90 degree V6 3 throw crank project

[F1fan01]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.

However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.

The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.

I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.

The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.

I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.

Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

[Tommy Cookers]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.
However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.
The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.
I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.
The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.
I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.
Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

er well ...... and broadly .....

firing order is nothing to do with firing intervals
(there's anyway only 1 firing order with a 3 pin - 2 orders if one bank has internal different order to the other bank)

vibration is to do with inertia forces ie rpm not gas loads ie firing
(the 1960s GM 90 deg 3 pin-ers never had a real vibration problem - people inferred vibration from the uneven sound)
there is no magic bank angle for zero vibration on a 3 pin V6 (a 6pin V6 gets good when the bank angle nears 180 deg)

a 90 deg V twin uses counterweights big enough to cancel primary force vibration (but not the large secondary force)
so a 90 deg V6 could be made with a 'single' pin 'flat' (longitudinally symmetric) crankshaft to use these CWs
and similarly both a 3 pin 'flat' crankshaft (as Laverda 3) and a 3 pin 2 plane @ 90 deg are quite good
but further counterbalances are needed as the basic layout of all these shafts is itself unbalanced
heavy CWs tend to depress torsional vibration frequencies
normal 3 pin V6s (little CW) have force balance but even 120deg bank angles give primary&secondary moment imbalances

most current road V6s are (60 deg) 6 pin with some very slender webs so the engines are no longer than a 3 pin-er
(NOTE to self - this I wrote on p7 of the thread 'engine block aluminium vs CGIron)

[vvillium3]

The safe view on this is yes, the vibrations may become a problem. Key word, being may.

Even if the engine cylinder count and layout results in a perfect first and second order balance. The engine can still have serious vibration issues. The crankshaft, camshafts, timing chains, etc. are just expensive springs. They all bend and stretch in different ways when loaded by different forces that happen in a running engine. The worst being the natural frequency of a component that an engine operates in regularly. Hence the great amount of effort that goes into engine designs to dampen these issues out.

So in short yes, changing a crankshaft layout can affect the vibrations, just not in the way most generally speak. It may not seem like you're changing much, but a little bit may make just enough of a difference.

However, don't let this deter you from the project. You may get lucky and see no issues and the stock damper my work perfectly for your new crankshaft design. Just do your homework and learn about this stuff before paying to have a one off crankshaft machined up. There are tons of great books out there that can be had cheap. It'll be a great opportunity for a learning experience.

[Piscine]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.
However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.
The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.
I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.
The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.
I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.
Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

a 90 deg V twin uses counterweights big enough to cancel primary force vibration (but not the large secondary force)
so a 90 deg V6 could be made with a 'single' pin 'flat' (longitudinally symmetric) crankshaft to use these CWs
and similarly both a 3 pin 'flat' crankshaft (as Laverda 3) and a 3 pin 2 plane @ 90 deg are quite good
but further counterbalances are needed as the basic layout of all these shafts is itself unbalanced
heavy CWs tend to depress torsional vibration frequencies
normal 3 pin V6s (little CW) have force balance but even 120deg bank angles give primary&secondary moment imbalances

Not sure how I missed this thread, but I've actually had to do quite a bit of research on this very subject as I've been rebuilding an awful lot of Maserati Merak/Citroen SM engines lately. I've also developed a 3.3L stroked engine (92mm x 82mm), different cams, lots of compression, H-beam rods, the works. The 3.3L engines I've built using 44DCNF carburetors are making between 270-280hp and the 48IDA carbureted engines make 300hp+, all in road trim with friendly road manners. I've yet to build an all-out race motor but that is in the works as I am building a spare engine for the 1973 Ligier JS2 which finished Lemans in the hands of Delaland. The Lemans Ligier JS2 and Michelin sport proto Citroen SM (breadvan) were the only engines to use the 48IDA manifold until I developed one again, which truly transforms these engines.

What I learned from old Maserati historians who knew Alfieri was that he was concerned about the secondary imbalance issue due to the quality and strength of components at the time. They needed the engine to last at least some time (warranty period or so) and the cast pistons and rods were in question. Secondary imbalance is also present in 4 cylinder engines, but the V6, given the individual cylinder capacity for this Maser engine was of concern. Maserati actually went through 3 or 4 different connecting rod designs, each beefier than the last specifically at the small end just under the pin. The stock cast pistons still sometimes detonated at the pin casting area.

Anyway, with modern components the secondary imbalance concerns are a thing of the past which is why we see the Alfa Romeo Quad. and Nettuno engines, and several other odd-fire V6 engines rebirthed. Even the MG 6r4 motor was of course the same design but used strong forged components so the secondary imbalance concern was a non issue even then. F1 knows the severity of secondary imbalance is directly related to the weight of the reciprocating components, so considering how incredibly light their components are I'm sure it's not an issue.


The below is from my humble channel documenting one of the 3.3L builds where I cover some of these points. I absolutely love these 3 pinner Maser engines now

[BassVirolla]

V6 90 degree engines have split crank journals for even firing intervals 120 degree for a smoother engine.
However there are success stories like the current F1 V6 with 3 throw cranks with odd firing order.
The benefits of a stronger shared pin (3 pin crank) albeit with an odd firing order makes it a lighter and strong bottom end.
I’ve seen posts suggesting that odd fire shared pin engines not suffering from vibration issues once it revs out.
The new Maserati Nettuno engine is a modern 3 pin v6 90 degree with Odd fire 1-6-3-4-2-5 order.
I am contemplating rebuilding an engine with a 3 pin crank which necessitates an odd fire setup from its original even fire configuration.
Would the valve train or harmonics become a problem with this switch? Assuming the engine will rev from 4000-9000rpm most of the time?

a 90 deg V twin uses counterweights big enough to cancel primary force vibration (but not the large secondary force)
so a 90 deg V6 could be made with a 'single' pin 'flat' (longitudinally symmetric) crankshaft to use these CWs
and similarly both a 3 pin 'flat' crankshaft (as Laverda 3) and a 3 pin 2 plane @ 90 deg are quite good
but further counterbalances are needed as the basic layout of all these shafts is itself unbalanced
heavy CWs tend to depress torsional vibration frequencies
normal 3 pin V6s (little CW) have force balance but even 120deg bank angles give primary&secondary moment imbalances

Not sure how I missed this thread, but I've actually had to do quite a bit of research on this very subject as I've been rebuilding an awful lot of Maserati Merak/Citroen SM engines lately. I've also developed a 3.3L stroked engine (92mm x 82mm), different cams, lots of compression, H-beam rods, the works. The 3.3L engines I've built using 44DCNF carburetors are making between 270-280hp and the 48IDA carbureted engines make 300hp+, all in road trim with friendly road manners. I've yet to build an all-out race motor but that is in the works as I am building a spare engine for the 1973 Ligier JS2 which finished Lemans in the hands of Delaland. The Lemans Ligier JS2 and Michelin sport proto Citroen SM (breadvan) were the only engines to use the 48IDA manifold until I developed one again, which truly transforms these engines.

What I learned from old Maserati historians who knew Alfieri was that he was concerned about the secondary imbalance issue due to the quality and strength of components at the time. They needed the engine to last at least some time (warranty period or so) and the cast pistons and rods were in question. Secondary imbalance is also present in 4 cylinder engines, but the V6, given the individual cylinder capacity for this Maser engine was of concern. Maserati actually went through 3 or 4 different connecting rod designs, each beefier than the last specifically at the small end just under the pin. The stock cast pistons still sometimes detonated at the pin casting area.

Anyway, with modern components the secondary imbalance concerns are a thing of the past which is why we see the Alfa Romeo Quad. and Nettuno engines, and several other odd-fire V6 engines rebirthed. Even the MG 6r4 motor was of course the same design but used strong forged components so the secondary imbalance concern was a non issue even then. F1 knows the severity of secondary imbalance is directly related to the weight of the reciprocating components, so considering how incredibly light their components are I'm sure it's not an issue.


The below is from my humble channel documenting one of the 3.3L builds where I cover some of these points. I absolutely love these 3 pinner Maser engines now

I love it! If I could afford it, I would love to get through the hassle of owning an SM.

[Greg Locock]

In 42 years I estimate I have spent at least 6 years working on serious projects intended for production that got abandoned. One of them was a 90 degree V6. Absolutely bloody awful engine with no redeeming features (except, I suppose, cost and perhaps packaging).

My biggest problem was various imbalance forces (1.5 order I think) that made designing a good set of engine mounts impossible (at the time) that was compatible with the original body, which usually had an I6. Since this was for a BMW 535 competitor NVH was important.

[Piscine]

In 42 years I estimate I have spent at least 6 years working on serious projects intended for production that got abandoned. One of them was a 90 degree V6. Absolutely bloody awful engine with no redeeming features (except, I suppose, cost and perhaps packaging).

My biggest problem was various imbalance forces (1.5 order I think) that made designing a good set of engine mounts impossible (at the time) that was compatible with the original body, which usually had an I6. Since this was for a BMW 535 competitor NVH was important.

Agree, the issue was materials at the time, it was an engine that couldn't possibly make sense with what was available.

You note the 1.5 order imbalance, is that better or worse than a 4 cylinder engine? probably worse.... The SM crankshaft used only 4 primary balance throws while the later SS crank used 6, they must have learned

[Greg Locock]

I can't remember exactly what was wrong with it, I think there may have been a pitch/yaw rocking couple. I don't think it was worse than an I4, but since it was competing with an I6 that is not the issue.

Engine mounting was a black art in the 80s - major manufacturers cancelled programs because they couldn't mount their engines. XJS spent a year or two running on chassis dynos with the rear of the gearbox on a jack as the design of the gearbox mount was being developed. One major program at BL was built with two different engine mounting strategies. etc.