Splayed Main Caps

[opto]

The common procedure when installing SPM seems to be to thread in a cut bolt in the unused holes.

How about welding the holes up all the way from the bottom??

[DmaxMaverick]

Bad idea. Cast iron isn't friendly with welding under the best conditions. You'd have to bake the entire block overnight (or longer) to get it up to temp for a good weld that won't destroy what integrity the main webs have left. It could also leave you with a "softened" block, leaving it prone to many other issues you don't currently face. The hole should be "filled", and a bolt seems to be the best solution. I would use a "soft" bolt (as opposed to hardened, a grade 5 rather than a grade 8), to allow the bolt to go with expansion/contraction, rather than create a resistance, which could result in additional stress. The best advice I can offer is to follow the advice of those who do this frequently. JK, Ronniejoe, etc.

[opto]

so you think that even if the welding is done by the book it's a bad idea and will weaken rather than strengthen

You can also put it this way - is there any record of block cracks after SMC have been installed, if so it's really nothing to consider at all

[DmaxMaverick]

"By the book" means heating the entire block to around 800 - 1000°F, IIRC. Local heat causes localized heat stress in cast iron, as it does not heat evenly when you weld just one spot. Like pouring hot water on a frozen window. The rapid change of heat on the outer surface causes the glass to break due to the stress difference with the inner surface. I believe welding the holes will make the situation worse, no matter how you do it. I may be wrong, but you'd have to show me the science or results to convince me.

I don't know if splayed mains reduces block cracking. Some say it does, other say it doesn't. Theoretically, it should improve conditions. However, splayed blocks have cracked. It's hard to say at what time the cracking began, before or after the procedure. I think much depends on the condition of the block you start with. Just because you don't find cracks doesn't mean it isn't prone to it. There are other factors to consider, as well. Also, where is the point of diminished returns? In the end, it may not be worth it, depending on your application.

[ronniejoe]

However, splayed blocks have cracked.

Can you show some evidence to support this claim? I've not seen or heard of any cracking after application of the splayed main caps. The splayed caps stiffen the bottom end of the block and reduce the stress in the main web area.

There is one case of a cracked block that was repaired with the Lock-n-Stitch method then had splayed caps installed. It is running fine after six years and several thousand miles. If splayed mains don't fix the cracking problem, this one should be done already.

[Robyn]

I agree with Maverick
Welding up a block is a very bad plan under the best of conditions.

The best techniques with the best equipment done by the most qualified welder still fall short of perfection.

Once the block is brought up to temp any stresses that have accumulated over time due to the normal duty cycle are going to release and that block is gonna get real squirelly.
The mainline could very well go all over as well as all the other dimensions that are critical.

If I were to do this I would use a soft bolt of the proper size and thread pitch and locktite it into the outer hole.
Then the new caps could be fitted and the new angled outer hole drilled and tapped.

A local shop has one of the "Aftermarket" blocks with two (2) bolt center caps and it was recently finished up and installed in a rig.

I am trying to follow its history from this point on to see how well it does.

Personally I thinik it probably will do well as there is not the weak spot or the stress riser to help initiate the cracks in the first place.

I also know of a 6.5 that was rebuilt with two webs cracked and they let it go.
Its got 3 years on it now and its still going. :eek:

I would not waste the time or $$$ on a cracked 6.5 but thats my opinion.

Now for whatever its worth. IMHO if you have a 6.5 block that is well seasoned (200k) and NOT cracked, it probably is not going to.

After so many duty cycles the iron settles in and if there are no stress risers left to let go then its probably good forever.

I am still of the opinion that there is something going on with these engines that has not been fully discovered yet.

I believe that a good stress analysis program could sort this out given some time and snooping around.

I am also of the opinion that some of the cast cranks are getting hinky and doing wierd stuff under load that is causing the block undo stress that results in the cracking.

I have pointed the finger at the crank for a long time.. Now lets say that the iron crank was absolutely the ticket and could bnot be an issue, GEP/AMG would not spend the BUCKO's to build forged steel units. The fact that they have just increases my belief that the iron cranks are to tweeky and part of the issue.

All the other engines such as the Mighty PSD and the Cummins use Forged steel shafts.

Iron makes a good block but the crank needs to be good steel.

I looked into a billet crank buit the cost was prohibitive ($2800)

I have also torn down some 6.5's that had cracked mains and withn this I found unusual wear patterns on the center main bearings.
Now I cant tell you which came first the cracked webs or the unusual wear on the shells.
The web cracks were not all that pronounced so I will venture that the crank was goofy and doing the watoosy in the bearings.

Just some observations

Robyn

[DmaxMaverick]

Can you show some evidence to support this claim? I've not seen or heard of any cracking after application of the splayed main caps. The splayed caps stiffen the bottom end of the block and reduce the stress in the main web area.

There is one case of a cracked block that was repaired with the Lock-n-Stitch method then had splayed caps installed. It is running fine after six years and several thousand miles. If splayed mains don't fix the cracking problem, this one should be done already.

I don't know of any 6.5 blocks that have cracked after splayed mains. That doesn't mean they can't or haven't. However, splayed mains is not a new technology, and not unique to 6.5L Diesel engines. If it hasn't happened, it just hasn't happened yet. That is not to say it doesn't improve durability.

A weld repair is much different than filling a deep threaded hole. Much would depend on where and why it needed repair. The bolt holes would be better left alone, or with a bolt.