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Manley I beam rod specs. and tolerance

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I have manley turbo tuff i beam connecting rods, had an engine failure 4g63T. The rods seem to be torch burnt, rod big turned blue.

The con rod bearings suffered the fury, now i want to check if those rods are still with in specs or i should throw them straight away ?

I did some measurement on the big end upper half width and big end lower half [ rod cap ] width . From manley's website Big end width for turbo tuff i beam rods 7 bolt crank is 26.365 mm.

1st cylinder upper= 26.30 lower=26.29 , 2nd cylinder upper=26.30 lower= 26.31, 3rd cylinder upper=26.26 lower=26.27, 4th cylinder upper=26.31 lower=26.34.

ARP 2000 rod bolts that came out from the rods measure

50.57 mm 50.67, 50.59 50.76 50.70 50.67 50.60 50.58.

I want to know , how much of a tolerance is acceptable if i want to re use these rod bolts and these connecting rods ?

There is no precision machine shop in the area i live in.

The blue colour is from the rods being overheated (friction from contact with crank-journal). This overheating can change the metallurgical properties of the steel (in a bad way... of course). Contact the manufacturer.

The big end width is probably one of the less critical measurements of a conrod. This effects the side clearance of the rods when installed on the crankshaft journal. On a 4G63 I normally aim for around 0.010" clearance here (0.254 mm). More critical though is the big end tunnel size and this can be effected by a run bearing.

Marek is also correct - If the rod has been discoloured it may effect the heat treatment of the material. I've had similar problems in the past with an Australian brand of rods. I sent them back and had them resized and tested. Often you need to weigh this up against the cost of the rods in the first place.

If they discolored they are usually no good. But you must determine what was the cause of the oil starvation. I would install at least new bolts, if you do reuse em. If its a single rod then you can just order one from manley directly. I've done so in the past. They are really good rods, especially Turbo Tuff ones. Either the rod bolts weren't preloaded correctly or more likely you have oiling issues.

The con rods of the 1st and 2nd cylinder turned blue, 3rd cylinder rod suffered less and 4th had nothing . The bearings of the 1st and 2nd big end journal looked as if some thing pressed them from the top with alot of force. Oil pump failure, generally results in all the bearings running dry or their notch got broken. Here none of the bearing notches got broken, which points out towards knock. I remember Andre explaining in one of the webinars that knock and pre-ignition produce cylinder pressures much higher than normal. Today i will take a detailed look at the oil pump and stainer . Up till now i didnt find any debree stuck inside the oil stainer and oil adapter housing.

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Oil pump failure is not the same kind of failure as oil starvation is. Although both are related and show similar traces of "unhappiness", broken bearing notches are a sign of a violent event juust before friction welding occurs. Your engine "could" have failed due to starvation, although from what I see and what you are describing (flattened bearings), I am leaning towards detonation, probably light but, prolonged detonation. NO way I would ever re-use such a discolored rod! The crankshaft bearing journal looks as if it could be reworked.

Can you clean, non abrasively, the piston heads? It would be interesting to see if there is any kind of lightly sandblasted appearance on the piston crown, especially near the edges of the piston.

Flattened bearings can also be caused by the inertial load of rod and piston mass... after the bearing has been softened up from the friction heating.


A lot of interesting things happen when there is lack of lubrication, sure. Knock can have an adverse effect on the oil film on the crankshaft journal!

What friction are you referring to? The sides of the connecting rod touching the crankshaft ? That would be an utterly bad engine building job, as the rod will never touch the crank if it is assembled properly, and it is almost impossible to ill assemble an engine like that (to my knowledge).


Oil starvation only in 2 rod journals ? 3rd suffered less and 4th not even a scratch ? in my opinion ,things dont add up.

I will clean the pistons today and take a look at main journal and bearings to see the complete story.

It was surprising to see the crank shaft. I measured the outer diameters of main journals and rods journals

Mains = 56.96 mm , 56.91, 56.91, 56.92, 56.91

Con rod journals = 45 mm all four.

The rod journals just got bearing colour on them no wear, oil pump was ok, no metallic debree found inside it. Out diameter of all the journals is up to the specs. Very odd.

I checked the bearing oil clearance of this crankshaft with plastigauge . OEM rod bearings + rods + 15ft lbs + 90 degree. Came with in specs 0.38 mm.

When ever we use ACL race bearings and torque them with OEM rods or any after market rod, the rods move freely but with standard bearings they seem to be tight as they should. Why is this so ?

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what clearance on your mains?

Just checked the outer dia of mains, didnt check clearance .

Rule #1. Do NOT use "plastiguage" on a high performance engine. Either get proper measuring instruments or get a shop to measure it for you.

And what do you mean by "tight"?.

I wrote on the first post, we dont have any machine shops here, plasti gauge is the best i can do. 'Tight' means movable but not freely movable like ACL. If you have worked with OEM rod bearings you will definitely know the difference between them and acl. They are a bit loose on the rod journal.

Dude!... you actually have an interference fit between rod bearings and crank!?... this means you have NO clearance!. Rather... you have *negative* clearance. The rods should ALWAYS rotate freely on the crank. When you slowly spin the crank with rods connected... the rods should always be pointing straight down... even with too little clearance they will still move freely with no binding. I suggest you invest in an external micrometer and appropriately sized telescopic gauge (and learn how to use them properly)... this way you will know exactly what bearings to get and you'll also be able to measure the bearing thickness.

No machine shop in Monaco huh?! Is that the place where the filthy rich throw away the cars when the first oil change is due?

Let's open a shop there

@Dynodom, LOL!

You need to invest in a set of micrometers!!!!! Mitutoyo is my preference with at least 0.0001" resolution but they are pricey. You also need a dial bore gage with .0001" dial bore indicator. Most are 2"-6" so if you want to measure rod bearings installed in the rod you might need ones that measure from 1.4"-2.5" dial bore set. Telescopic gauges are ok, but they require a lot of time to learn how to get the "feel" for it. Dial bore gauges will give you an instant reading. It is a pricey investment especially if you buy Mitutoyo but its cheaper than rebuilding an engine or blowing one up. Also invest in a Timing wheel so you can check piston to valve clearance while you're at it. If you cant afford any of the above you should find a machine shop. Plastigauge is good to double check your work but I wouldn't use it as you're only way to measure clearances. also check this out. ACL race bearings has done the work for you.

Mitutoyo are the best, no doubt.


Thanks for the detailed reply. I would definitely buy one and use it.