Dealing with the 7M Block Crack

[TONY!]

There are a couple reasons why I am resurrecting this thread. One is because some people & I believe that cracks are a common occurrence with 7M blocks. Another is because there is not enough information on how to deal with these cracks and we do need more info about this “problem” and the various ways to deal with this crack. I have also been meaning to thank those that replied to my original thread that I started December 30, 2004.

Originally title: Can a block be welded?

Folks,
I have notice this crack some time ago and have wondered what to do for some time. I have tried to get another block, but then I would have to get different pistons. I have talked to four different machine shops about this and everyone says something different. Ranging from pin it, sleeve the coolant line, sleeve the bolt hole, & also leave it alone. I have also talked to two welders and they say different things as well. One says arc weld it, and the other says torch weld it with wet towels in the surrounding areas.
The first machine shop re-magnafluxed it for me and found that it is cracked only three threads deep.

I am seriously thinking about welding it. The machinists tell me no. One welder I am favoring tells me that he can easily fix it with an arc welder and that he will work slowly (on & off) as to not get the block hot and warp it. Nickel-moly is what would be coming out of the welder. Should I not be convinced? He says he has welded for 30years. I have money & time in this block and would really like to keep it. Does anyone know if ARC welding would warp this block/cylinders? Or if this would be a bad way to fix it? Or if the temperature changes of a running motor would irritate the fix because it would be a cast block & nickel material joining together. I don't think I will ever be 100% sure of any decision after every machinist/welder says something different.
What do you folks think?????
THANKS IN ADVANCE. I would feel better if I had your blessings with the welding, because I don't really know much about welding.

http://www.muggyweld.com/castiron.html

here is the video:http://www.muggyweld.com/cast1.html

or:

http://www.ssbtractor.com/wwwboard/v...=farm&msg=4463

or:

http://forum.doityourself.com/showthread.php?t=133821

lastly the best article:

http://mustangandfords.com/techartic...ild_390_block/

I think you can do it without a hitch....just get a good welder, good welding equipment ( as above noted) and make sure you penitrate well with the weld.

good luck

Im a welder by profession.
In this case, this is what I would do:
-Sleeve and heli coil the bolt hole (redundant)
-Sleeve the water jacket

WELDING THE BEAST:
If you choose to weld the crack, you will have warping issues to deal with. Not to mention, cast iron in large qty's (blocks) like to be preheated. If you don't they tend (not always) to develop micro fine cracks after welding. You will have one crack before, and about 10,000 microscopic ones later. Cast any thing (iron in this case) likes to have cracks just not on the surface, but cracks that run DEEP. So you weld the top of it. Who's to say that further on down the road it doesn't resurface because the crack was deeper than previously thought? If you tig the crack: grind it out with a diamond bur cutter. Clean the surrounding area as best as possible. I have had the best luck with rods that have a high concentration of nickel and silicon (not silicone as in boobies). My best performing rod for cast iron / crack resistance is actually made for welding 316 stainless steel!

Your other option would be to have it brazed. I do not recommend this although alot of old timers from back in the day would.

And Simann, penetration on that large of a cast iron weld without something over 200+amps is almost next to impossible without some sort of preheating. Penetration in the form of "soldering" or brazing is also next to impossible without some sort of preheating.

Just my $.02.

Again, I would sleeve the water jacket, and heli-coil the bolt hole. Its cheaper, and quicker. Plus, you won't have to worry about getting the whole block remachined.

mdcmotorsports wrote:
Im a welder by profession.
In this case, this is what I would do:
-Sleeve and heli coil the bolt hole (redundant)
-Sleeve the water jacket

Agreed. Welding is generally more trouble than it is worth when working with cast iron.

Following MDC's advice will fix the problem with minimal hassles in the future.

Compare:
My tig weld (still has held up through 10,xxx miles)


Muggy weld's cast iron weld:

Now granted that welds dont' always have to be pretty to be strong. This is just to show you what a stainless rod, a good tig welder, and some patience will do.

I'm gonna have to say that the sleeving option sounds best to me, judging by the content of this thread so far.

Mine is cracked in the same place. It was like that over a year ago when I put a stock type HG in and last week when I put a MHG in as the stock type one was starting to go. My HG was going on #6 on the exhasut side. Same as the the original. I didn't have an issue with it loosing head bolt tension or leaking from the crack. I wouldn't worry about it. Nissan L motors tend to crack between the In and Ex seats on the head too, I have run those also. If you were to weld it I would think it would be hard to drill and tap it as it would be harder than the base metal.

Mine is cracked in the same place. It was like that over a year ago when I put a stock type HG in and last week when I put a MHG in as the stock type one was starting to go. My HG was going on #6 on the exhasut side. Same as the the original. I didn't have an issue with it loosing head bolt tension or leaking from the crack. I wouldn't worry about it. Nissan L motors tend to crack between the In and Ex seats on the head too, I have run those also. If you were to weld it I would think it would be hard to drill and tap it as it would be harder than the base metal.

See my posts here: http://supraforums.com/forum/showthr...ighlight=crack

Thanks for the replies everyone.

Instead of spending money on the sleeve option or continuing research to determine this crack would not lead to an actual problem (vs. a speculated problem), I had the rare opportunity to buy a short block locally for only $80 that did not need oversized pistons.

However I still want to share what I found out about different methods since I did spend time researching to some degree and have heard a few propositions on how to deal with this as follows.

WELDING
I really wanted to get the crack welded thinking it will be finished then. I asked three different welders on how they would do it. Being that they told me they would ALL weld it DIFFERENTLY than each other, it made me realize that there was not one uniform & best way to do it, & that made me wonder. Maybe if all of them could agree on one procedure & not say other welding procedures won't work, it would have been more convincing to me. The one thing they had in common of course is that they would U-groove the crack to its depth & then fill it in. The biggest risk of welding is creating more cracks (as stated by MDCmotorsports), so it seems to be a very tricky operation. The two welding methods that were suggested to me that caught my interests were ARC welding by a welder of thirty years experience and spray welding by one of the most regarded local machinist. The machinist said his way was the best welding method but not the best method overall. All of the machinists did not favor welding as the best way to deal with this either. If you were to have it welded, it would be necessary to have the block put in an oven before and after the welding to allow for slower temperature changes, which makes it less likely to crack the block.

PINNING
I read about pinning the block, three machinists mentioned that to me. In my understanding (or lack of), I did not like this method because it did not address the possibility of the crack still spreading downwards. I know it would stop speculated leaking issues, but I just don’t understand how it stops the crack from spreading downwards (IF the crack would continue downwards, that is).

SLEEVES
Using a sleeve was one of the favored methods but I heard different opinions on which hole should be sleeved (bolt hole vs. water jacket). To me, I was not sure if the crack would continue to spread downwards, so I did not know what to think of that, other than hope that it won't. Also this does not address the possibility of coolant possibly seeping along the surface of the deck (unless the sleeve was used in the water jacket vs. the bolt hole). IF deck surface leakage was a legitimate concern at all, I would be willing to speculate that it would be more for a MHG than a composite one.

LEAVE IT ALONE BUT USE FIPG AROUND BOLT HOLE
Out of 5 machine shops I asked, three actually told me not to worry about it & that other motors have had the same situation without a problem. The two that looked at it funny seemed to be the least informed & seemed to have less overall knowledge or business for that matter. What the most regarded machinists in my area suggested was to use studs & to put FIPG around the stud that goes into that one bolt hole (just as ma71supraturbo did).
All of the machinists told me that even with the crack, I could still easily torque to 80ft/lbs & that would not be a problem, much to my surprise.

From what I have heard from two machinists & lzalusky (a fellow member who has also been told the same by his machinist), this type of crack is very common on Chevy 400 blocks. There have been more cases with those 400 blocks and what they seem to do is to just go forward without welding, pinning, sleeving, or any other procedure other than using FIPG to seal the crack (if that even). People or machinists might use those blocks as a reference for this issue. Only by looking over the cases of these cracks on 7Ms and 400s can you really separate speculated problems vs. actual problems (if any). The people that I know who have used these blocks regardless of the crack don’t seem to be having any problems so far.


If there were more cases of 7M’s with MHGs that are doing fine, I would have not bought another short block. I could have spent a little more time in research, but time is money too so I left for that reason. I am not throwing out my first block. I am still not convinced that it is bad just yet. I am pretty sure it would work fine for a composite type gasket. Maybe I’ll build with that if something goes seriously wrong with the first engine. In the meanwhile, maybe time will give me more information on this matter if others realize that they have the same crack and don’t have any problems from it…and if they speak up on the forums.

So far though, no one has ever said that this type of crack has ever given them an actual problem from a build. Ma71supraturbo, lzalusky, jjh, & I will tell you that there are many 7M powered Supras running around out there that have the same crack without their owners knowing about it. And SO FAR, NO ACTUAL PROBLEMS HAVE BEEN POSTED.

Feel free to add to this thread but keep in mind that there are other threads for speculation with little basis. We need more usable information from actual experiences, which is why this original thread (with the posts I resurrected) IS the best so far. For those who may not be able to easily access another block or who have money in theirs and will not get another block, may want additional information on sleeves, pinning, welding, or to hear what will actually happen from actual cases.

I have been meaning to post my writings for a while but I have recently talked to the following members and here is what transpired:

Jjh & I chatted about a month ago in AIM and he told me that he was going with the pinning option. Three out of his three blocks have all had this crack.

MA71SupraTurbo was just telling me about a month ago in the chat room that most of the 7M blocks he has seen have the same crack I speak of. He stated that he bought four JDM motors and found them all to be cracked the same way. He went forward with one & has not had a problem since. “So far so good,” is what he replied when I asked him, “never a problem?”

Lzalusky just happened by chance to PM and ask me what I did with my block a couple of weeks ago. I also asked him the same question and he told me he will also be building with a block with the same crack. He was telling me that if he got another block, it would just crack anyways.

Btw, I have much time off at during work so don't think this was done on my own time. heh

[ma71supraturbo]

For what it's worth, I have NEVER seen a 7m block that has been machined that did not have at least one crack. Two of them did not have this crack apparent prior to machining... My block has 1, in the exact location pictured (which, by the way, is the best picture I've seen of it yet -- my crummy camera's flash just made it impossible to see with the glare on the fresh block surface). The other blocks I've seen either had that one, or 3 (with two cracks in the surrounding holes).

2 diffs, 2 turbos, and 3 transmissions later -- the crack & MHG are doing fine...

My pic (can't see the crack because of the flash, but its hairline just like the one above and is the middle of the two sharpie marks): http://www.geocities.com/ma71supratu...hinedblock.jpg

[Adjuster]

Out of the 4 engine's in my car, so far, no cracks. (Knock on wood, and never on a rod.. LOL)

I'd go with some sealant, and leave it alone. (Using head studs of course.)

Later.

[drjonez]

i've never seen a 7M block w/cracks....

[suprra_girl]

now you have :-p

i haven't heard of this as common either... but thanks for a good load up on info

[Allan_MA70]

only other time i have seen cracks like that is when someone didnt clean the bolt holes out!

[drjonez]

i'd suspect that the cracks stem from the holes not being countersunk after machining....

[outofstep]

This isn't even close to a "very common problem," you're just going to confuse noobs and start bad rumors. In 5 years of interwebbing I have never seen a cracked 7M block or even heard of it happening.

[drjonez]

[ma71supraturbo]

Show me a close-up picture like the one Tony posted of the middle head bolt/oil galley hole of a machined, non-cracked block. Until then, 7 out of 7 blocks (from different machine shops) is hard to dispute IMHO. I could be very unlucky, but more likely is that most people don't look super closely at their blocks?