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914World.com _ 914World Garage _ Connecting Rod Orientation
Posted by: BeatNavy Jan 12 2019, 07:03 PM
Ok, may be a stupid question, but this is my first Type 4 assembly, so bear with me:
Is it critical that the connecting rods be oriented a specific way on the crank? I've got the numbers matched (rod to cap) properly, but how critical is it for the numbers to point up when the crank is flat as Raby mentions in his video? I got turned around and realized I oriented at least one differently. In the Wilson book he seems to mention that Type 4 are symmetrical and don't really matter (whereas Type 1 etc. need to have the bump on the rod facing up). If it is critical, I suppose I need new rod bolts now that I've torqued them to spec?
These are H-Beam.
TIA.
Posted by: Mark Henry Jan 12 2019, 09:24 PM
Type 1 it matters as there's an offset on the big end, there's a bump on the stock rod that has to face up. If you're using a T4 stroker crank with T1 rods it matters.
I was always told unmarked symmetrical rod the bearing go tangs down, but honestly it doesn't matter, I just do it out of habit and so it doesn't freak out the next engine builder.
First time I installed M96/97 Carrillo (996) rods I emailed Carrillo and asked if orientation mattered, the reply was a simple "Symmetrical rod, no it doesn't".
ARP rod bolts/nuts can be torqued/reused several times as long as it maintains proper stretch spec. If not ARP I'd email the manufacturer (CB, SCAT) but likely their bolts can be reused as well.
Posted by: BeatNavy Jan 12 2019, 10:01 PM
That is perfect, thank you sir.
They are ARP bolts, but it is good to know that it really doesn't matter as well.
Thanks Mark 
Posted by: mepstein Jan 12 2019, 10:05 PM
Interesting discussion on pelican.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/1012902-rod-bolt-assembly-tips.html
Posted by: Mblizzard Jan 13 2019, 03:35 PM
Type 1 it matters as there's an offset on the big end, there's a bump on the stock rod that has to face up. If you're using a T4 stroker crank with T1 rods it matters.
I was always told unmarked symmetrical rod the bearing go tangs down, but honestly it doesn't matter, I just do it out of habit and so it doesn't freak out the next engine builder.
First time I installed M96/97 Carrillo (996) rods I emailed Carrillo and asked if orientation mattered, the reply was a simple "Symmetrical rod, no it doesn't".
ARP rod bolts/nuts can be torqued/reused several times as long as it maintains proper stretch spec. If not ARP I'd email the manufacturer (CB, SCAT) but likely their bolts can be reused as well.
Which way is UP relative to the rod? Got a set of the Type 4 Stores rods for strokes and T1 journals. Can’t really distinguish an up.
Posted by: BeatNavy Jan 13 2019, 03:48 PM
Up is toward the top of the case, if you lay the crank flat with 1/2 rods sticking out one side and 3/4 out the other like it would be once it's sitting in an upright case. But in my case I installed it vertical and missed the "proper" orientation on the crank.
Posted by: Mark Henry Jan 13 2019, 11:10 PM
Which way is UP relative to the rod? Got a set of the Type 4 Stores rods for strokes and T1 journals. Can’t really distinguish an up.
Been a couple years since I had CB H-beam T1 rods in my hands but IIRC they have the same offset on the big end as a stock T1 rod.
I believe the instruction will say tangs down.
Hold the rod vertical on your stomach looking down top of rod, point the small end straight out and the big end in, the big end offset should be to the right and the tangs should be down.
The offset is big enough to see with your eye, with a straight edge it will be obvious.
The offset centers the rod to the piston.
For a no offset symmetrical rod, it really doesn't matter.
Most builders have OCD so they'll put the tangs down.
Posted by: BeatNavy Jan 14 2019, 06:31 AM
Which way is UP relative to the rod? Got a set of the Type 4 Stores rods for strokes and T1 journals. Can’t really distinguish an up.
Been a couple years since I had CB H-beam T1 rods in my hands but IIRC they have the same offset on the big end as a stock T1 rod.
I believe the instruction will say tangs down.
Hold the rod vertical on your stomach looking down top of rod, point the small end straight out and the big end in, the big end offset should be to the right and the tangs should be down.
The offset is big enough to see with your eye, with a straight edge it will be obvious.
The offset centers the rod to the piston.
For a no offset symmetrical rod, it really doesn't matter.
Most builders have OCD so they'll put the tangs down.
To my untrained eye I don't see a tang or anything distinguishing one side or another on these H-Beams - except the numbers on rod and cap. They look symmetrical to me.
Mike, probably misunderstood your question. I assumed, based on Jake's video, to point the numbers on the rod and cap UP toward top of case -- but he's using stock rods in that video. And again, in Wilson's book he says or suggests T4 is symmetrical and doesn't matter.
Posted by: Mark Henry Jan 14 2019, 09:19 AM
Which way is UP relative to the rod? Got a set of the Type 4 Stores rods for strokes and T1 journals. Can’t really distinguish an up.
Been a couple years since I had CB H-beam T1 rods in my hands but IIRC they have the same offset on the big end as a stock T1 rod.
I believe the instruction will say tangs down.
Hold the rod vertical on your stomach looking down top of rod, point the small end straight out and the big end in, the big end offset should be to the right and the tangs should be down.
The offset is big enough to see with your eye, with a straight edge it will be obvious.
The offset centers the rod to the piston.
For a no offset symmetrical rod, it really doesn't matter.
Most builders have OCD so they'll put the tangs down.
To my untrained eye I don't see a tang or anything distinguishing one side or another on these H-Beams - except the numbers on rod and cap. They look symmetrical to me.
Mike, probably misunderstood your question. I assumed, based on Jake's video, to point the numbers on the rod and cap UP toward top of case -- but he's using stock rods in that video. And again, in Wilson's book he says or suggests T4 is symmetrical and doesn't matter.
The bearing tangs, or should I say the tang grooves inside the big end for the bearing tangs. On a stock T1 rod, if the bump is up the tang grooves are down.
IIRC Type 1 40hp up is the only aircooled VW or porsche that has an offset rod. Ballpark it's about a .050" offset.
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