ARP rod bolt snap !

[Bender Unit]

Well all I can say is I am glad it happened as I was rebuilding the engine and not when I was driving etc.

I had just checked the clearance bewteen the rod and the crank with some pastigauge and was refitting the rod to the crank after cleaning all the plastigauge crap off.

Everything was fine and the bolts looked fine as well after the initial clearance check.

As I was doing the bolts up I was alternating between each bolt, doing a quarter turn at a time to get them to the ARP specified torque rating.

I was thinking to myself that they should be done by now when "bang" the rod bot head shot away from the bolt!

Thing is how can you get a set torque rating when the fecking bolt is stretching away.

So situation is I am now a few stages backwards, I have half a rod bolt suck in a rod which I need to try and get out and I am now dubious as to ARP's suggested torque ratings.

I was so anal with how I was doing them up. Used special moly lube as suggested and staggered the tightening to get an even tightness.

Anyone have any suggestions as to how I can go about replacing the defective rods bolts and has anyone come across this before? The bolts were supplied through Eagle and came with their H beam rods.

I was hoping to have the bottom end built this weekend!

Not my day

Cheers

James

[Bender Unit]

http://www.brown-cow.co.uk/rodbolt.htm

[Fizzy]

ive never heard of this - ever!!!! what torque did they quote?

[steve b]

i'd be more than doubtful of those torque settings looking at the pic

[Bender Unit]

They list 75lbs/ft for the rod bolts. Thing is I had already tightened them to that rating to check clearances. They clearly didnt like be done up a second time and started to deform. Looking through MR2OC in the US there does seem to be some conern regards these bolts.

I suspect I can get the broken bolt end of the rod, but I obviously now need to find some replacment bolts and knowing my luck I will have to buy new rods because of this.

Regards

James

[steve b]

ARP do a kit of rod bolts and its surprisingly cheap at £30

[JJ]

They list 75lbs/ft for the rod bolts

This not 75 Nm james ? thats about the norm... i think the stock torque is 67 nm for the bearing caps ... if this is the case .. quick calc suggest :

[Bender Unit]

Hi John,

The instructions with the rods list ft/lbs Seriously mate I was very perplexed by this and automatically assumed I had made a mistake, the torque wrench was bang on the right setting.

The instructions list

7/16 ARP 2000 7/16" bolt head - 75ft/lbs torque

Go figure?

I have read somthing posted by Ken Blake stating that these bolts supplied with these rods are no reusable. Its a case of first time round and thats your lot - nice of Eagle to tell us.

Regards

James

[JJ]

This is for the rod bolts, not the head bolts ???... sorry, I know you've been maticulous with every detail, but I have often been a spam at times seems bloody high though , you'lll be making the engine smaller with the way them arps are pulling the unit together

[Bender Unit]

Yes mate its the rod bolts, the bolts came with the rods. I thought it seemed high as well, in fact they are torqued more than the mains!

I think the engine has shrunk by a foot

Cheers

James

[Speedy]

Has it been apart before (i.e been torqued up and relaxed, then torqued up again)? - because necking is usually associated with fatigue, like you say, the bolts could just be use-once item.

[Steve Horrocks]

as you said, they are strecth bolts, now correct me if i'm wrong, but stretch bolts do exectly what they say on the tin and can therefore only be used once.

[paul port]

If they were stretch bolts, would Eagle / ARP not have specified the torqueing procedure as XXNm + 1/4 turn or similar (think Toyota head bolts)

Saying that... the ARP website does list their rod bolts as stretching a little, also 30-50 Ft/Lbs depending on model:

http://www.arp-bolts.com/pages/tech/images/rod_bolt.pdf

So how do you go about plastigauging if you can only torque the bolts the once?

[lower]

presumably you have to sacrifice a set of rob bolts to check the clearances are correct and then put another set in when you reassemble the engine for real.

[Fizzy]

Having seen the diamiter of the bolts I think it HIGHLY doubghtful that 75 ils is correct - Ive torqued down head bolts to less than 50 on full race engines ( tighter is not always better with soft heads!!!) so 75 for an end bolt seems massive - would have expected to see 35 - 40 max. Daft question but have you used your torque bar to hammer any nails in recently???

[SimonPearse]

have you contacted ARP... I guess that they are protective of their reputation so they may want to be helpfull...
If you are certain that 75ft lb is the specified torque have you checked your torque wrench calibration against another wrench (find someone with a wrench of a different brand, connect them together and apply torque against each other. Its no certainty, but if they read approx the same then the are probrably reasonably accurate.
If you have a spring-loaded type wrench they are supposed to be stored with the spring fully unwound, otherwise they drift out of callibration.

[Bender Unit]

Turns out they were over torqued . Still never mind, Eagle were very helpful and have buzzed me out some new ARP bolts to replace the stretched ones, should get them by thursday. Happy days!

The ARP bolts are clearly very tough to have taken considerably more torque than what they are rated too!

Cheers

James

[paul port]

So what WERE they supposed to be torqued to?
And are they actually stretch bolts (thinking of plastigauging)

paul