WernerGMHTP

iTrader: (12)

Hi all,

I just purchased a used block from a guy who said it was out of a 1999 Z28. Funny thing is, it doesn't have the larger machined passage between the lifter galleys in the back of the block. In other words, it looks like a 1997-98 block from the back.

I've heard some early 1999 blocks were like this, so I'm willing to accept that this is probably an early 1999 block. But what I'm completely unclear on is whether these early 1999 blocks had the thicker cylinder liners that allowed them to tolerate a more substantial hone like the later ones. The casting number on this block is 12562174. Any help would be greatly appreciated.

Thanks,

Chris

oange ss

iTrader: (50)

where did you get that number from ?

WernerGMHTP

iTrader: (12)

That number came from the back of the block, driver's side, just like as shown here (different number of course):

http://www.gmhightechperformance.com.../photo_13.html

oange ss

iTrader: (50)

cant find any info on that number...the xxxxx378 is the newer LS1 block

WernerGMHTP

iTrader: (12)

OK folks well tell me this: assuming this block DOES have the same thinner iron cylinder liners as the earlier 97-98 blocks, where/when has GM officially said anything about the max recommended overhone being less for these blocks than it is for newer blocks? I've heard people say that "GM recommends only honing these blocks 0.004", but have no idea where this information came from.

The reason I say this is that I have in my hands an official "5.7L (LS1) Specialized Engine Repair" manual published by GM Service Technology Group in 1998. It's on loan from GM Powertrain, so it's 100% legit and official. It clearly states that the max recommended hone for the LS1 block is 0.254mm (0.010 in.). Since no later blocks were in existence at the time this manual was published, this spec must apply to the 1997-1998 blocks. Did GM later change their minds about this spec, or something?

BTW, I'm not trying to dispute the fact that the newer blocks are better, etc... I'm just trying to perform a stock rebuild here and could care less if the engine can support 500+ hp.

Any help would really set my mind at ease. Thanks in advance!

brad8266

iTrader: (23)

Appears to be a 99 to me.

brad8266

iTrader: (23)

Just take it out to 3.905 or slightly under that. thats what most aftermarket pistons are anyway.

WernerGMHTP

iTrader: (12)

Unfortunately I'm not using an aftermarket piston. I'm using a stock replacement hypereutectic piston straight out of the GMPP catalog, and they only make it in stock bore and 0.010 oversize. One would assume that if some blocks couldn't go up to 0.010 over, GMPP would offer a piston only 0.005 over or so - but they don't.

Can anyone verify this reduced GM oversize spec for the earlier blocks???

brad8266

iTrader: (23)

Can you just get away with a quick hone on the cylinder instead of a bore job?

Steve Bryant

iTrader: (1)

Chris,
Engine Builder Magazine's website has a wealth of information of the type that you are seeking. Specifically, look at this article http://www.babcox.com/editorial/ar/eb040538.htm. Also, go to http://www.engine-builder.com/ then click "Search Back Issues" and type in Gen III. Like GMHTP Magazine and the other Primedia Publications, Babcox Publications' Engine Builder Magazine is one of the best of it's type.

As I recall, you are mainly rebuilding this engine for the experience and not as a mega performer. If I were you, I would take the block to a machine shop and have the mains checked for alignment and ID being within tolerance. Then, install new cam bearings, have the decks checked for flatness (block and heads) and check the cylinders for bore, taper, etc. You might be able to simply have them hone the cylinders a couple of thousandths and re-use the existing pistons with new rings. Then, disassemble and check the valve seats and valves at the face for wear as well as valve stem/valve guide for wear. If all is OK, you could just hand lap the valves or maybe have a three angle valve job done if you want. You could also blend the bowls of the intake and exhaust ports for the experience.

These are just some budget conserving thoughts for you to consider. My approach would allow you to get the experience and have a very serviceable engine. This way, the learning experience can be useful yet affordable.

All my best,

Steve

oange ss

iTrader: (50)

pull the rear cover off and look at the cam rear oil galley, if it just has 2 holes it's a 97-98 block, if it has 2 holes and a "loop" config, then it's a 99+

oange ss

iTrader: (50)

according to Mortec, its a 98 block...

WernerGMHTP

iTrader: (12)

It's a strange bird... the block is stamped "99" right onto the front, and the partial vehicle VIN etched into the block verifies it's from a 1999 Chevrolet. Yet is has no "loop" config in the back, just the two lifter oil galleys only connected by a small groove in the rear cover.

To Steve: thanks for the complements on GMHTP as well as those web site links, I actually already found them a while back. The issue I am having is verified right in that babcox/enginebuilder.com article by Doug Anderson. It says right in there:

"GM says you shouldn't bore the cylinders on the '97-'98 blocks more than .004 and recommends not boring the '99 and later ones more than .010"

Assuming that my block is so early in the 1999 production run that it really should be considered a "1998," I would love to know where Mr. Anderson got this GM info on the .004 limit - it directly contradicts what I have here in my official GM/ASE book (.010 all years). I trust him, but I'd like to know if anyone else has heard this officially stated by GM just to try and clear up the discrepancy...

Steve Bryant

iTrader: (1)

Chris,
If you want, give Doug a call. I'm sure that he researched the article just like you or I would on a writing project. However, even with the best of intentions, it's easy to be misinformed or mistaken. Also, it wouldn't surprise me if some of the "official" GM information is contradictory (although I'll have to say that in general their maintenance manuals, etc. are first rate).

I work as an avionics engineer for a general aviation manufacturer. Sometimes (frequently really) we have changes that do not coincide with annual "model year" changes. We have "serial effectivities" where one configuration runs through serial number X and the next configuration begins at serial number Y. Sometimes, we have more than one approved source for a part (form, fit and function are the same) so you could get parts that vary for this reason.

I believe that similar situations occur with all manufacturers (including GM). For instance, look at the number of head castings that are being discovered for the L92/L76 cylinder heads. This has been the case in the past on other LS series components. You may have one of the early '99 model year engines with the older style of block.

Now, back to the bore diameter. Are your cylinders scored? I suspect that the four thousands is really conservative. If you bored/honed the cylinders only .010", that is only .005" on each side. Surely the steel liners are thick enough to handle this, but then again, maybe not. Maybe a sonic check would tell the story. I'm building a 408 now with a used cast iron block and I had a sonic check done first. My .030" bore increase exceeds GM's recommendation of .020". However, on the thrust sides of the cylinders, I have enough meat left. I know that this is not an apples to apples comparison . . . cast iron versus a steel liner in an aluminum sleeve. However, I am cautiously and judiciously exceeding their recommendation by .010".

Keep us posted!

Steve

s346k

iTrader: (4)

99s don't have the updated oil return.

do some research.

00 is the first year for block revision.

WernerGMHTP

iTrader: (12)

Steve,

I actually emailed Doug Anderson last night, hopefully he can help shed some light on the subject.

Good point on the production variation. I'm an ME myself, and of course these kinds of things are to be expected, especially with a company as big as GM! Mid-model-year changeovers are fairly common from what I've seen too, and who's going to, for example, throw out the last 900 blocks cast and unused in 1998 just so all 1999 model cars get the benefits of the model year update? (I should still note that my block says "99" right on it, but that's besides the point at this juncture).

It just seems to me that if GM was training their techs with a book that states a max overhone value for all LS1s, they'd run it conservative, i.e., .004 to match up with the thinner castings that came through. Saying it's .010 for all blocks when really that's only true for some would be a bad move... the only thing I'm worried about is that GM didn't KNOW that some blocks couldn't tolerate a full .010 until after the manual I have was published (in 1998).

Your suggestion on simply mic'ing the cylinder walls and checking it out for myself is exactly what I had figured on doing. Heck, I'd have done it anyway even if GM guaranteed a .010 spec was OK no matter what. But I'd still like to know what GM's official recommendations are, as I'm going to be publishing these specs in some work of my own - and I refuse to steer anyone in the wrong direction and throw out what could be a perfectly good 99-and-earlier block. Hopefully Mr. Anderson can shed some light on the subject...

Thanks again and best of luck with the 408!

Chris

crzhrs

iTrader: (11)

Hey Chris, Did you ever find out any more info on this block? I have one myself now and am very curious if it can be bored .010 as well. I have done alot of searching and can not come up with a definitive answer.

bjamick

iTrader: (31)

My block has a big 99 on the back of it.. So I figured all LSX blocks have the year right on the back of them?? Guess not though.

WernerGMHTP

iTrader: (12)

Brian,

Unfortunately, no... never was able to come up with a definitive answer. I did end up going .010 over with my block, but it turned out the block had been cracked around one of the cylinder liners (slipped the machinist's eye) so I couldn't use it. This apparently happened before any machine work, while the engine was still running.

That said, it's probably just a result of my own experience with this one block, but I'm now of the opinion that these earlier castings are a little more frail than the later ones in many regards, and while not inappropriate to use per se, should probably be avoided if you're going big cubes, forced induction, etc. IMO, I'd avoid going .010 over on one of these blocks if at all possible, but if you do, make sure a competent machinist gives you his/her professional opinion on doing that first.

Best of luck!

Chris

crzhrs

iTrader: (11)

Thanks for the info Chris. I'm afraid no one is gonna have a definte answer for this block being that it is an oddball of sorts. I'm going twin turbo so I think I'll just pick up another block.