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ARP Rod Bolts Group buy?
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1983
Location: Somerset, UK

PostPosted: Sat Dec 14, 2019 7:01 pm    Post subject: Reply with quote

safe wrote:
Its NEVER cheep to properly rebuild an engine, regardless the cost of the vehicle.
This is the downfall of the 924, it costs $1000 so the hillbilly who owns it doesn't want to by 4 new good tires, he buys 3 different kind of used tires. A relay fails, that costs money, he has a switch left over from a tractor. Lets put that in, lets drill a hole in the dash for it... etc.
Soon this car is a pile of junk tons of "customisations" that gets left in a field to rust away.



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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Then www.924board.org/viewtopic.php?t=31252
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safe  



Joined: 18 Mar 2017
Posts: 166
Location: Sweden

PostPosted: Sat Dec 14, 2019 7:53 pm    Post subject: Reply with quote

Fasteddie313 wrote:
safe wrote:
Lighter pistons would be better over all for the engine.


My problem is that I would need bolts in order to change the pistons in any 2.0 shortblock.. Be it my current block, or more likely the replacement when I finally blow mine up..

Might be cheapest just to find another 931 engine to blow up, or a 2.0 shortblock if my head survives the inevitable catastrophy, but would need the pistons replaced, thereby requiring new rod bolts $$..

This just seems ridiculous money for some bolts.. Head studs are half the price..

We already know a lot can be ground off our rods to save weight and they are still plenty strong..
Why can't we find some more available and sanely priced bolts to do the job, and possibly even modify the rods to work with them?



The rods could possibly be reemed to take a slightly larger diamiter bolt?
The rods could possibly be modified where the head of the bolt meets the rod?

ideola wrote:
M10x1.0 Porsche Rod Bolt


They are 10mm dia?

What is so complicated about finding bolts to fit these holes?

BMW M10 rod bolts are 10mm
https://www.summitracing.com/parts/arp-201-6304/overview/
$108

Too short? Take some material off the rods so they fit?

10mm=0.393701"
7/16"=11.1125mm
Ream the holes out to 7/16?

49 results of cheap rod bolts in 7/16..
https://www.summitracing.com/search/part-type/connecting-rod-bolts/thread-size/7-16-in?N=thread-size%3A7-16-in&SortBy=Default&SortOrder=Default

ARP has all sorts of 10mm bolts..
https://arp-bolts.com/kits/bulk.php?PL=89&M=2&W=*&D=8&P=15&WS=13

Can't make anything fit?



Anything made in small batches will be silly expensive. If ARP had something that would fit straight on, like the head studs do, they would just sell you that. I think its almost crazy that they would just 10 sets.

Modifying the rods foe a "standard" ARP bolt, its interesting but way out my comfort zone both skill and tool vise. Its not some job for a drill press and a grinder.
A rod bolt is not just a bolt, there is a reason the fit of the bolt is really tight, it guides and locate the rod cap very precisely.
A machine shop could probably do it but what would the cost be?

If the rpm is kept to the stock rev limiter I would be much much more comfortable with reusing the so called one time use stock bolts.

The price for 931s will rise. In Europe you find rough ones below $10000, really nice ones are closer to double that.
Money invested properly in a 931 will pay back.
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TJC  



Joined: 04 Apr 2010
Posts: 754
Location: Central-ish Arizona, USA

PostPosted: Sun Dec 15, 2019 1:52 am    Post subject: Reply with quote

Fasteddie313 wrote:
safe wrote:
Lighter pistons would be better over all for the engine.


My problem is that I would need bolts in order to change the pistons in any 2.0 shortblock.. Be it my current block, or more likely the replacement when I finally blow mine up..

Might be cheapest just to find another 931 engine to blow up, or a 2.0 shortblock if my head survives the inevitable catastrophy, but would need the pistons replaced, thereby requiring new rod bolts $$..

This just seems ridiculous money for some bolts.. Head studs are half the price..

We already know a lot can be ground off our rods to save weight and they are still plenty strong..
Why can't we find some more available and sanely priced bolts to do the job, and possibly even modify the rods to work with them?



The rods could possibly be reemed to take a slightly larger diamiter bolt?
The rods could possibly be modified where the head of the bolt meets the rod?

ideola wrote:
M10x1.0 Porsche Rod Bolt


They are 10mm dia?

What is so complicated about finding bolts to fit these holes?

BMW M10 rod bolts are 10mm
https://www.summitracing.com/parts/arp-201-6304/overview/
$108

Too short? Take some material off the rods so they fit?

10mm=0.393701"
7/16"=11.1125mm
Ream the holes out to 7/16?

49 results of cheap rod bolts in 7/16..
https://www.summitracing.com/search/part-type/connecting-rod-bolts/thread-size/7-16-in?N=thread-size%3A7-16-in&SortBy=Default&SortOrder=Default

ARP has all sorts of 10mm bolts..
https://arp-bolts.com/kits/bulk.php?PL=89&M=2&W=*&D=8&P=15&WS=13

Can't make anything fit?


This is the kind of thinking that fostered the "hot rod" age from back in the 40's and 50's here in America and I for one applaud it. I have to agree, there probably are other alternatives out there and something that could be explored. As I mentioned in my previous comment there may even be a different rod that could be adapted. On a side note, I have seen many references about the 944 issues with crappy rod bearing availability that has led to modifying the Porsche rod to take a much better bearing that is a Toyota, (I believe), application originally.
Bottom line folks, where there's a will, there's a way !!!
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'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

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MikeJinCO  



Joined: 08 Jun 2010
Posts: 913
Location: Maysville, Colorado

PostPosted: Sun Dec 15, 2019 5:30 am    Post subject: Reply with quote

I have wondered about other bolt use also. I have put out a call to local race group for a BMW bolt to see close it would be, we have 5 or 6 BMW 1600-.2002's around and have several blown motors this year.
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
'77 924
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1992
Location: MI

PostPosted: Sun Dec 15, 2019 6:32 am    Post subject: Reply with quote

M10 bolts are...
Underhead Length (in):2.330 in.
Underhead Length (mm):59.18mm

How long are 924 bolts?



M10= Rod Bolt Head Style:E

What do 924 bolt heads look like?
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924RACR  



Joined: 29 Jul 2001
Posts: 8321
Location: Royal Oak, MI, USA

PostPosted: Sun Dec 15, 2019 8:19 am    Post subject: Reply with quote

924 bolt heads are what I'd consider a very basic round head, like K or W.

Fine, you made me do it... photo album with some very recent pics of rod bots, intact and busted...
https://www.facebook.com/photo.php?fbid=10212999631540325&set=a.10212999625340170&type=3&theater

There's one pic in there that shows just the bolt head, after being snapped off the end of the rod (showing the Kamax 12.9 designation)... and another that, in context, shows the loose bolts.
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 913
Location: Maysville, Colorado

PostPosted: Sun Dec 15, 2019 9:28 am    Post subject: Reply with quote

Measured a used bolt at 65.5mm OA length with a head thickness of 5.0mm.

Read some other sites that said that if switching rod or main bearing bolts the bores must be resized due to the different clamping pressure. I did the calcs and the clamping pressure of the stock bolts at 43 ft lbs torque dry is 431 lb. This based on at measured diameter of 0.3225" on the yield strength of the used grade 12.9 bolt.
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1992
Location: MI

PostPosted: Mon Dec 16, 2019 1:17 am    Post subject: Reply with quote

MikeJinCO wrote:
Measured a used bolt at 65.5mm OA length with a head thickness of 5.0mm.


M10 bolt
Underhead Length (mm):59.18mm

65.5-5=60.5-59.2= difference of M10 bolt = 1.3MM shorter
And your used bolt might even be stretched?

Take 1.3mm off the bottom cap and BAM..
If even necessary..

MikeJinCO wrote:

Read some other sites that said that if switching rod or main bearing bolts the bores must be resized due to the different clamping pressure


If this was true then it would be required for ARP too, no?
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safe  



Joined: 18 Mar 2017
Posts: 166
Location: Sweden

PostPosted: Mon Dec 16, 2019 1:32 am    Post subject: Reply with quote

Fasteddie313 wrote:

If this was true then it would be required for ARP too, no?


You should always check the size and roundness of the big end at full torque on every rebuild. Resize if out of spec.
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safe  



Joined: 18 Mar 2017
Posts: 166
Location: Sweden

PostPosted: Mon Dec 16, 2019 7:06 pm    Post subject: Reply with quote

As reference, the ARP and original are identical, except the stamping on the head. ARP on top.
Edit: Holy sh**, that was huge!.

See pic further down.


Last edited by safe on Tue Dec 17, 2019 2:25 am; edited 1 time in total
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924RACR  



Joined: 29 Jul 2001
Posts: 8321
Location: Royal Oak, MI, USA

PostPosted: Mon Dec 16, 2019 11:44 pm    Post subject: Reply with quote

safe wrote:
Fasteddie313 wrote:

If this was true then it would be required for ARP too, no?


You should always check the size and roundness of the big end at full torque on every rebuild. Resize if out of spec.


Funny, I was just having dinner last night (up here in the frozen north) with a table full of racers, including a past SCCA National Champion, and this exact topic came up; he popped a motor in his (formerly front-running) Prod car at VIR due to exactly this, didn't re-line-bore the mains on his block when he rebuilt it with new ARP main bolts, and spun a rod bearing as a result.

Now I gotta find a local shop that'll do that; the one I've been using doesn't have that tech...
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TJC  



Joined: 04 Apr 2010
Posts: 754
Location: Central-ish Arizona, USA

PostPosted: Tue Dec 17, 2019 1:53 am    Post subject: Reply with quote

Dear safe, please delete and compress your photo and re-submit as every message after it is expanded , LOL!!!
_________________
'95 BMW 318i/5 ..."Pearl"
'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

www.ttrs1.com
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1992
Location: MI

PostPosted: Tue Dec 17, 2019 1:57 am    Post subject: Reply with quote

Well, it probably isn't worth all that just to install upgraded pistons unless your looking for more than 400 hp or so, which I'm not..

Or, might as well buy custom rods, maybe even to fit more available pistons..

Nah.. The OEM stuff will probably hold fine for long enough up to 20-25psi and be plenty fast enough..

safe's pic resized..

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safe  



Joined: 18 Mar 2017
Posts: 166
Location: Sweden

PostPosted: Tue Dec 17, 2019 2:29 am    Post subject: Reply with quote

Fasteddie313 wrote:

safe's pic resized..


Thanks!

Well, for the brave you can go with this:
https://www.aliexpress.com/item/32782381728.html
Fake ARPs included!
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Juho  



Joined: 03 Oct 2018
Posts: 125
Location: Finland

PostPosted: Tue Dec 17, 2019 7:50 am    Post subject: Reply with quote

safe wrote:
Fasteddie313 wrote:

safe's pic resized..


Thanks!

Well, for the brave you can go with this:
https://www.aliexpress.com/item/32782381728.html
Fake ARPs included!



SOMEONE MUST TRY THESE, imagine if they were actually good.
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