Why Engine Disassembly Inspection is Important.

fordboy628

Moderator
Staff member
Warning!! Reading this thread might make you "smarter". (or it might not . . . . .)

I wish I had $10 for every racer who verbalized the statement: "I can build an engine as good as anybody!" I could have retired long ago . . . . . . .

Well for starters, the above statement is grammatically incorrect. (Thank you Sister Justilla for all those grammar explanations . . . .) And, as it turns out, these are the same folks who are having engine problems at the track, loading up their trailers early and mentioning to anyone who would listen: "Gonna get this puppy home, pull the engine, and get it ripped apart ASAP, so's I can make the next race."

Whoa, there Seabiscuit! You just might want to spend a bit more time on the "post mortem" of your little jewel. I am the first person to endorse speedy disassembly of race engines. In "production" environments where I have labored, speed is essential. And for engines which do not exhibit any problems, speedy disassembly is warranted. But for engines which have issues, a careful and "deliberate" post mortem inspection can identify "issues" which need to be corrected.

Some examples:

A/
Checking the break away torque on fasteners after a failure. A bending beam torque wrench is useful for this. Record the values and compare to installation values. You DO keep records of these values, don't you? How do you check if you don't?

2/ Careful measurement of critical component dimensions. This requires precision measuring tools. Micrometers, dial bore gauges and the like. A pronouncement such as: "If you need to check dimensions, you need a new machine shop." are optimistically simplistic. The person who assembles the engine is the one who bears the responsibility for final dimensional checking. Any human being can "make a mistake". Trust, but verify . . . .

d/
Careful visual inspection is also required, prior to other inspection processes such as magnetic particle or dye penetrant. Looking for signs of the "unusual" is a required portion of the disassembly, especially after any failure.

Some photos of what I'm talking about:


59

Some "fretting" on a 4 bolt main cap, due to insufficient fastener pre-load. High quality fasteners were used, but the "assembler" substituted AN washers for the hardened washers that came with the fasteners set. The AN washers could not withstand the tension load imposed by the fasteners, and compressed as a result. This "washer compression/distortion" reduced the fastener assembly pre-load, reducing the "clamp load" on the parts. This in turn allowed "movement" between the parts, resulting in the "fretting" shown in the photo.

When I pointed this out to the "assembler", and asked why the issue had not been corrected, the reply was: "Those parts always look like that."

Needless to say, parts should not exhibit that kind of wear.


NOTE:
I tried posting a photo of the "distorted washers", but the "file was too large". If I can edit the photo to a smaller, acceptable size, I'll edit it in to this post at later time.

Cheers
 
Last edited:

fordboy628

Moderator
Staff member
Some more photos for the preceding post:

60
Another view of the "fretted" main cap.


61
Distorted washers too "soft" for the application.


62
Comparison of hardened 8740 chrome moly material washers Vs. "steel" washers which failed.


This is another example of how "little", seemingly insignificant, details matter.

A/ On "professional" race teams, engine assemblers are knowledgeable, very skilled, and detail oriented individuals.

2/ If you are the "head engine assembler" for your "race team", you must also have the same skill set to be successful.

d/ OR, you must recognize your own "limitations", and engage the services of those who can provide you with the quality needed for success.


"It's complicated." A phrase everyone is tired of hearing, but with examples like these, one I will continue to repeat. The "trick" is to be better or smarter, NOT to work harder for a "poorer" result . . . . Think about it.

Cheers
 

tabsracer

Crazy about Datsuns
Awesome stuff! The phrase, "The Devil is in the details" comes to mind if that is the correct phrase? lol
Those photos show it all. The washers look like oil pan crush washers.lol
Cheers
 

fordboy628

Moderator
Staff member
Awesome stuff! The phrase, "The Devil is in the details" comes to mind if that is the correct phrase? lol
Those photos show it all. The washers look like oil pan crush washers.lol
Cheers
Yes, that phrase works. However I prefer: "God is in the details." Meis van der Rohe

Well, actually, they WERE crush washers! They were not supposed to be though.


Engine "engineering" demands attention to "details", if there is to be a reasonable chance of success. It is a case of making your own luck.

Cheers
 
Hey guys, long time away, I finally figure out how to get back on here :) This is on street engines, but Moss Motors ask me to write a article about engine assembly in their Moss Motoring magazine, I told them I would only do so under one circumstance, I first wrote one about disassembly. Both the disassembly and assembly articles I wrote theme's would be "tips beyond the shop manual". In the disassembly article I wrote, I encouraged people to do more of forensic examination of things as they disassembled, to get as many answers at that time as possible on the condition of the engine.

Mark, I find too many people today let their minds drift as they are working, I can say when I am working on an engine, porting a cylinder head, I am totally focused on that task at hand, it by far is more interesting than anything in my head :) , and if it's not, then I need to find another line of work.
 

tabsracer

Crazy about Datsuns
Hey guys, long time away, I finally figure out how to get back on here :) This is on street engines, but Moss Motors ask me to write a article about engine assembly in their Moss Motoring magazine, I told them I would only do so under one circumstance, I first wrote one about disassembly. Both the disassembly and assembly articles I wrote theme's would be "tips beyond the shop manual". In the disassembly article I wrote, I encouraged people to do more of forensic examination of things as they disassembled, to get as many answers at that time as possible on the condition of the engine.

Mark, I find too many people today let their minds drift as they are working, I can say when I am working on an engine, porting a cylinder head, I am totally focused on that task at hand, it by far is more interesting than anything in my head :) , and if it's not, then I need to find another line of work.
Welcome Back!
 

fordboy628

Moderator
Staff member
This is a duplicate posting from my Racing Engines thread. I put it on this thread as well because search engines do not always offer connections to every thread.


Once again, down the same rabbit hole . . . . . . part 2 . . . . .

Well, I confess: I'm getting tired of a being a "racing engine coroner". . . "It's like deja vu, all over again." Yogi Berra

No photos of these bits either, a courtesy to the owner. However I know the owner is a "reader", and perhaps may post photos of the "carnage".


This past Monday, a third party brought by the shards of one of the latest BMC 'A' series engine failures. It wasn't a typical failure, as it was a breakage involving "premium quality parts". The failure was a broken, aftermarket "Carrillo style", H beam connecting rod. I think it was in fact, an actual Carrillo (or CP Products now) produced part. Atypically, the rod broke just above what rod manufacturers call the "shoulder" of the rod. This area is just above the "big end", where the beam of the rod narrows heading up to the pin end. This narrowing is required for the rod's big end to clear the bottom of the cylinder walls as the crankshaft rotates. Needless to say, when the rod separated into 2 pieces at high rpm, BAD THINGS happened as a result! The remains were in at least 4 large pieces, and many smaller shards.

The question became: "It's a Carrillo rod, how could this happen? ? ? ?"

Well, let's do a bit of thinking about this question, and this failure . . . . . .

It seems that there is a presumption that, somehow, premium quality aftermarket parts are "indestructible". This is, of course, untrue. But after racers pay out their "big bucks", however, most racers would like to think: That item is "forever".

You are not buying a "diamond"! ! ! (And despite what De Beers claims, even diamonds are not forever . . . .)


OK, OK, I'll get back to reality then . . . . .

A/ H beam connecting rods are usually used because they can be made LIGHTER than I beam connecting rods.
It's a fact that the rod set in question was made for maximum lightness, ie: minimum weight. Premium quality material and premium quality 5/16" rod bolts were used. The ONLY reason to do that is a quest for minimum weight. There can be "advantages" to minimum weight. There are also "disadvantages" . . . .

2/ Note that lighter components are usually LESS durable than heavier parts.
These Carrillo rods are sub 490 gram total weight each. Compare that to the ultra-heavy stock BMC rods weighing 680 grams each, using 3/8" rod bolts. I'm not going to cover this topic again. Go back and re-read reply #21 to this thread. It concerns materials science and reliability.

d/ And there are "other" factors.
I have seen this type of failure previously, on several occasions, for several reasons:
1/ The previously mentioned durability cycle/lifespan reasons.
2/ Unknown inclusions (defects) in the beam of the con rod. Quality manufacturers x-ray every rough blank con rod, and reject those with this type of defect. Lesser manufacturers may not do the same. And there can be "mistakes", despite the best intentions.
3/ Mechanical interference: H beam rods are wider than their I beam counterparts. I have seen engines where inadequate clearance existed between the "shoulder" of an H beam connecting rod and the bottom of the cylinder. Even slight contact between the shoulder of an H beam con rod and a cylinder with inadequate clearance, results in disaster.

So what's the answer?

Well, if you are racing for money or prestige, the lightest weight (mass) components can give you an advantage. This is merely the math, and professional racers accept the risk and the cost of periodically replacing components. This is why ebay has countless "slightly used, but cast off" components for sale. Professional teams use these components for a set number of miles or hours, then discard them. The idea is to prevent a component failure while perhaps leading a race. Statistical analysis proves this to be a sound methodology for success, in spite of increased cost.

But what if I'm racing for "fun"?

If that is the case, then your decision criteria are probably different. The final decision about component weight and the resulting reliability gets to be made by those whose "checkbook does the talking". The decision is: "unlimited" component life Vs. the perceived advantage of light components.

Caveat emptor!

:cheers:
:dhorse:
 
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