that's a worthwhile request if one is being built for you.
Have you asked your friends at your Cars & Coffee get-togethers for their suggestions?
Since you trust your mechanic, he probably knows of a good engine rebuilder in the Cincinnati area. The SBC engine is so common, they may have one in stock that would meet your needs. If they don't have one in stock, I'll bet they could build one to your specifications in a very short time. If you go for the rebuild idea, your builder may be able to use #993 heads, which were used in the '79 Corvette. More durable, with the same compression and valve sizes, but better port design, too! Balancing an engine is an option, but I'd suggest that's a worthwhile request if one is being built for you.
Have you asked your friends at your Cars & Coffee get-togethers for their suggestions?
08-09-2018, 06:59 AM
#14
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Be sure you double check the valve lash before replacing the engine, over tightened rockers can also cause low compression. Easy to check and won't cost any money, to rule them out as a cause.
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
08-09-2018, 05:39 PM
#15
Burning Brakes
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Be sure you double check the valve lash before replacing the engine, over tightened rockers can also cause low compression. Easy to check and won't cost any money, to rule them out as a cause.
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
Are you planning to do the work yourself or have someone do all the labour for you?
Another question are you satisfied with stockish HP or would you want more HP if your going to the trouble of a rebuild?
If you are doing it yourself, and the engine is still in running condition (with low compression) you may be able to salvage most of the parts and do a very cost effective rebuild. If your paying someone to do the labour then a crate engine starts to look attractive as labour costs can really add up. Of course adding HP can get expensive also...
I will suggest that if you have the ability to at least R/R the engine you will save quite a bit, regrdless if you go with a crate or rebuild your motor.
let us know...
08-09-2018, 11:47 PM
#16
Melting Slicks
So right now I’m working with the mechanic to determine why that cylinder lost compression. There’s no coolant in the oil or white smoke so I’m assuming it isn’t a head gasket. In regards to labor, this stuff is a little over my pay grade. Most of the other stuff that’s gone wrong my dad or I have been able to solve, but this isn’t one. I’m okay with the stock power it’s making, but more is never a bad thing. I want the vehicle to still be reliable enough to daily if needed(no, it’s not my daily). If Chevy still sold the ZZ4, I would likely already have it on its way as it came with L98 heads and seems to be the easiest swap in. The engine never did knock or anything, but it did have a tick since it ran low on oil in April of 2017. I have put a couple thousand miles on the car since that time with no noticeable issues until now
08-10-2018, 08:50 PM
#17
Burning Brakes
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here’s a copy of the receipt from pickup today
08-10-2018, 08:51 PM
#18
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Just goggle Chevy ZZ4 crate engine. There are plenty of ZZ4 engines out there for sale; HOWEVER any zz4 or any other 1986 up engine will involve several parts swap; number one is that your present engine and oil pan are designed for a two piece rear seal, which won't work on an later engine. So even if the crate engine comes with an oil pan, at 8 and 1/2 inches it will be too deep for proper ground clearance, and you will have to source a corvette pan which is 7 inches deep and designed for a one piece rear seal; also, you will, at a minimum, need a matching oil pump pickup for the pan; and a flywheel / flexplate designed for a later one piece rear oil seal crankshaft. Nothing too difficult there; just something to be aware of.
