Quaility control?

I was going to put Honda Connecting Rods in an MG as a cheap upgrade.  Honda has a reputation for reliability and the MG rods were probably designed in the 1930’s  

On paper things would fit or could be made to work until I started to check them out last night. 

Total weight of the rods varied by over 56 grams from the lightest  to heaviest. With big ends varied by as much as 39 grams.  

How the heck do you balance something like that?  You grind that much weight and you are bound to weaken the rod.  

I know they came from a virgin engine because I pulled them myself. 

Other engines I’ve worked on can have as much or more variation but they are batch mixed so they don’t vary by more than a few grams  total weight and less than 2 grams on the big end. 

The trouble comes when you mix rods from different engines. 

Batches vary. I have run in to this with Toyota rods when I was building 4age motors for various race cars. I spoke with Toyota and they attributed it to tooling ware. Where it got to be a big problem was when you got parts like pistons and rods that were on either end of the tooling life cycle. Having the small end of a rod be at the maximum allowable side of acceptable and a piston wrist pin hole be at the minimum and the wrist pins being sized to the rod will many times lead to galling of the alu of the piston wrist pin hole.  To get a blueprinted motor using factory parts took a lot of mixing and matching as well as having factory new parts being sent to the machine shop to be properly sized.  I also returned many sets of pistons and rods to the dealer due to them not being to a spec that would work with the other parts I was using.  

Regarding 56 grams coming off the big end. Since the lightest one already has it missing I would not be extremely worried about it. I would not like it. I would be looking to get another set and see if you can mix and match and get a better base line set. 

dean1484 said:

Batches varry. I have run in to this with Toyota rods when I was building 4age motors for various race cars. I spoke with Toyota and they attributed it to tooling ware. Where it got to be a big problem was when you got parts like pistons and rods that were on either end of the tooling life cycle. Having the small end of a rod be at the maximum allowable side of acceptable and a piston wrist pin hole be at the minimum and the wrist pins being sized to the rod will many times lead to galling of the alu of the piston wrist pin hole.  To get a blueprinted motor using factory parts took a lot of mixing and matching as well as having factory new parts being sent to the machine shop to be properly sized.  I also returned many sets of pistons and rods to the dealer due to them not being to a spec that would work with the other parts I was using.  

I’m really surprised at the lack of quality of motor parts in some of the most reliable  imported cars.  But over 50 grams? !  

When I built Jaguar race engines if a rod was outside 2 grams  I got all upset. And used it as justification to buy all the engine blueprinting equipment. 

On  the other hand maybe that’s why my engines lasted for the decades they did.  

I watched a UTube video on building the V12 and saw how they’d batch rods ( and other parts) to specific weights. I just assumed it was because their volume was so low ( some years under 1000 were made)  they had to do that.  

dean1484 said:

Regarding 56 grams coming off the big end. Since the lightest one already has it missing I would not be extremely worried about it. I would not like it. I would be looking to get another set and see if you can mix and match and get a better base line set. 

I agree that much difference is too scary, but apparently Honda was OK with it.  The engine came out of a rust bucket I bought for scrap value and was a virgin, never been opened up.  

I think I’m going to look at motorcycle engines as a source for rods. Some of those have extremely high red lines. 

I've heard gold wing rods are swappable into some small car engines. Maybe something to look into.

In reply to Robbie :

Thanks, good idea!  There is a motorcycle salvage  near here so I’ll look into that.  Plus craigslist. 

Or get a couple of sets or rods, do what you just did to weigh them, and get a set that's much closer, then grind the balance pad (if there is one) until they are equal.

I’m not too surprised there’s that big a difference in weights but I’m kinda surprised they’d be that different in the same engine. For some reason I assumed they’d try and put 4 similar ones together.

What model Honda motor ?

What does the factory repair book say as far as rod weights ?

We were thinking of using Honda rods on a project but if 50 grams is normal then maybe we need to rethink that idea

How close was the center to center distance on the 4 rods ?

This really makes you rethink how detailed we thought Japanese motors are built !

Appleseed said:

Or get a couple of sets or rods, do what you just did to weigh them, and get a set that's much closer, then grind the balance pad (if there is one) until they are equal.

I’m going to build a MG. T series engine with my spare block. They want nearly $3000 for a billet steel crank $1000 for rods and almost $4500 for a Eaton 45 supercharger. 

My goal is to do all that for under $2500 

I’ve got a block of SAE 4340 steel that is about 50 hours from looking like a crankshaft and since it’s hidden away I may as well use cheap readily available connecting rods. All I need to match is the main bearing size. Whatever is required for the rods is simple. I checked and my lathe has enough swing to give me at least the stock stroke. I’ll rough everything out and let the local crank grinder bring it to final finish  

 I’ll bore the block out to whatever size I need for off the shelf pistons.  Same with the oil pump.  There are aftermarket roller camshaft available.  

A full charge racing MGT series engine can easily cost over $15,000 in parts and still make less than 100 horsepower. All the time risking completely coming apart  and ventilating the block. 

Annual rebuilds  sort of start at $3500 and because of the antique design of the camshaft are almost mandatory.  A roller cam eliminates the annual rebuild requirement  

Considering Honda still believes that a quart of oil per 1000 miles is acceptable oil consumption oil in 2018 I do t think their overall QC is that great personally

I’m inordinately pleased that a thread about quality control has a typo in its two-word title. 

Well, to play devil's advocate here...

If the engine is designed to accommodate those deviations in rod weight and perform satisfactorily, it is possible that the rods are within tolerance and there is no quality control issue.  

Production tolerances should be based on both the ability to produce cost effective components within spec and the larger units ability to perform for the required life cycle using components within the specified tolerances. The greater the tolerances that can be accommodated in the design, the more allowable variation in part production.  So, using more material to reduce stresses in the crank, bearings, and rods may be cheaper than machining the rods to tighter tolerances.

secretariata said:

Well, to play devil's advocate here...

If the engine is designed to accommodate those deviations in rod weight and perform satisfactorily, it is possible that the rods are within tolerance and there is no quality control issue.  

Production tolerances should be based on both the ability to produce cost effective components within spec and the larger units ability to perform for the required life cycle using components within the specified tolerances. The greater the tolerances that can be accommodated in the design, the more allowable variation in part production.  So, using more material to reduce stresses in the crank, bearings, and rods may be cheaper than machining the rods to tighter tolerances.

I’m sure you’re right. Few people obsess about  engine quality. Seldom  if ever running the engine to red line. Price is everything. 

Duke said:

I’m inordinately pleased that a thread about quality control has a typo in its two-word title. 

I didn't even notice that. Now I can't stop smiling. 

Whatchou talkin’ about??