How far will a 6.2L bore?

[restoguy]

How far can a 6.2 block be safely bored? Can I bore it to stock 6.5L specs? Got an old 6.2 sit'n around that needs rebuilt and I just as well make it a 6.5 if I can. Everything I have has the bigger engine in it anyway.

[john8662]

Depends on which 6.2 block it is.

If it's a block which has a casting number ending in '599, then yes, it will bore to 6.5.

If not, the only really safe (for all blocks) will be a .040" overbore.

[arveetek]

My own personal opinion is that ALL 6.2L blocks can be bored to 6.5L specs. My reasons:

(1) The 6.5L is the same engine as the 6.2L, with just a bigger BORE.

(2) The 6.5L develops cracks more often than the 6.2L....is this because of thinner cylinder walls? Hmmmm....

(3) The 599 block was just a TRANSITION block....the 6.2L was being phased out, and the 6.5L was being phased in. I have seen no concrete evidence that the 599 block has thicker cylinder walls than earlier 6.2L blocks.

(4) The Diesel Depot has an early non-599 6.2L block that they've bored out and installed stock 6.5L pistons. They've put a lot of miles on it with no problems.

I used to believe that the 6.2L couldn't be bored out to a 6.5L, but now I'm a firm believer that the 6.2L can be safely bored to 6.5L and larger bores.

I wish someone would cut out 6.2L and 6.5L cylinder walls and measure them so that we could put this question to rest once and for all!

Casey

[john8662]

This has been hashed out before, but no solution yet..

Check this thread out, especially what More Power had to say about an engine builder boring 6.2's to 6.5 and having cylinder bores crack.

Another Myth... (http://72.22.76.69/tdpforum/showthread.php?t=2762&highlight=boring)

I think I was supposed to cut a piece out of a block. Well the shop finally has some room to get to that block, so it's coming apart this weekend, and being cut by plasma torch at work the following week...

[dieseldummy]

I think I was supposed to cut up my 6.5 block too... I guess I'd better get with it now that I broke it loose and took it apart.

[john8662]

As per the linked thread I posted above, the feeler gauges were used in between the "jugs".

I'm wondering where I should take my sample.

Here is my block:

(7) (5) (3) (1)

(8) (6) (4) (2)

Should I take the chunk out here:

(6)<- (4) --- the side of the bore left or right (in the middle of the bore)

Or take it out of the topside of the bore (middle probably) or bottom side (middle as well)?

Where ya taking your sample Justin?

[dieseldummy]

I don't know where to take a sample at??? I'll give ya a ring so we both can do this the same for the sake of research.

[dieseldummy]

I ended up going for the #1 cyl first. Eventually I might do all but #4 since it's been sleeved, but only time will tell. I used an oxy/acetelene torch to make the cuts. As a result they are not the nicest, but it gets the job done. If only I had a band saw... I made the cut in the middle of the cylinder starting at the bottom. I took out a 1"x2" chunk first. I then cut from there up both sides cutting out chunks that were a little more than 1/4 the size of the cylinder. I then cut out the top piece. (not pictured)

With out adding the .040" that this block was bored out back to the number I came up with the cylinder wall is an average of .25" thick. I noted a high of .27" and a low of .23". This was all done with a digital caliper though. I'll either have to go to the machine shop or send them to John to be miced.

Here's a couple of pics of what I did.

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1160.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1172.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1174.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1177.jpg

If anyone has an old cracked 6.2 or 6.5 block laying around I'd ask that you do something similar so we can get an idea of what blocks have the good thick walls and which don't. Maybe anyone interested could contact myself or John through the private messaging here if we really want to continue looking into this.

On a side note, I was looking into the water jackets through the new hole I made in the block to see if I could tell where the bolts go from a set of splayed main caps. I noticed that it doesn't seem like there is much material where the bolts go at first glance. I need to further examine things after I get more iron cut out, but I'm curious how these diesel castings compare to a gas block in how much iron is down there.

[More Power]

Here's what I know about the boring (TIC) question....

1- GM's recommended maximum overbore is .030".
2- I've heard from an individual in South Africa and one in Australia (those guys don't have nearly the access we do to engine parts) who reported longitudinal splits in cyl walls after boring a 6.2 to std 6.5 (and I assume some number of miles thereafter).

Based on the above, I can't suggest boring a 6.2 to 6.5 specs, except in the case of the 599 blocks (which were bored either 6.2 or 6.5 in the 1992-1993 model years by GM). But, experimentation is fine with me.... Let us know how they do after having been on the road for a while. :)

Jim

[dieseldummy]

I guess I should have mentioned that the block I cut up is a '93 vintage '599. It was a 6.5 then it was bored .040" over. I agree with GM on only going .030" for many reasons.

[john8662]

Did some cutting...

First off, I did a rough mic of the cylinder bores by transferring the diameter from a telescoping gauge then to the micrometer. So it's not near as accurate (and falls victim to technique) as a dial gauge set up for bores, but we're gonna try...

I decided to do the center cylinders in the block, cylinders:

#4 = 4.0069
#6 = 4.0074
#3 = 4.0083
#5 = 4.0082

The block was bored out .030 as stamped on the block and the pistons were 75mm (.030).

Just a refresh on bore size here..

The Stock bore size for a 6.2 is 3.9774" (101.026 MM)

So, for my bored block, 3.9774" + .030" = 4.0074"

My measurments were close, and I'm sure that the engine had at least worn .001" during it's use, although it didn't have much of a detectable ridge ring, anyways...

So, I did some cutting at work finally!

#4 = .2799 .2798 (measurements are at opposite ends)
#6 = .2319 .2515 .2382 (took some of the side, verses bottom on this cut)

#3 = .2621 .2418
#5 = .2509 .2660

Hmm, the smallest I measured was .2319, so thats what I feel confortable numbers wise with..

The proof (images)!

http://members.cox.net/trialanderror/block/cy6.jpg

http://members.cox.net/trialanderror/block/cy35.jpg

http://members.cox.net/trialanderror/block/piecefront.jpg

http://members.cox.net/trialanderror/block/pieceback.jpg

I'm going to make a speculation, but I don't feel that the 6.5 is a bored out 6.2L... Lets do some more testing, I'm gonna need Justin's measurements and we'll see.

[Bnave95]

Then,we'll wonder what a 6.5 block would look like?

[dieseldummy]

I'm jealus John, your cuts are much nicer than mine...:D

[john8662]

UPDATE!!!

Going to make some kind of inconclusive conclusion to "how far will a 6.2 bore?"

:)

I received a box with some block cuttings from a 6.5 from Justin, so I got to do some measuring and thinking. Basically we want to see if we can squash the little rumor of whether you can bore a 660 cast 6.2 to 6.5 dimensions.

Here's another pic of Justin's 6.5 cuttings:



http://www.thedieselpageforums.com/photopost/data/506/medium/JustinsBlockCuttings.jpg


Ok, here are the measurements:

Large Piece

.2399" (bottom)
.2436" (bottom)
.2490" (side)
.2000" (side)

Small Piece

.1984" (bottom)
.1989" (bottom)
.2179" (side)
.2314" (side)

Looking at the above measurements it's easy to see that the smallest recording is .1984" thickness.

OK, just like we did above, let's review 6.5 bore dimensions.

Stock 6.5 bore dimensions are technically 4.0544" (102.981MM)

Note: we don't have any mic'ed dimensions prior to cutting for this block, so we're gonna wing it, I'd say that our error should be around ~.005"

Block was overbored .040"

So... 4.0544 + .040 = 4.0944"

Our 6.5L in question should have a 4.0944 bore with no wear and with the .004" piston to bore clearance.

Now for the fun...

Let's compare the cylinder bore casing outside diameter between the two engines so far.

'82 6.2L .030" '660

We'll take our calculated measurement for the bore inside diameter (4.0074") and add the thickness of the thinnest measurement recorded (.2319") doubled (casting on two sides right?).

4.0074" + (.2319" x 2) = 4.4712"

Estimated 4.4712" Total Diameter of the outside of the bore casting (what you normally can't see, besides viewing through a freeze plug hole).

'93 6.5L .040" '599

We'll take our calculated measurement for the bore inside diameter (4.0944") and add the thickness of the thinnest measurement recorded (.1984") doubled (casting on two sides right?).

4.0944" + (.1984" x 2) = 4.4912"

Estimated 4.4912" Total Diameter of the outside of the bore casting.

So...

6.2L IS ~4.4712"
6.5L IS ~4.4912"

What's the difference?

-------> .02" <--------

OR! .020" ironically..

According to these numbers, there IS a difference in cylinder thickness between a 6.2L (pre 599) and a 6.5L (at least a 599, others may be different).

But, if this difference THAT significant?

Check my math and logic here guys!

Couple more observations...

The measurements did make a range, depending on the position of the cast, whether it was on the opper part of the bore, the lower part of the bore, or next to another cylinder part of the bore (you know what I mean). I took the thinnest measurements mainly because I'm looking for the safety margin. The bores do seem to be thinner at the tops, which I really didn't get from my 6.2L cuttings... Hmm...

J

[dieseldummy]

One thing that I should ad is that the cyl to piston clearence on this block was more along the lines of .007". That will make some difference in the calculations I suppose. I'll let you take care of the math, makes my head hurt:o

[john8662]

One thing that I should ad is that the cyl to piston clearence on this block was more along the lines of .007". That will make some difference in the calculations I suppose. I'll let you take care of the math, makes my head hurt:o

Head hurt? I was thinking along those same lines!

So, basically we can say that the 6.5L block is (fudging a bit) nearly .030 thicker if you say that the bore clearance was .007, then factor in wear from HD use...

I'd be interested in cutting a STD bore 6.2 with cracked main webs or other abnormality, as well as a 6.5. I think I've got another cracked 6.2 to cut thats STD bore, but don't (hopefully) have a cracked 6.5 to cut (yet)...

[simon]

I ended up going for the #1 cyl first. Eventually I might do all but #4 since it's been sleeved, but only time will tell. I used an oxy/acetelene torch to make the cuts. As a result they are not the nicest, but it gets the job done. If only I had a band saw... I made the cut in the middle of the cylinder starting at the bottom. I took out a 1"x2" chunk first. I then cut from there up both sides cutting out chunks that were a little more than 1/4 the size of the cylinder. I then cut out the top piece. (not pictured)

With out adding the .040" that this block was bored out back to the number I came up with the cylinder wall is an average of .25" thick. I noted a high of .27" and a low of .23". This was all done with a digital caliper though. I'll either have to go to the machine shop or send them to John to be miced.

Here's a couple of pics of what I did.

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1160.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1172.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1174.jpg

http://img.photobucket.com/albums/v622/dieseldummy/DSCF1177.jpg

If anyone has an old cracked 6.2 or 6.5 block laying around I'd ask that you do something similar so we can get an idea of what blocks have the good thick walls and which don't. Maybe anyone interested could contact myself or John through the private messaging here if we really want to continue looking into this.

On a side note, I was looking into the water jackets through the new hole I made in the block to see if I could tell where the bolts go from a set of splayed main caps. I noticed that it doesn't seem like there is much material where the bolts go at first glance. I need to further examine things after I get more iron cut out, but I'm curious how these diesel castings compare to a gas block in how much iron is down there. Going back in time here, but did anyone had a chance to cut a block trough the pan rail to see where the best place is for splayed main bolts?

I felt trough a freeze plug hole , and did not think there was that much meat up at the panrail area. Kinda hard to figger out how deep to drill without going trough in the water jacket.
I would have cut a block apart myself if i could have found one in my area.

Thanks Simon

[john8662]

Got a good idea of how to section the block?

I don't think a cutting torch is a good choice here...

I've got three cracked blocks sitting around that I'd like do some experimenting with, if I had a way to cut it, then i'd go for it.

But you're right, there really isn't that much meat there for the splayed bolts, and you'll certainly run the risk of hitting the water jacket.

My splayed 6.5 fell victim to hitting the water jacket on a couple of holes.

J

[simon]

Got a good idea of how to section the block?

I don't think a cutting torch is a good choice here...

I've got three cracked blocks sitting around that I'd like do some experimenting with, if I had a way to cut it, then i'd go for it.

But you're right, there really isn't that much meat there for the splayed bolts, and you'll certainly run the risk of hitting the water jacket.

My splayed 6.5 fell victim to hitting the water jacket on a couple of holes.

JI think if you take a 7" angle grinder with a 1/8" cutoff blade and start 3" from 1 side of a mainweb and cut a groove under a angle towards the head, and then cut straight down right beside the web till the cuts meet .
you should be able to get a nice wedge out of there me think
you just need a real steady hand, and brace yourself good. it wil cut like butter. Maybe leave the last 1/4 inch sit , take the piece out with the hammer, prevents the piece from jamming the grinder if it breaks loose. is safer that way me thinks

[dieseldummy]

Cutting with an angle grinder kindof sounds like a suicide mission... A much better choice would be a band saw. If I had access to one I would have taken a cross-section of the block. There isn't much meat in the pan rail area for splayed mains. I guess there doesn't need to be since the idea behind splayed mains is just to spread the load out over the block more evenly. I'm still not certain it is worth it though...

[Robyn]

Just for the sake of argument.

I would be hard pressed to go past .75mm overbore on one of these blocks.

I had a 6.5 block sonic tested recently prior to a purchase. (That did not happen)
We found that generally what you are showing here is just about right on the money.

We did tests at 8 spots around the diameter and we did this in 1 inch steps starting at the bottom of the bore.

The scarry part was the little pockets that are present where the core must have been uneven.
We found one area on the upper 2 inches of a couple cylinders that had good thickness but then there would be a little pot hole if you will that was very thin.

The block in question was already .75 over and needed to go farther.
The basement was sound but I was very nervous about the bores.

If we had gone on out with it we would have possibly hit water in a couple spots and maybe had failures after it was running.

The seller insisted the block would go more but after doing the sonic I decided to pass on it.
I would have liked to cut the sucker open but the seller was adamant on selling it as a good block. (End of story)


I dont know if 6.2 blocks would be any heavier or have any more integrity in the cylinder wall thickness.

Regardless I would cap the plan to overbore any of these at .75mm

Far too much $$$ to find out down the road (No pun intended) that the sucker has issues.

Sonic testing is not cheap but I have a friend in the business that was also interested in the 6.2/6.5 block thickness so he did this one on the house.

I think we were just lucky to have found those pot holes because you could miss something like that real easy.

Every 45 degrees around the hole and do it on the inch starting at the bottom and work up.

Takes a bunch of time too.

Hope this offers some insight into this bag of worms.

Robyn

[simon]

Cutting with an angle grinder kindof sounds like a suicide mission... A much better choice would be a band saw. If I had access to one I would have taken a cross-section of the block. There isn't much meat in the pan rail area for splayed mains. I guess there doesn't need to be since the idea behind splayed mains is just to spread the load out over the block more evenly. I'm still not certain it is worth it though... Please explain [ suicide misson ] does the noise or the sparks scare you.

What is better, Trying and fail, or failing to try.

[dieseldummy]

The kickback factor is what scares me... there is a reason that stationary chop saws were invented. One wrong move and there is a good chance of injury. This is observation after spending a good amount of time running a big angle grinder. If I had a junk block laying around still I'd offer it up for someone else to try and cut up. John and I did our part in the cylinder wall thickness proof department... I'll let someone else do the pan rail thickness idea.

[simon]

The kickback factor is what scares me... there is a reason that stationary chop saws were invented. One wrong move and there is a good chance of injury. This is observation after spending a good amount of time running a big angle grinder. If I had a junk block laying around still I'd offer it up for someone else to try and cut up. John and I did our part in the cylinder wall thickness proof department... I'll let someone else do the pan rail thickness idea.OK, point taken, I'll have to find a block , then i'll do it

[simon]

Well it took a while looking for a block to cut open, did not find one so i decided to use my own web cracked 98 506 block.

against diesel dummy's and others advice i used a 7" x 1/8 zipdisc on a 7" angle grinder to cut a wedge out of the rail area adjacent to the center web. i started with a angle cut 2" out and 2" deep towards the web, and than straight down beside the web till within 1/8 of the angled groove, and pryed the pieceback and forth till it broke free. the whole operation took less than 2 min to do. piece of cake, nothing to be scared of, no kick back occurred.
but I am NO amateur with a grinder to start with.

thickness of the metal from the surface of the panrail till the waterjacket is minimum 1 3/16 on the inside to 1 1/4" against the outside of the block, wich leaves enough meat in my opinion to drill a hole 1" deep staight down or at an angle for the outerbolt of a splayed cap or full girdle. It baffles me wy in the world GM decided to put the outerbolt holes in the place they are.

I would put some pics on if i could find a way to do so, but for some reason they are to big and i can't get them smaller.

Simon

[86 CUCV]

After reading All of this valuable information I am wondering a bout the affect of core shift which may affect any block and any cyl wall.
If I want to go to a big bore I get the block ultra sound tested at a good shop
I do like where y'all are going here though as I am researching the rebuilding of my 85 CUCV original 6.2
and am looking for the biggest safe bore I can use safely

[More Power]

After reading All of this valuable information I am wondering a bout the affect of core shift which may affect any block and any cyl wall.
If I want to go to a big bore I get the block ultra sound tested at a good shop
I do like where y'all are going here though as I am researching the rebuilding of my 85 CUCV original 6.2
and am looking for the biggest safe bore I can use safely

Glad you brought that up. As I mentioned earlier in this thread, I had heard from a couple South African and Australian members who reported longitudinal splits in the cylinder walls after boring a pre-599 6.2 block to std 6.5 bore dimensions. I thought at the time, and still do, that a core shift during the casting process may explain this.

GM's maximum recommended overbore for either the 6.2 or 6.5 is 0.030", but most engine shops will be happy to do a 0.040" overbore, and you'll find a ready supply of 40-over pistons on the market. Personally, I'd look for another block, if at all possible, before going farther that 40. Jim