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Discussion Starter · #1 ·
Not really an FAQ, since it goes beyond stock Opel parts, but I though this might be interesting to the engine builders out there. While cleaning up yesterday, I came across numerous sets of connecting rods and thought a comparison was in order. The Crower rods for a Ford 2300 are reasonably cheap, very strong, and only require the big end being narrowed by .013" to fit directly to an Opel crank, Ford bearings and all! The small end was spec'd at .912" pin diameter, and custom shorter pistons can be ordered with the correct compression height to fit perfectly in an Opel engine.
 

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Discussion Starter · #5 ·
Derek Greenwood said:
What combination of pistons could be done with the rods to make a 2.4? A 2.4 out of a 1.9 block with stong rods and so on would be awesome.
With what crank? The rods only affect the rod ratio, not displacement.
 

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Discussion Starter · #6 ·
jeff denton said:
Better yet, just shoot me a price for delivery of four old rods ya found out in the barn. You know what we need. 7500 rpm for up to fifteen minutes of hard left turn, hammer down.
The stock rod on the far left is from my last set of loose stock forged Opel rods. I'm almost done prepping them for shotpeening. Any other stock rods I might have are still in engines, and stored in a trailer far from my barn! I will probably have a set of stock 2.4 rods available when all my projects are through, but one of them is already polished and lightened a bit.

The Crower Sportsman rods look pretty stock from the sides of the beams, but the 'Crower' lettering inside the beam is pretty hard to miss. I suppose you could grind those off, polish lightly, then have them reshotpeened to hide that fact.

Bob
 

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Bob, I was referring to the stroked and bored 2.4 that you drew up using 3.5 pistons. Do you know of a piston to produce this same 2.4 but with the stronger longer rods?
 

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Discussion Starter · #9 ·
Derek Greenwood said:
Bob, I was referring to the stroked and bored 2.4 that you drew up using 3.5 pistons. Do you know of a piston to produce this same 2.4 but with the stronger longer rods?
Nope, they'd have to be custom most likely. Not many engines have a bore that big and a short piston skirt design. Roger Wilson (Roger's Opel Engineering) did a 2.4 conversion last year for a customer of his based on my 1.9>2.4 ideas, but went a step further. He did the Crower rod thing (5.2") and had some custom Venolia forged pistons made.
 

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I was just doing some digging on this subject and found that the Crower rods are offered in 5.2, 5.4, 5.5 and 5.7 lengths for the 2.3. The 5.4 was news to me since the 5.2 was too short and the 5.5 too tall with 2.3 pistons.

I think that 2.4 was planned to run twins. It should be pretty nice when finished.
 

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It looks like we'd better stay with stock rods. They really are good enough for what we're doing, wouldn't you say? To lighten them, do you remove or reduce the pad on the small end, as well as the big end? This is stuff that can be done at home, then a machine shop can resize, shot peen, re-balance, magnaflux, right?
Then again, would you be willing to do them for us and ship us four rods ready to install?
It would be cool to have some custom Rally Bob parts in Speedway GT!
Thanks!!
 

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can opelrods be modified to accept ARP Wavelock Bolts and the like? i was thinking if flattening the top portion and drilling out the threads would work?
 

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Discussion Starter · #13 ·
opelwasp said:
can opelrods be modified to accept ARP Wavelock Bolts and the like? i was thinking if flattening the top portion and drilling out the threads would work?
I think you'd weaken the rod by doing this. So you'd have a stronger bolt and a weaker conn rod! Not a good direction to go....
 

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Discussion Starter · #14 ·
jeff denton said:
It looks like we'd better stay with stock rods. They really are good enough for what we're doing, wouldn't you say? To lighten them, do you remove or reduce the pad on the small end, as well as the big end? This is stuff that can be done at home, then a machine shop can resize, shot peen, re-balance, magnaflux, right?
Then again, would you be willing to do them for us and ship us four rods ready to install?
It would be cool to have some custom Rally Bob parts in Speedway GT!
Thanks!!
Probably not cost effective for me to do it for you.

I'd say that with the power you'll be making and the rpms you'll run, stock forged rods should be okay. Yes, I remove material from both balance pads, as well as other areas on the big end of the rod. Most stock early forged rods are around 625-630 grams, you can comfortably lighten them to 570-575 grams, although I've done some as light as 527 grams!

Bob
 

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LOnger Rods

There are at least two good reasons the 2.4L con rod is 10mm longer (138mm vs 128mm) than the 1.9/2.2L con rod.
1) To keep the piston pin far enough up inside the bore at BDC to maintain piston stability during the "turn around" at the bottom of the stroke.
2) To move the piston high enough up the bore at BDC so that the piston skirt clears the counter weights on the crankshaft without resorting to a much shorter piston.
The longer rod is compensated for by the 2.4L piston having a shorter pin height - with the piston pin being much closer to the piston top than with
the 1.9/2.0L or 2.2L motors.

Half the stroke, plus the rod length, plus the pin height has to come out at close to the block height ( from crankshaft centre line to the deck face ) which is very close to 208mm in ALL the blocks - unless they have been deck-faced shorter........
 

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Discussion Starter · #16 ·
I got around to finishing off the prep work on a set of stock Opel rods. These are for a 'mild' 1959 cc hillclimb engine I'm building.

There is a pretty specific sequence for all the preparation procedures.
First, the rods are magnafluxed to check for any cracks.
Next, the majority of the lightening/grinding is performed (if needed) and they are polished. Most of the rod surfaces are polished down to 180 grit, but the beams are polished in increments ending at 320 grit with the 'grain' of the polishing traveling down the length of the beams, never across.
The next step is the shotpeening, done by an outside vendor.
From there, I discard the old stock rod bolts and run a thread chaser through the bolt holes.
A new set of rod bolts is installed, and then the rods go to the machinist, who resizes the big end of the rods, and hones the small end to size (I am using .912" Ford pins in lieu of factory Opel .907" pins).
The final step is the balancing, which entails not only matching the rods to each other, but each end of the rods are balanced to match the others. This is done on a piece of specialized equipment, basically a hanging scale that ensures repeatability. When all is said and done, they should weigh about 570 grams or so....right now the lightest is at 577 grams after lightening, whereas these stock forged rods weighed 628 grams before the prep work began.

Bob
 

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RallyBob said:
Probably not cost effective for me to do it for you.

I'd say that with the power you'll be making and the rpms you'll run, stock forged rods should be okay. Yes, I remove material from both balance pads, as well as other areas on the big end of the rod. Most stock early forged rods are around 625-630 grams, you can comfortably lighten them to 570-575 grams, although I've done some as light as 527 grams!

Bob
I don't know what restrictions road racing rules put on you but if you want light, strong, no-name to grind off rods, call Mike @ R&R Racing Prods in Grand Park IL (815) 465-6741. Tell him the Stude dude sent you.
 

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Thank you, Studious. What we're doing is running a high bank oval stock car, rules call for stock engine. Well, pretty much stock. "No aftermarket motorsports parts." Some homemade goodies may fly, some alterations to stock parts may be ok, but you gotta be careful. Some parts like camshaft, exhaust system, cooling system can be totally tricked out.
Your rods look nice, Bob. Please tell me just what kind of a grinder/wheel/abrasive tool you use.
Also, when a rod has had a bad day, (spun bearing, ate the crank, turned big end blue) is it considered garbage or "special heat treated"?
 

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RallyBob said:
These are for a 'mild' 1959 cc hillclimb engine I'm building.
I seem to remember that your hillclimb Manta motor was going to be 2.2l based. Have you rethought your approach or is this another project?

-Travis
 

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Discussion Starter · #20 · (Edited)
Travis said:
I seem to remember that your hillclimb Manta motor was going to be 2.2l based. Have you rethought your approach or is this another project?

-Travis
It's a reality check. I have most of the parts for this high compression 1.9 litre, but the 2.2 engine will be built nearly from scratch...and will cost about $6k to build. So I will build the 'cheapie' engine first, and a few years from now when I've accumulated a few more parts I will build the 2.2.

Gotta be realistic with my limited funding, although today I spoke with someone about a job, and that looks pretty good for mid-January startup.
 
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