Just got back from my corvette mechanic this afternoon. He listened to knocking I have been hearing from the top or bottom of the engine. He determined the knock is coming from the bottom and he said they can pull the oil pan to look for issues, but with 100,000 miles on the car it would probably be more economical and money well spent to do a complete rebuild with an upgraded cam and higher 9.5 to 1 compression pistons. Going this route I am looking at around 5K complete job.

What has been your experiences for similar, rebuild or replacement? Should I be doing more upgrades to the original engine if I go the rebuild route? It still has the CCC installed, has plenty of power and runs pretty good, except for the internal knocking.

Or should I just go for a new crate engine and keep the original on the side?

I am kind of leaning towards keeping the original since I have been replacing parts over the last several months since purchasing to bring it back to original as possible. But if I do, should I look at more upgrades besides the CAM and pistons?

Another option is to just do the work myself, but my mechanic warranties all of his work for 12 months / 12,000 miles and is very reasonable on his labor.

Thanks

 

GM warrantees their work also, and 5 grand puts a lot more pep/dependability under the hood.

 

I completely rebuilt/upgraded my numbers matching 78 L-82 4 speed spring 2014. I had the bottom end done by a reputable engine builder with new JE forged Racing pistons/rings, reconditioned the forged L-82 connecting rods/L-82 Forged crank, new bearing, oil pump etc. I did the top end-roller cam?AFR heads/reused the L-82 aluminum in take etc…$6K with me doing much of the work and new clutch, motor mounts etc.

If you want to keep the OEM L-81 engine have some machine work done professionally and do as much as you can yourself. If originality is not an issue (which I think it is), crate engine but crate engines from GM are expensive and generally will not make the power of my L-82 355 without bigger $. Cheaper engines will make decent power but not necessarily use the best quality parts…they can't for $3,500. Depends what you want…

 

If you want to keep the OE block and are willing to spend $5 grand why not go with a 383 rotating assembly? Personally I would put the motor on a engine stand and find a 400 to rebuild with some better heads.

 

For that price I'd opt for a crate motor.

 

I have an 81 and pulled the original motor and put in one I had rebuilt years ago. I only went with that choice because I allready had the motor and it wasn't going to cost anything. If you went with a crate motor for the point of "Saving the original for someday" when that someday comes you would still need to rebuild it BK of the knock. You seem pretty into keeping your 81 original (something I kind of wish I did) and since based on this comment you made you feel a 190 HP stock motor has plenty of power you don't seem like a speed freak (this is not a dig, please don't take it that way), I vote for rebuilding the one you have. while you are at it maybe put in a mild cam and increase the compression and you will have a stock looking L81 with the CCC working and a little more power. Best of both worlds

 

A high quality GM crate motor will most likely cost more than your rebuilding of your L-81, even with the best quality parts like a roller cam, new forged quality pistons, and high quality AFR like heads. You can also buy a lesser quality crate motors (lots of them that will work) or rebuild you L-81 with better iron heads and flat tappet cam for a lot less money and still achieve your goal. I opted for the originality look with my L-82 355 going with the highest compression ratio I thought the engine could tolerate on pump gas (89 octane is no sweat with my 10.2:1 compression, you could go higher compression with 91/93 octane), roller cam-no one can see it, and AFR aluminum heads-yes you can see them, but not overtly noticeable) and the engine is a screamer with the same idle characteristic as the stock L-82 BUT with 425-450 Gross HP. You can easily make your L-81 into a 355/383 making gross HP matching most crate engines, more likely more HP...

 

I vote for a crate engine with the level of power you are looking for. the electronic carb can have the secondaries richened up to help the performance but i would leave it on the original engine in case you ever want to sell the car. personally it isn't worth the storage space to keep it.with a crate engine your mechanic can have you back on the road faster and with fewer hassles. waiting for some machine shops to get something done is like watching paint dry.

 

Thank you for all the advice and replies!

Well I have been doing a lot of research last night and today online, talking to online engine suppliers as well as reading over everyone's replies here on the forum and discussing with members in my local corvette club. I also spoke to one of my fellow gear heads at work today who said he has an engine hoist, rebuilt several engines and just pulled one from his truck. He said I can use his hoist, any tools I don't have and he would help me pull and install the engine and get me back on the road if I decide to do it myself.

So I called the local machine shop my mechanic was going to use to see what kind of deal I can get if I pull the engine myself, (this local machine shop was highly recommended and the largest in our area, used by most of the local repair shops and our club members). After talking to them they gave me a few more options and a decent price, rebuild as stock, rebuild with upgraded cam and 9.5:1 pistons to keep the CCC happy and gain about 50HP. Also found out they offer to pull and install. I could save about $2400.00 doing it myself though and they will offer a 2yr, 24,000 mile warranty (I don't put that much mileage on my main car let alone the cruiser). Or let them do it, get a 4yr 60,000 mile warranty and save about a grand over letting my mechanic do the work. Although my mechanic is pretty good about throwing in some extra work and installing parts at no additional cost and check things out for little to no charge.

As several of the forum members pointed out I really am not into pumping up the horse power and pushing the car over the top, not looking to changing out the tranny, rear end exhaust etc. and satisfied with just cruising around and having some decent horses under the hood, looking good and keeping it as close to stock as possible. So I am leaning at going with pulling the engine myself, let the machine shop rebuild the motor with a better CAM and higher compression pistons, while keeping the CCC installed and running things. Going this route I can gain the knowledge of working on the car, know how things were completed and keep the extra funds saved for additional replacement parts and goodies down the road.

I'll get back to the forum and let you know my decision and how things are progressing.

Pictures of my 81

 

Went to see the local precision machine shop manager today for a second opinion, he diagnosed the car in a few minutes after checking with a few tools. The number 3 piston is having problems, so it is time to start spinning wrenches and do some heavy lifting for a full rebuild. Talking over the plan I am probably going to go with the stronger cam, little bigger compression pistons, and have the crank balanced with possibly a new harmonic balancer. That should pump up the HP 50-60HP and still be a stock 81, using the CCC with more pep under the hood.

Now working on gathering up a few of my gearhead buddies to work on pulling the engine. I also plan on cleaning up the engine bay and repainting while the engine is out.

I could then work on a future project to take off the 2-1-2 exhaust and go true dual exhaust all the way back which should pump up the HP a little more.