34 replies to this topic

[JonnyAlpha]

Hi;

 

I am rebuilding / reconditioning a 1275 Metro.

 

The block has been bored and once I receive my dummy fit Gudgeon Pins from AC Dodd, I was going to do the trial build using the standard bolts. And then get a set of ARP Conrod bolts for the actual build, figuring that I wouldn't want to torque them twice.

Although looking at my Engine Build Info, kindly sent to me by Cooperman, the advice is to torque the rod bolts to 25lb ft for the trial build.

 

I have just been advised however on a FaceBook group that if using ARP studs the Big Ends on the Conrods may need to be re-sized!! That's the first time I have seen this mentioned and has received several replies saying the same - new bolt = close and hone (re-shape) now looking for advice on here.

 

 

[ACDodd]

Measure them with the bolts torqued. If their is a mismatch, or they are oval, too big or too small, or tapered have them resized.

What people say and what is fact (found by measurement) are usually two different things.

Ac

Edited by ACDodd, 14 September 2019 - 09:57 AM.

[JonnyAlpha]

Measure them with the bolts torqued. If their is a mismatch, or they are oval, too big or too small, or tapered have them resized.

Ac

 

I was going to get the Conrods checked and balanced by the machine shop but should this be done with the new (ARP) bolts or with the old?

If it's done with the new ARP bolts can they be re-used?

[Cooperman]

You can re-use con-rod bolts so long as they have not been over-torqued to beyond their 'elastic limit'.

When you have previously bought new bolts and done the builds yourself, you will know whether over-torquing has ever taken place. 

The reason for fitting new bolts is when rebuilding a previously unknown engine you don't know what previous owners have done.

Of course, with a competition or very high-revving engine some extra strength is sensible which is why the ARP bolts/nuts are so popular.

Personally I re-use the ARP bolts in my 'S' when 'refreshing' the engine.

When doing the trial build, I normally torque the big-end bolts to 25 lb.ft as that allows me to check for free rotation and do the necessary measurements (e.g crank end float, piston top to deck, etc).

[JonnyAlpha]

So, assemble the conrods with the new bolts on the bench, torque them up.

Then check the internal diameter of the big ends. If oval get them resized.

The same post on Facebook then suggested to check the bearings the same way?

 

When checking the conrod big ends on the bench, do you torque them to specified torque (based on the bolts you are using, or do you torque them to 25%. 

[ACDodd]

Torque to specified setting

Resize (if needed) with the new bolts fitted.

Ac

[mini13]

I agree with both of the above, when trial building I nip stuff up spanner tight to check for binding, check deck height, things like that, also I normally have a "sacrificial" set of new bearings for the sort if going and swap in a new new set for final assy.

Another thing I generally do us run floating gudgeon pins, either in pistons with clips, or pins with ptfe pads, that means it's much much easier to swap stuff round or replace pistons, but that's just me, obviously there are some drawbacks.

[mini13]

Also, sometimes you just have to draw the line in measuring as it gets out of hand, generally for standardise stuff I'll assume the block mains and rod bigness are OK, if it's a pokey build then I'll measure. Same with rod length, and crank bend,

[JonnyAlpha]

Torque to specified setting

Resize (if needed) with the new bolts fitted.

Ac

And then again on the bench with the bearings fitted?
Doing them up to 55lb (which I think is the ARP setting) gonna have to hold them tight in the bench

[ACDodd]

No, I use arp lube the torque setting us much lower, like 34lbft. I do not fit the bearings. Tunnel diameter is 1.8955 to 1.896". The images show a 998 rod being done on my mill.



Ac

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Edited by ACDodd, 15 September 2019 - 06:44 AM.

[JonnyAlpha]

ARP Bolts arrived today, supplied by MED Engineering. No installation instructions so I guess I'll have to find it on the ARP web site?

These are the A+ Conrod Bolts.

 

They come with some ARP Torque Lube, I guess there is enough for a trial and real build of all 8 bolts?

 

[Spider]

A bit broader than the original thread topic but it's really not possible to look in isolation (in the total context of the thread) at just the Rod Cap Fasteners.

 

Accepted Engine Reconditioning Practice is to Recondition Con Rods when overhauling an Engine. This includes Crack Testing, Little and Big End checks, Signs of heating (particularly in the Little End), Rod Cap Location, Checks and Corrections for Rod Bending and Twist, Thrust Clearances and Wear, Spot Facings, Replacement of the Cap Fasteners and re-sizing of the Big End.

 

They are so often over looked and a good percentage of Engine problems, can be tracked down to the Rods. I'd never assemble an Engine without doing the above to the Rods.

 

Replacing the Cap Fasteners means Resizing the Big End. Even if Stock Fasteners are used. This is accepted Engine Reconditioning Practice and it's also a procedure of ARP's;-

 

 

Also;-

 

 

For completeness;-

 

 

Always torque the Cap Fasteners to the Recommended Torque, even for Sizing and Rotational Checks. Any change from that will change the shape and size of the Big End. 99 999 times out of 100 000 you'll be able to re-use the same fasteners if new and of decent quality during the reconditioning of the Rods, to final fitting. This is largely because the Fasteners, while having been Torqued up haven't be subject to the stresses of having been run and loaded up.

 

You'll find a chart in the ARP Packet under the Grease, however I cannot recommend enough that you down load the ARP Catalogue and read all the tech info in it. Unfortunately, it's scattered throughout the book.

 

 

The images show a 998 rod being done on my mill.

 

Ac

 

'Interesting' finish from the fly cutter in your Mill

[ACDodd]

Same as that produced on the lathe.

Ac

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[JonnyAlpha]

So after I received the ARP bolts / nuts I received my Moore and Wright Micrometer set and some Draper Expert Telescopic Gauges.

I now need to check the ConRods so I need to know the Conrod Specifications and tolerances.

This is a 1275 A+ pulled from a 1988 Mk2 Metro.

 

What are the Conrod specs, e.g. length (where is this measured?), small end (internal) big end (internal).

 

I found this really informative thread here with this info but just wanted to double check.

 

In the above post it also talks about Piston to Rod fitting process and states that the pins should be cold pressed on and definitely not heated. When discussing how the pins are fitted, machine shops that I have talked to here have said that they heat up the small end?

What is the correct process?

 

Thanks 

[ACDodd]

Big end tunnel bore diameter is 1.8955 to 1.896"

Small end, simply measure the piston gudgeon pin diameters. The small end of the Conrod must be a minimum of 0.0008" smaller.

As regards fitting, I use the heating method. However if you don't know what you are doing overheating will soften the steel.

Ac