Following along with Lars- My own engine build
 

So I posted that I wanted to build along with Lars and finally get my L79 clone build started. I am starting with the short block I pulled out of the Corvette I sold several years back. The previous owner went out of his way to get this engine built with the correct dates and had it restamped to match the VIN because the previous engine builder told him that his engine block was unusable. I had that block fixed and reinstalled it into the car...
But to this engine....

I disassembled it today and for being "fresh" I didn't like what I found. I started off checking the piston depth. It appears to have the same crappy 4 valve relief flat tops that the Lars engine had. I don't have any fancy engine building tools, But I brought the piston to TDC and used a flat edge along with feeler gauges to come up with .033 down in the hole. Probably not good for compression
https://cimg0.ibsrv.net/gimg/www.cor...22db13e001.jpg
https://cimg7.ibsrv.net/gimg/www.cor...06d2a67308.jpg
At first it appears I had a good starting point. It looks to have aftermarket rods along with maybe a good crank.

Next I pulled the cam... well tried to pull the cam. It wouldn't come out. It spun free but wouldn't come out. I finally had to use the sprocket along with a pry bar to start working it out. It finally came out, but the results don't look good. It has 4 really bad cam bearings , all worn to one side. The rear one still looks good.
https://cimg9.ibsrv.net/gimg/www.cor...e648f2a822.jpg
https://cimg5.ibsrv.net/gimg/www.cor...fd02654bed.jpg
I don't know what would cause this, hopefully just a bad install on the cam. The cam doesn't look bad, but that's only an eye view. I wasn't going to reuse it, It has some Isky Mega Cam 270 in it, The car never ran well, probably due to the low compression and oversized cam.

All the crank and rod bearings are worn, probably due to the metal from the cam. Going to send it to the machine shop to hopefully figure out what messed up the cam bearings. I would hate for the block to be bad.

The crank is already cut .010, but here is the bearing picture.
https://cimg0.ibsrv.net/gimg/www.cor...4c7ee21295.jpg

Good job on the teardown & inspection! Yes, you have the Sealed Power cast pistons. Those pistons ride .033" down in the bore, so your measurement is right on the money. Keep up the good attention to detail! :thumbs:

Lars

Although I couldn't tell from your pictures, the cam bearings may have had the oiling hole at the 6 o'clock position (position closest to the crank). The downward loading of the cam against the bearing oil hole will tend to block proper oiling of the cam bearings. To get proper oiling, the oil hole should be at the 2 or 3 o'clock position when facing the front of the engine (engine block right side up). This allows the formation of an oiling wedge to pull oil into the highly loaded lower portion of the bearing. (The circumferential groove in the cam bearing bore of the SBC allows placement of the bearing oil hole in any position.) For further information, see AERA TB 1996 (July 2002)

So, where did you find the oiling hole?

The second bearing back it looks like it is in the 6 oclock position. The front one, easiest to see of course, is at the 3oclock position, but there looks to be a small hole at 6. I can't really see the other ones.
https://cimg6.ibsrv.net/gimg/www.cor...72e3eb3a05.jpg
https://cimg9.ibsrv.net/gimg/www.cor...6c35b2736f.jpg

Thanks. I didn't know the specs, but seeing that the PO had the block decked to restamp it, you would think the pistons would be higher up.

I will see what you suggest for pistons. Right now I have a set of 882 Heads and a set of 461X heads. The 461X have been ported for a "race" engine I used to have, probably not what I want on this build. I was thinking of buying a set of aluminium heads for it, I remember seeing someone post abut a set that had no bolt holes on the front.

Yep. The first cam bearing has two holes - with one at about 3 o'clock, the other will be about 6 o'clock - so not much wear because the 3 o'clock is doing the job. However, the 2nd thru 4th bearings have a greater load, and if the hole is at 6 o'clock, they'll become badly worn.

With the first sbc I built, the machine shop that did the boring and honing put the holes at 6 o'clock - when I refreshed that build, there was a lot of wear on these bearings. With every sbc I've built since, I've installed my own cam bearings with the oiling hole at 2 - 3 o'clock and had no unusual wear.

From what I understand the problem with factory cam bearings is the factory blocks have the cam tunnel machined of course before the bearings go in and then again after the cam bearings are installed - yes machine the bearings. What I'm saying is the factory blocks trued up the bearings after installation with some type of bore/hone. But machine shops don't. Machine shops just knock the bearings in hoping the cam doesn't drag. Not much is written about this but I have read of plenty of camshaft bearing failures. My imagination tells me the spin the cam by hand is a safety check for this.

One of the block inaccuracies quirks I call it. Like how the factory drills out the oil galleys from both ends of the block - hoping they connect well enough. Well sometimes they don't.:(

I did the build with the Trick Flow heads and a roller cam. The engine had flat tops and were 25 thousandths in the hole. I also had a custom mild roller cam and the engine made 302 rwhp without headers. About 6 months after the install I descovered I had a cracked block. I then moved on to a Blueprint 383. I have no idea why the block cracked. The power increase with the heads and cam were very noticeable.

There's really no way to tell from the pics what destroyed the cam bearings. I'm not a real believer in the 6 o'clock theory. I do install mine at 4 o'clock but all big blocks, Fords, and numerous other engines, even the new Dart blocks, come with bearings that oil only at 6 o'clock which is why I know it's not a major concern. Im told that Chevy bored the front three bearings from the front then the block rotated on the fixture and they bored the rear 2. This has been an issue as not all are perfectly straight. In engine rebuilding we often had a problem with 4 being tight more so on big blocks.

Yea I can't see them and I can't tell what position the rears are in. I do remember that this engine had really high oil pressure from what I thought was the oil pump. But I reused that oil pump in the replacement engine :willy: and the oil pressure was normal.

I will get my engine hoist back tomorrow and remove it from the engine stand and knock out the cam plug and see what the rear one looks like.

Piston choice will depend on the actual cc volume of the combustion chambers in the heads you decide to use. You'll need to measure them accurately. If you use iron heads, you'll want to limit compression ratio to about 10:1 if you want to be able to run the engine on premium pump gas. Your current compression ratio with those flat top pistons and .033 deck, assuming you have 64cc heads, is right at 9:1, which is a little low for best performance. If you use 64cc heads with a .051" head gasket, you can run a forged piston with a small 5cc dome to get comp ratio right at 10:1. This would run really well with the L79 cam. If you stay with a flat top piston and use a thin .027" gasket, you can get compression ratio up to about 9.4:1. :thumbs:

Lars

As the owner of a mostly stock (I think) '66 L79 with 65,000 miles on it, I'll be following along closely. :thumbs:
- Jeff

The Sealed Power 310P is a production Rebuilder piston not a performance piston.
Production rebuilders need parts that work in all blocks they receive. Some of these old engines have been rebuilt once or more and maybe decked a couple times before they come into the production shop.
For this reason all production aftermarket pistons are destroked by .020, this keeps the rebuilder out of trouble on piston deck issues.

Almost all performance pistons are not destroked so you don't lose .020 of stroke if you choose performance pistons.
Performance Pistons cost more than production pistons because the volume is much smaller.
The 310P used to sell for less than $5 to the production shops back in the 90's. $40 for a set of pistons? Many people bought these over the $250 set of forged pistons.

The 310P is a good piston, it works very well if used in the right engine. 4 valve releifs allow it to be used in the left or right bank, helped keep cost down.
All the other piston companies did the same thing because the piston volume all went to the major rebuilders.
You should know the deck height of your block and of your pistons before buying them so you get the right parts match.

I will have to CC those heads to make sure. I know the 461X heads were 2.02 valves and angle plugs. If they are 64CC's what do you think the compression would be with the .015 steel shim head gasket reusing those pistons I have now? (assuming of course I don't need to rebore it)

I know that block has been decked but I don't know how much. The PO had it decked and stamped to match his car. First I have to let the machine shop figure out why the cam bearings are so bad, If the block is messed up, I am back to square one.

:lurk:

461X heads had straight plugs and 1.94/1.50 valves. They were often refitted with the 2.02/1.60 valves and a chamber clearancing around the intake valve as was done with later SHP heads. The 461X heads had larger intake runner volume (~170cc) versus ~160cc for the 461 heads.

Well, That's embarrassing. I miss-marked the box I was keeping them. I remember them being angle plugs, so I pulled them out of the boxes and they are 292 castings.

So I read this several times and it reads like the block you have now is a restamped short block with a VIN of another corvette. Makes me think you are rebuilding it for the experience more so than a value adder to your car. In that case I wouldn't fall in love with it. Meaning if the block has expensive problems let it go and look for another.

On the other hand try as many machine shops as you need until you find one that you can work with. Some shops send all their machine work out and are nothing more than assembly shops. And there are excellent machine shops that still send some of the machine work out because they don't have that particular machine. Example the machine shop that did my cylinder heads couldn't regrind my crankshaft though they can polish and balance them. To sort them out you really need a quick shop tour. You need to sort out what the machine shop says they can do for that cam tunnel and those cam bearings.

Don't forget that when you deck the block (0.030") you will have to mill the intake but at different amounts on the sides and a different amount on the ends.

Good luck.

I am not in love with this block and doing all this adds nothing to the value of my car. Seeing my car has the original engine still in it, It will probably devalue my car. There is nothing wrong with my engine except it's just slow.....When I rebuilt it back in the early 2000's, I had it built to just the stock 300hp specs, if it even has that. I would just go buy a crate motor, but I want the original PVC set up and don't want valve covers with holes in them. I had this short block, which I honestly thought was good and just needed cleaning up, and a cam swap.. turns out that wasn't the case.

I have a machine shop I have used for years, they have done all the machining on my Chevelle engine. I trust them, their turnaround time sucks, but all good shops are busy. Good news is that I do have another block 3858180, so if this one sux I can start over. I am dropping it off in the morning, bad news is it will probably take them at least a couple of weeks to look at it.