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Hey guys so I have an 88 corvette with 180K miles. I blew a head gasket and decided to do a top end rebuild haven’t had any work done yet but we did a leak down test and on the cylinders where the gasket isn’t leaking it scores for the cylinders were between 11-14%. The car doesn’t use any oil and oil PSI in park when warm was usually 28-34. Should I overhaul the bottom end? What do some of you suggest? I’m not super mechanically inclined that’s why I’m on here asking.
Hey guys so I have an 88 corvette with 180K miles. I blew a head gasket and decided to do a top end rebuild haven’t had any work done yet but we did a leak down test and on the cylinders where the gasket isn’t leaking it scores for the cylinders were between 11-14%. The car doesn’t use any oil and oil PSI in park when warm was usually 28-34. Should I overhaul the bottom end? What do some of you suggest? I’m not super mechanically inclined that’s why I’m on here asking.
A lot of times you don't know what you're in for until you pull it apart. You might get lucky and just need head gaskets. Or you might find that the cylinders are all glassy and you need a rebuild. I would pull the heads and have a look. If everything looks good then resurface the heads and put on fresh head gaskets. But don't go into this with the expectation that you won't have to rebuild/replace the whole thing, because you might.
At 180K miles I would imagine that your cylinder bore must have some wear. That Leak Down Number looks great almost "too good" for an engine with close to 200,000 miles. What air pressure did you supply the cylinders with when doing the test? I love the leak down test as it is a good way to measure the wear. If the engine was closer to 100K miles I would support the idea of a top end rebuild but at 200K I would have to say pull the entire engine.
If it were my engine, it would come out for a "winter" rebuild. You have a few months of cooler weather where Corvette use is minimized so it might be a good time, (sorry, maybe not since you are in California). Once the motor is out take it to somebody who owns a machine shop and have them rebuild it back to stock for you. If you fix the top end something else will fail down below with all the power being made by the newer top end. I would find a gas station that you trust and have them remove the engine and later re-install it for you. Then find a good reliable shop to rebuild the engine for you. The more work you can do the less expensive the project will be. If you have the set of 1988 Corvette Factory Service Manuals you can read up on pulling the engine out completely.
Rebuilding it all at once would be a better option in my humble opinion.
A lot of times you don't know what you're in for until you pull it apart. You might get lucky and just need head gaskets. Or you might find that the cylinders are all glassy and you need a rebuild. I would pull the heads and have a look. If everything looks good then resurface the heads and put on fresh head gaskets. But don't go into this with the expectation that you won't have to rebuild/replace the whole thing, because you might.
Yeah I’m with you man I’m letting my mechanic kinda lead me on with this for obvious reasons he’s a pro very well respected. I’m willing to do anything needed so yeah thanks for the words.
At 180K miles I would imagine that your cylinder bore must have some wear. That Leak Down Number looks great almost "too good" for an engine with close to 200,000 miles. What air pressure did you supply the cylinders with when doing the test? I love the leak down test as it is a good way to measure the wear. If the engine was closer to 100K miles I would support the idea of a top end rebuild but at 200K I would have to say pull the entire engine.
If it were my engine, it would come out for a "winter" rebuild. You have a few months of cooler weather where Corvette use is minimized so it might be a good time, (sorry, maybe not since you are in California). Once the motor is out take it to somebody who owns a machine shop and have them rebuild it back to stock for you. If you fix the top end something else will fail down below with all the power being made by the newer top end. I would find a gas station that you trust and have them remove the engine and later re-install it for you. Then find a good reliable shop to rebuild the engine for you. The more work you can do the less expensive the project will be. If you have the set of 1988 Corvette Factory Service Manuals you can read up on pulling the engine out completely.
Rebuilding it all at once would be a better option in my humble opinion.
Yeah I actually live in LA so no winter here in reality. So my mechanic did the test I don’t know how he did it but yeah 12-13% is very good I’m deciding to do a full engine rebuild. I’ll take the block to a machine shop and have them do what’s necessary. And yeah with that amount of miles smarter to rebuild the thing. I was gonna ask do you guys have any suggestions on what pistons and connecting rods to use? Sadly I can’t do a lot of work not super handy in that regard.
Last coupke 350s I pulled apart with 200k still had cross hatching on the bores. It wouldn't surprise me a bit if it's still okay enough to go together with minor work. But you don't know until it's apart. That being said unless it's been neglected a refresh probably won't hurt. Get a shop you trust to look at and pull it apart. Explain to them to give you options on what they think it needs. Most places will give you a rebuild route and then what they feel needs to be done to get it back out there as well. Go from there. Otherwise it's a WAG. I personally can't speak for your engine as I'm sure no one else can until their hands are on it but it seems you're moving in a good direction.
I agree with the above posts. I purchased a 84 back in 2011 to restore. I did all the body work and paint first and a couple years later got into the engine and transmission.
I purchased a block and necessary components to build the engine. I did this because I really could not find out the true mileage on the engine. It was using oil and smoking. It cost more money this way but I have a great running motor now that will last me as long as I will drive it.
Go for the complete rebuild if you plan to keep the car and enjoy many miles of smiles in it.
I would start by replacing your valve seals. I had similar symptoms to yours on my stock 327/300 engine: My '67 coupe was blowing blue smoke upon start up and was using about a quart of oil every 6-700 miles. The #2 and #4 spark plugs would foul quickly, leading to loss of power. The car had an unstable idle that I thought was carb related. Replacing the fouled plugs would restore performance and idle quality, but only for as long as it took for the plugs to foul again. The engine had 91,400 miles and was completely rebuilt in 1990, including multi-angle valve grind and new valve guides. When rebuilt, the engine had 74,000 miles on it, and had traveled about 18,000 miles since being rebuilt.
It was suggested that the valve guides were worn, allowing oil to drip into the cylinder and foul the plugs. The fix would be to remove the cylinder heads and have them reconditioned with new valve guides etc. Not a cheap fix.
I decided to begin by replacing the valve seals. That fixed all the problems, and the car ran better than ever! The old umbrella seals had become rock-hard and several had disintegrated.
I suspect the internals of your engine are fine. Start by replacing the valve seals and see if this fixes your problem.
Here's an excerpt from a post I made about my valve seal replacement:
Originally Posted by Mr Fufu
UPDATE– Valve seal replacement
Some of you will recall my ongoing efforts to improve the performance of my ’67 coupe with 327/300 engine (factory A/C car).
I got my ’67 about six years ago. It ran well enough then, but soon I had trouble setting the timing because the I later learned the harmonic balancer had spun. Once that was fixed I moved onto sorting out the carburetion issues – leaking gas, stalling, hesitation, etc. I rebuilt the replacement Holley 1850-C that came on the car. That cured most of the issues, but I never liked how the fuel line to the carb had been cobbled together using rubber tubing. So, last year I bucked up $700 for a correct brand new Holley 3810 carb. The new carb really made a difference – no more leaks, or stalling when stopping sharply, along with better mid-range power.
However, I could not get the engine to idle smoothly, and vacuum at idle would fluctuate rapidly between 16-18” hg. I thought I must have a vacuum leak somewhere, but never found it.
Last summer I noticed the engine starting to use more oil. I’d also see blue smoke upon cold start. Two of the 8 plugs would regularly foul with oil. Replacing the bad plugs would restore performance, but only for a few hundred miles until they fouled again. This pointed to worn valve guides or valve seals as the culprit.
Yesterday I had a shop replace the valve seals with the heads on the engine. The job took about 5 hours. The only thing found on the valve stems were black hard plastic umbrella seals! Of the 16 umbrellas, 9 were intact and 3 were missing their top portion. Four umbrellas had disintegrated, with smaller pieces lying about the lifter gallery. There were no O-rings installed on the valve stems.
The mechanic cleaned out the broken umbrella pieces and installed FelPro SS-5112 ‘O’-rings and FelPro SS-10058 umbrella seals, this as recommended by Joe Fisher in his excellent photographed procedure (Thanks Joe!)
Result – no more blue smoke on startup, a steady idle with 19” hg of vacuum at idle, and smoother power delivery on acceleration! I’m thrilled that my Sting Ray is finally performing as a Corvette should!
Thanks go out to everyone who supported me with advice and direction. You guys are the best!
People should really get into the habit of looking at the date of the posts they are responding to. I would more that suspect that since this post is over 14 months old, a solution should have been worked out.
Folks should also turn off continuous scroll and related threads.
Also it has been six months since the OP was active on the forum
C4 engine rebuild
