Rods Don't Fit Journals

[Dennis Vogel]

This is not a situation that you can resolve yourself... I would say take it to the machine shop that did your work...

Hi Al. You're correct I can't solve it at this point. Just searching for root cause and trying to educate myself. I took the crank, rods, and bearing back the machinist this week. I heard back today that "There is definitely a problem with the crank". I'll get the details on what that means next week.

I'll probably just buy a new AA 356 / 912 crankshaft at this point.

[Wes Bender]

I hope that doesn't mean he's going to modify the crank so that the thicker rods will fit. What did he say about the difference in the rods?

[Tim Berardelli]

Dennis,

Total rod weight is meaningless, the total weights for the rod can be within the last published Factory spec,6 grams difference max yet when all the "big ends" and "pin" ends are weighed separately the numbers can easily exceed that Factory spec. As a good litmus Test ask your Machine shop to define "end for end balancing" for connecting rods.

[Dennis Vogel]

...when all the "big ends" and "pin" ends are weighed separately the numbers can easily exceed that Factory spec. As a good litmus Test ask your Machine shop to define "end for end balancing" for connecting rods.

Our machinist did provide the big end weights as well. I just wasn't able to verify them myself. The max variation between the big end weights was 4 grams (i.e. difference between lightest and heaviest of the four rods).

[Dick Weiss]

Dennis,

Measuring the thickness of rod bearing/inserts require a ball-end Mic; Using a vernier caliper won't be accurate enough for exactness. Also, rod inserts are marked on the backside w/std, -0,25, -0,50,
and even -0,75. There are times when you can't trust the #s on the box--ditto w/main bearings!

Dick

[Dick Weiss]

Again, Dennis;

The machinist should NOT modify the crank's journal widths to suit the 2-rods. Cheaper to buy
replacement rods--I have a new set, or @ less cost refinished & balanced set of -00 or -01.

Dick (Or refinish yours to match & balance)

[Martin Benade]

Sounds like the crank grew. (Welded)

[Vic Skirmants]

How about just hitting the sides of the rods with a belt sander? When we were still using stock rods in our race engines, that's what we did to increase the side clearance for better oil flow. The side clearance does not determine the oil pressure, the crank to bearing clearance does that.
We've just spent three pages of posts to try and fix a simple problem.

[Thomas Sottile]

Vic that's too easy.

[Dennis Vogel]

An improperly welded crank could “grow” narrower.

Today I received a new AA crank from my vendor, to rectify the situation. It has been a painful waste of time for both of us. I give him credit for standing behind his parts and work. I know he ate some profit due to the lack of integrity exhibited by the person he originally sourced the crank from.

His analysis of the problem crank is that it was welded and whomever did the machine work did not leave proper clearance between the journals. Evidence he pointed to includes the rough edge I've circled in the attached. He suspects that if it was in fact out of a running engine, those rods were probably sanded down to fit between the journals (per Vic's comment).

Now we try again with a new crank! With all spinning components balanced, hopefully it will be smooth sailing from here on out...

ReplacedCrankWelded.jpg (669.83 KiB) Viewed 1112 times

[Ernesto Cabrera]

You have sufficient side clearance, so chances are you may have gotten some mismatched bearing shells. Compare the bearing thickness to the ones that fit.

[Martin Benade]

I have taken a cross country trip years ago running a welded crank that did fine. In spite of that, it’s less than ideal so they did you a favour with the poor work. Now you have something more trustworthy.

[Al Zim]

This was a fraudulent transaction from the beginning! the person you purchased the crank from purchased the crank as a new crank from a Registry member. The seller knew the crank was defective and sold it swindling the purchaser. The purchaser has tried to get his money back without results. Further inquiry has revealed that the crank was ,originally sold by AAA. al zim

[Harlan Halsey]

You could, of course, buy a SCAT crank from Shasta Design, measure it and be done, rather than get another cheap Chinese copy.

Years ago we used to rebuild our 356 engines without benefit of measuring equipment or even many tools. We could do that because we were working on engines which had never been apart, and because we were using all factory parts. Today, never been apart engines are rare, and assembling an engine from mismatched old junk, requires a lot of measurement and judgment. Even the most expensive after market parts have to be measured and usually, corrected and sometimes returned for to the maker correction.
The colorful gone but not forgotten Harry Pellow had a name for those who do but don't know how. It seems to me that since Harry's time, the internet has facilitated the breeding of Turkeys.

[Steve Hatfield]

Their now much worse then Turkeys by their veracious appetites for the all mighty dollar. Maybe a better term, their now Gobblers.