Isuzu SUV Forum banner
1 - 20 of 29 Posts

·
Registered
Joined
·
6,257 Posts
Discussion Starter · #1 ·
I'm just curious to why anyone would weld the journals to a bad crank if it's such a bad option? I've had machinists tell me it is an option, but also told me not to do it. Anyone who's had anything to say about rebuilding engines has probably told me the same thing. Was this something that used to be done in the old days more reliably due to a different metal composition? Or are machinists skipping out on something that makes it less reliable like heat treating? I'm just curious, because the act of welding a crankshaft journal is something I hear quite often yet it seems like no one advises it so I would have to assume that to some extent it remains popular or at one point was a common thing other wise people would not talk about it. Anyone with any knowledge on this?
 

·
Registered
Joined
·
2,897 Posts
Here's what our take was on welding a crankshaft. We used a spray welder (Eutectic) to weld a crank but we only welded thrust surfaces and only on a crank that was not easily obtained. Part of that equation I'm sure was cost, it just didn't make sense to weld a common crankshaft. We seldom welded any and the ones welded were generally tractor cranks.
One exception and it was more or less an experiment a guy wanted to undertake stroking a 2 cylinder John Deere crank for his "stock" pulling tractor. On that one we added material then ground the crank with additional stroke.
Given any choice I'd just as soon not have a welded crank. I do think a lot of the negative is likely brought on by someone that doesn't know how or when to do it and doesn't have the proper experience or technique. Likely also doesn't understand the limitations but I'd still avoid a welded crank if possible.
 

·
Registered
Joined
·
13,615 Posts
The big difference is material... Cast cranks are soft and more likely to warp and loose strength when they've been welded. I had a diesel crank welded up that I've yet to use (build the motor) diesels are low rpm to, so that helps. Performance grade cranks are steel cast alloy ... For years Volkswagen cranks have been welded and reground for big strocker engine builds. When I built my 2086 I purchased a cast pre made strocker crank though. I keep hearing that you can't turn the 3.5 cranks for fear of breakage, let alone weld them. Must not be very good material (sigh)... As far as the 3.2 cranks I have no idea but probly the same cenerio... If you ever get a chance to pickup and feel the same model crank in a cast iron and forged steel the weight difference is a lot. So much denser material... Race cranks can be welded to save expense, the new processes of weld build up probly doesn't faze them... I wish we had a steel crank available for the isuzu's ... Are the 2.6's steel ???
 

·
Registered
Joined
·
3,934 Posts
I had my 3.2 crank welded and it cracked and broke. Never again.
 

·
Registered
Joined
·
1,906 Posts
Like has been posted the best time to do welding on a crank is when there hard to come by. The 29 Stutz I had at school If it needed crank work we were going to do welding on because have you priced a crank for a 29 stutz 6 cylinder lately. Have fun finding one lol. So it really depends on when and if you can find the part and if its easy and cheap to get theres no point in taking the risk because you do take a big risk welding on something like a crank and weaking it.
 

·
Registered
Joined
·
6,257 Posts
Discussion Starter · #6 ·
out of curiosity, for cast cranks where welding might weaken it, wouldnt heat treating it restrengthen it? OR does it not strengthen it enough to make it worth the extra cost?
 

·
Registered
Joined
·
13,615 Posts
That's a good idea. Typicle cast poured cranks can have air pockets in them from impurities. One of my 350 cranks had been turned and the rear main journal had a tiny pocket exposed. My brother explained that to me. He was a machinest for 19 years. Made things nice for building engines. Anyway heat treat most likely would warp that cheap of a crank. I've had diesel cranks turned and re- heat treated. It was an old turbo'd international dozer. Some time later the crank did break. Over 4 grand for that crank alone, so I repowered it with a 4bt cummins... The Volkswagen cranks where steel forged from the factory so super high quality. And I had to see it to believe it, about the welding and regrinding...
It's all about the alloy I guess...
 

·
Registered
Joined
·
7,076 Posts
Castings can be successfully welded. But they need to be pre and post weld heat treated and the right filler metal needs to be used. Like other have said cost becomes prohibitive. If you needed a stroker bulletproof crank to replace your cast one then it would be cost effective to have a billet one machined.

If the crank is 1040 or 4340 forged steel then it can be welded fairly easily. I would post weld stress relieve it and then the journals would need to be hardened after machining.
 

·
Registered
Joined
·
6,257 Posts
Discussion Starter · #9 ·
THis is all so very interesting.
 

·
Registered
Joined
·
6,257 Posts
Discussion Starter · #11 ·
bradzuzu said:
Ya it is !! Things can be simple yet the dynamics of it can be quite a topic...
Indeed. I wish I could make my own billet crank and rods. If only I had the tools and know how.
 

·
Registered
Joined
·
13,615 Posts
I'm going to have the 3.5 rods shotpeened.. Meaning they put them into a box like a sandblaster and blast the rods with pea sized steel shot. This in turn compacts the molecular density of the rod/rods... It increases the strength by say 30 percent.. Chevy calls them pinky rods. That's what I'm running in my buggy 350 motor.. Since after market rods are unavailable for us I'm going to look into this option for my Isuzu build...
 

·
Registered
Joined
·
497 Posts
The 2.6 had a steel crank. I have been working with a grinder on a welded stroker for a project. He has no problem with working on the 2.6 crank, but said no way on the 3.2 crank. I think that if I needed a crank for a 3.2 3.5 I would buy a new one.
 

·
Registered
Joined
·
13,615 Posts
Ya no choice for them ... But that's good to hear about the 2.6's ... Have you found pistons that will clear the rotating group ??
 

·
Registered
Joined
·
497 Posts
I was trying to build compression mostly, so the increased stroke would be minor. I have given serious thought to shaving the stock pistons to set proper deck height. Basically removing the dish in the stock piston. The other route I looked into was having JE pistons build me a custom set. I just found a 96 rodeo 2.6 head and have it at the machine shop now. I need to get the new head cc'ed and see where I am at before I get to carried away with the crank.
 

·
Registered
Joined
·
1,406 Posts
My own personal rule of thumb is to never weld (or braze) a cast crank at all....you're just asking for heartbreak down the road, and only weld a steel crank if you can't get a replacement crank without selling your firstborn (unless you have plenty of kids).

I'm just uncomfortable as hell with a welded crank. I did have one welded once (it was a 421 crank from a '65 Goat) for a friend, and had to have a 354 hemi crank welded for myself, years ago, both made me nervous as a hooker in a church choir.
 

·
Registered
Joined
·
7,076 Posts
Don't fear welds. If done right a welded joint or even surface buildup is as strong or stronger than the base metal. The operator of the welder is the only one to fear LOL. Even if the crank was steel I would want it to be stress relieved in order to relieve the tension in the steel. It will also prevent the crank from distorting when the machining happens in the weld zone. Then after machining it would be a good idea to have the crank hard surfaced to produce a nice durable bearing surface.

On the topic of shot peening. It is a great idea and strengthens any machined or cast part. It also reduces the tendency for any type of crack to form. Another strength increasing process to look into is cryo treating.
 

·
Registered
Joined
·
5,214 Posts
betterthanyou said:
Don't fear welds. If done right a welded joint or even surface buildup is as strong or stronger than the base metal. The operator of the welder is the only one to fear LOL. Even if the crank was steel I would want it to be stress relieved in order to relieve the tension in the steel. It will also prevent the crank from distorting when the machining happens in the weld zone. Then after machining it would be a good idea to have the crank hard surfaced to produce a nice durable bearing surface.

On the topic of shot peening. It is a great idea and strengthens any machined or cast part. It also reduces the tendency for any type of crack to form. Another strength increasing process to look into is cryo treating.
HEY GUY,S DONT FORGET THAT ALL THE 3.2 3.5 ENG,S USE CAST IRON CRANKS NOT CAST STEEL, ALL THE RODS ARE FORGED ,STEEL SO NOT MUCH OF A PROBLEM THERE , CAST IRON DOES NOT LIKE WELDING AND DOESNT LIKE BENDING, ,, A STEEL CRANK CAN BE BENT AND STRAIGHTENED UP AS STRAIGHT AS NEW BUT CAST IRON ITS A NO NO EVEN CAST STEEL IS MORE FORGIVING, NOTHING WRONG WITH CAST IRON JUST ASK FORD , MILLIONS OF THE OLD 302 HAD CAST CRANKS AND ALL MOST ALL ENG,S TODAY HAVE CAST IRON CAM SHAFTS , EXCEPT ROLLER CAMS , CAST IRON DOES ONE THING VERY WELL, WHEN POLISHED , IT HOLDS OIL BECAUSE IT IS SO POROUS ,BUT THE OFF SETS FOR THE ISUZU ENG ON THE CRANKS JUST DOESNT LEND TO GRINDING UNDER SIZE , STOCK THEY WILL HOLD UP PRETTY WELL, .
 

·
Registered
Joined
·
6,257 Posts
Discussion Starter · #19 ·
so jerry, out of curiosity, if one were to go forced induction, whether it is supercharger or turbo, how much power can the stock 3.5L or 3.2L take before reliability becomes an issue? I know someone on here mentioned a 1000hp 3.5L in australia, but we really dont know what was done and what wasnt. Could you reliably put out 350hp on stock components or is that just asking for trouble? What about the turbo diesels that the US never got? I ask because you can import them.
 

·
Registered
Joined
·
13,615 Posts
I'm sure Jerry will concur the diesels are a different animal. Most likely with a steel crank to boot. They don't turn the rpm's gas engines do for a few reasons... Heavier components, higher compression ratio's, and the fuel trim of the injector pump or electronic injection system... Another reason they last so long,less R's....and there way over built for the rpm range they run in... If you've ever seen a ford 460 torn apart it gives you an idea of how beefy and over sized the rods and rotating group is/are compared to a diesle.... Most of them are built that way... It's to bad the 3.2's and 3.5's say in the direct injection run didn't happen to come with a steel crank.. Might have been able to transplant it into an earlier one...
I bet the engine that's producing that so called 1000hp is either none stock with the crank and rods, or it was a test to see how much one could push before exploding lol... Be awesome to find out !!!
 
1 - 20 of 29 Posts
Top