924Board.org

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

Has the known supply of ARP rod bolts been depleted? I think I read that someone bought Dan's last set...
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81 924 N/A

2004 Ranger "Edge"

2005 Mazda 6

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Fifty50Plus · Posted: Wed Sep 28, 2011 2:26 am Post subject:

Time for another group buy? I'd be in for a set.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

MikeJinCO · Posted: Thu Sep 29, 2011 5:01 am Post subject:

I'm going to need a set by next summer for a new HC motor. So count me in also.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

Anyone experiment with different brands? With the amount of engines out there that have been produced there has to be something that is very close to the same size bolt. Sometimes you have to think outside the box

If I had some extra rods or the messurments I would do some research of my own
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81 924 N/A

2004 Ranger "Edge"

2005 Mazda 6

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

When we first had these made, I sent samples to ARP and they checked their entire catalog for a "close" replacement, but turned up nothing. We encountered the same difficulty with bearings...several that were "close", but there were so few 64mm bearings made we couldn't find one that was suitable.
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erstwhile owner of just about every 924 variant ever made

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

Well crap that sucks! I don't know if $900 rods are in my budget.

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81 924 N/A

2004 Ranger "Edge"

2005 Mazda 6

MikeJinCO · Posted: Tue Oct 18, 2011 11:41 pm Post subject:

Has anyone checked the early VW diesel or the 5cyl Audi's? They aren't in the ARP catalog. Going to the VW tuners might be the way to go. I don't have any rods or I'd send one to Techtonics for a start.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

MikeJinCO · Posted: Tue Oct 18, 2011 11:52 pm Post subject:

Mispost, ARO does have MkI VW bolts on the Techtonics website. But nothing for the Audi 5cyl.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

FWIW, rumor has it that European Motorworks developed their stroker based on a VW rod with smaller big end journals and flat top pistons, but I've not been successful in documenting exactly what they used. I can tell you one thing, I am extremely skeptical about the claimed 2.4L displacement...it would require a whopping increase to the stroke, and even with my custom Crower rods, there was still very very tight clearance on the front two rods (at the shoulders) due to one of the oil galleys.

If you go to my downloads page, you will find an Excel spreadsheet compiled by our own Peter Barnett listing out critical rod dimensions for many applications. This is a good place to start if you're looking for ideas on alternate rods.

One of the most critical things to be aware of is that the OEM rods are crank-centered, meaning that the ideal replacement would have a big-end width that is identical to the stock unit. If you find one that is just slightly larger, it could be machined down, but if it is smaller to begin with, you would have to add material and then machine it back down. Which in my opinion sort of defeats the purpose. Smaller big end diameter would also be desireable, so that you could use the stock rod bearings for the replacement application and simply grind down the stock crank to match. Rod length and pin diameter are not as critical either, assuming you were going to use custom pistons, because the pistons could be designed to accommodate any variance from OEM dimensions.

Having said all of that, what you're going to find by looking at that excel spreadsheet, is that the OEM big end width of 27.9mm is unique to the 924. There are no rods listed in that sheet that match this dimension, and this is a challenge (if not a show stopper) that you will have to overcome somehow, both in terms of the rod itself and its bearings.
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erstwhile owner of just about every 924 variant ever made

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

What you would have to do is use the rod and piston from another car... the Honda H22 seems like a possible choice the rod is just a little bit shorter and it has a smaller big big.

http://www.exospeed.com/store/index.php?main_page=index&cPath=211_196_68_126_182_129_194

http://www.crower.com/billet-crowerods-honda-prelude-2-2-vtec.html
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81 924 N/A

2004 Ranger "Edge"

2005 Mazda 6

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

A smaller big end will require grinding the crank journals to match. The key dimension, however, is not the diameter, it is the width of the rod, or what in machinist-speak is referred to as the "length" of the bearing. Used in this context, "length" is somewhat counter-intuitive...but that's what bearing specs list as the dimension that one would normally think of as being the cross-sectional width of the rod, i.e. when looking at it from the side. As noted above, OEM rods are crank-centered, meaning that the shape of the journal and the rod are what hold the rod in place and keep it from slapping back and forth on the journal surface. If you look at a piston-rod assembly, you will see that there are gaps on either side of the little end of the rod when attached to the piston.

Using a shorter rod means that you will need a different piston than OEM because the lower pin height will reduce CR. So you will either need custom pistons designed to make up for the difference in pin height, or you will need to find an off-the-shelf piston that will result in roughly the same compression height as the OEM piston. More variables.

If you opted for a custom piston, you could have it designed so that the rod was "pin-centered", meaning that the bosses thru which the piston pin are held would be machined precisely to hold the rod in place, rather than having it be crank-centered. This would probably require having an entire rotating assembly available to the piston manufacturer so they could take the necessary measurements to make sure that the rod was appropriately positioned at the pin so as to be roughly centered on the crank journal.
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erstwhile owner of just about every 924 variant ever made

the_mad_electrician · Joined: 16 Nov 2009 Posts: 1073 Location: Central Georgia

The honda is piston centered, I have some friends that are into hondas trying to get me a used rod or at least the width measurment. I just got the idea from an engine build I saw where a guy used Subaru pistons for a stroked chevy 307. Very interesting build..
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81 924 N/A

2004 Ranger "Edge"

2005 Mazda 6