ARP rod bolt conversion. - Alfa Romeo Forum
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(Post Link) post #1 of 4 Old 01-09-13 Thread Starter
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ARP rod bolt conversion.

Here is how I converted a set of 33 rods to accept ARP 3/8 UNF bolts.
Im not going into details of basic workshop practice here, if you don't have any experience doing this kind of thing I wouldn't recommend trying this.

2013-08-05 17.26.41 (Custom).jpg
Tools needed:
10mm Chucking Reamer
"Q" Chucking Reamer
Tap holder
3/8 UNF tap set (Only the starting and bottoming tap are needed)
Tap with a ground point for locating taps. (or anything with a ground point)
Set of ARP 2000 1.5" 3/8 UNF Rod bolts, 1.75" might be better but Ill get into that later.
Cut down original rod bolt for locating rod. Uncut bolt for reference.
Milling machine, if you have a quality drill press and vice you could use that if you were careful.

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Screw in the cut down bolt

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Tighten the bolt into the chuck, making sure its on center.

2013-08-05 17.30.53 (Custom).jpg
Wind the rod into the vice making sure it isn't being pushed forward or backwards, clamp down on the rod, I used a dial gauge to check the rod isn't being pushed in either direction when tightening the vice.

2013-08-03 18.28.50 (Custom).jpg
Tighten the beds on the mill, undo the the chuck and remove the cut down original bolt.
Tighten the "Q" reamer in the chuck and ream the original thread out. A small amount of thread will be left.

526407_10151809021058352_8301722_n (Custom).jpg
Remove the reamer and tighten the pointed tap into the chuck. Use the point to keep the tap vertical as you cut the tread. You "chase" the tap as the thread is cut, repeat for the bottoming tap. I found there was no need to use the intermediate tap.

More to follow...
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(Post Link) post #2 of 4 Old 01-09-13 Thread Starter
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972306_10151809020663352_1569148826_n (Custom).jpg
Ream out the holes in the rod cap to 10mm, I used a similar process to align the rod cap for reaming as I did with the rod using a cut down 9.5mm drill bit in place of the rod bolt.

This photo is just a mock up, I forgot to take one during.

The original hole in the cap is 9.5mm and the land on the original bolt is 9mm leaving 0.5mm clearance

The Land on the ARP bolt is 3/8 (9.525mm) that is my reason for reaming out the caps to 10mm, to allow the same clearance as the original caps.

1077475_10151809021233352_188272461_o (Custom).jpg
Close up of thread

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1146226_10151809021328352_1576677758_o (Custom).jpg
Finished rod.

As it stands the 1.5" ARP bolt has 7 1/4 turns of thread when tightened by hand, the original bolt is 8 1/2 turns.

I think the 1.5" bolt will in all likelihood have enough thread, but I may use the 1.75" bolt.
The 1.5" leaves 7.5mm of thread left in the rod and the 1.75" bolt is 6mm longer than 1.5".

Last edited by 81sprint; 01-09-13 at 05:48.
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superb work, really neat.
good to know how things should be done

can't imagine i'd get anything like the same results with my 10 homebase drill and wobbly bench vice

love these sorts of posts, cheers
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Me too.....!

Absolutely fascinating. Must have spent a good 20 mins just looking at all the photos and studying the text.

(clearly as my engine is starting to come together I have a heightened interest)

Will see what the engine builder has to say when the new (to me) rods land and see what advice he gives.

Will take it from there.
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arp , bolt , conversion , rod

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