ATI Harmonic Dampner on an L20B

[JumboFett]

Hey y'all!

Is anybody out there using an ATI HD on their L20 build? If so, what was your reason (like, what was the threshold that was crossed to justify its necessity), and will the crank pulley bolt to it and remain in alignment with the fan and water pulleys?

Thank you!

[datzenmike]

L20B crankshafts are fully counter weighted and all spinning components (rods, pistons, flywheel and crankshaft) are very well balanced individually at the factory so that parts can be replaced without worry. No I have never used a harmonic balancer because not needed up to the L20B's red line of 7k. I guess if you have one it won't hurt.

[fivetenguy]

Hey Mike, what about the KA's and SR's (NA)?

[JumboFett]

20 minutes ago, datzenmike said:

L20B crankshafts are fully counter weighted and all spinning components (rods, pistons, flywheel and crankshaft) are very well balanced individually at the factory so that parts can be replaced without worry. No I have never used a harmonic balancer because not needed up to the L20B's red line of 7k. I guess if you have one it won't hurt.

Thank you. It’s been 20yrs since I’ve had a Datsun (my 1st car, ‘76 280z), and most of my automotive mechanic experience comes from the world of the SB and BB Chevy engines, so external balance feels like the default. 
 

I just bought a ‘74 620 with an L20B and a 5speed, and I’ve already stepped away from stock with the addition of a Hot-Spark, Weber 32/36, Cannon manifold, and heatshield protected headers. I had big plans for an EFI Rebello motor, but I hear people tend to fall in love with the L20s, so I’m mentally preparing to do a rebuild. I’ve been reading tons of old threads on Ratsun, with a lot of brilliant input given by you, Mike, so I feel like I’ve found the right place.

[datzenmike]

All inline 4 cylinders balance fairly well, second only to the inline 6 which is almost perfect to balance.

[Stoffregen Motorsports]

Full race GT or Production spec L series engines need a harmonic balancer because of the incredible amount of high RPM stress put on the crank. They can come with a cost though. Eary in the KA24 life, we learned that the nose of the crank would break off because of all the added mass, which prompted us to drill through the crank snout almost to the front main bearing area, and then we tapped that hole and ran a super long bolt.

 

What's the threshold? I wouldn't say it's a horsepower rating, but a sustained high RPM thing.

 

For what it's worth, you can fit a 240-260-280Z damper on an L4, but since the pulleys won't line up, you also have to convert to Z car water pump, water pump pulley, etc.

[JumboFett]

8 minutes ago, Stoffregen Motorsports said:

Full race GT or Production spec L series engines need a harmonic balancer because of the incredible amount of high RPM stress put on the crank. They can come with a cost though. Eary in the KA24 life, we learned that the nose of the crank would break off because of all the added mass, which prompted us to drill through the crank snout almost to the front main bearing area, and then we tapped that hole and ran a super long bolt.

 

What's the threshold? I wouldn't say it's a horsepower rating, but a sustained high RPM thing.

 

For what it's worth, you can fit a 240-260-280Z damper on an L4, but since the pulleys won't line up, you also have to convert to Z car water pump, water pump pulley, etc.

Thank you! Considering I’d be limited by the air/fuel flow through the 32/36 I would imagine there wouldn’t be any benefit revving the engine past 6500rpm.

 

Re the 280z pulley notion, could that be a way of fitting a 280z or zx alternator into the system? As long as there’s radiator clearance. 

[datzenmike]

Clearance is a problem on the 620 for upgrading the alternator. The 620 alternator (35 amp and 38 optional) is small in diameter compared to the 50/60 amp car alternators. It has to fit between the block and the frame with the idler arm below it and the radiator hose around and above it. The swing room for adjusting the belt is very limited.

 

To use the larger diameter Nissan 50 amp alternator I fit a Z car lower radiator hose fitting on the timing cover that is more swept back and holds the hose more out of the way and a 720 block mount that lifts the alternator about 1/2" higher. May have used a shorter belt but you had to but the belt on the alternator pulley first then the alternator onto the block mount. If the alternator was on the mount, no way the belt would stretch over the pulley.

[JumboFett]

25 minutes ago, datzenmike said:

Clearance is a problem on the 620 for upgrading the alternator. The 620 alternator (35 amp and 38 optional) is small in diameter compared to the 50/60 amp car alternators. It has to fit between the block and the frame with the idler arm below it and the radiator hose around and above it. The swing room for adjusting the belt is very limited.

 

To use the larger diameter Nissan 50 amp alternator I fit a Z car lower radiator hose fitting on the timing cover that is more swept back and holds the hose more out of the way and a 720 block mount that lifts the alternator about 1/2" higher. May have used a shorter belt but you had to but the belt on the alternator pulley first then the alternator onto the block mount. If the alternator was on the mount, no way the belt would stretch over the pulley.

I did notice that area lacked clearance. Good to know it’s a confirmed problem. My long term plans are to convert the steering to rack & pinion (hoping to find the guidance and exact parts combo in this forum), which might hopefully give me the clearance I need, but that’s a ways away. In the meantime swapping in an internally regulated 60amp alternator would make a huge difference, and would in fact be necessary as my next phase of the project will be to install an American Autowire Highway 15 kit. 

[datzenmike]

Later model Jap cars have high output small diameter alternators. They are also internally regulated so you would have to convert your '74 to get rid of your external regulator. It's easy enough to do.

[JumboFett]

35 minutes ago, datzenmike said:

Later model Jap cars have high output small diameter alternators. They are also internally regulated so you would have to convert your '74 to get rid of your external regulator. It's easy enough to do.

 

Great! I’m definitely down for the cause.

 

Would you happen to have a late-model alternator in mind, and a list of which brackets, pulleys, belts, and any other supporting mods? 
 

Also, thank you all for the input re the dampener. I feel at peace with that matter.

[datzenmike]

I think there was a post on one wire alternators for 620s.