U20 Damper Alternative??

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Daryl Smith
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U20 Damper Alternative??

Post by Daryl Smith »

This aught to start some discussion...

Considering the propensity with Nissan to 're-use' architecture among engines and transmissions, I've got a couple of questions on the vibration damper for the U20...

1) Was a vibration damper used for the H20 in the Urvan (or other vehicles?) which would fit on the U20 crank? Available somewhere?
2) Has anyone checked if a L18/L20B damper would fit the U20 crank? Or for that matter an SR20 damper, or??
3) Are you guys racing the U20 just using the stock Damper?

And yes, the idea is to improve on the 50 yr old technology used then....

Thanks,
Daryl
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Re: U20 Damper Alternative??

Post by JT68 »

The Urvan used an H20, the crank pulley is a 12303-38710, but I don't know if that is a damper or a simple pulley since it is a non-US auto. You could see if canadian sources can get you one.

The inside diameter on that would be correct for the u20 crank, but the belt offset is most likely incorrect since it was for an H. The U was it's own unique configuration.

No go on the SR (or KA) engines, the crank snout diameter is smaller on those cranks.

Most race cars I know of used the stock damper. You can have them rebuilt for not too much money.

Don't think the performance improvement would be worth the effort for adapting something else. The only purpose of the damper is to eliminate resonance and prevent the crank from breaking. U20 cranks almost never break if the rotating assembly is properly balanced and the OEM damper is used. Extremely rare.

Switching to a plain pulley on a U is likely a bad idea. Hope this helps! jt
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Re: U20 Damper Alternative??

Post by JT68 »

Thread above corrected.

L-series do have the same crank snout diameter so conceivably COULD at least fit on the U20 crank (L28). I'll find an OEM pulley and check to see if the seal OD is the same. Also rotational mass offset and belt groove position, I'll check on those too for yah.

Some of the aftermarket L -dampers are also a much larger diameter than OE, so they may interfere with something.
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Re: U20 Damper Alternative??

Post by sunbeam590 »

I have a H20 in my shed and just plain pulley no damping at all.
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Re: U20 Damper Alternative??

Post by JT68 »

I think also the NapZ like Z22 and Z24 also had harmonic balancers and (going from memory) I think that is the same crank snout as the L20. You could look for a early 720 PU Z22/24 in the junkyards. I don't see many of those around anymore though.

If you stay under 5000 rpms you don't need one so much (like a typical H20). If you are winding it up way past that 6.5,7k+, a harmonic balancer is a very good thing. j
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Re: U20 Damper Alternative??

Post by Daryl Smith »

Thanks all for looking!

I wasn't sure about the diameters, but saw a picture of an L series 6 cyl damper that looked almost the same as the U20 except that the V for the belt was at the back of the damper instead of the front, which would make it easier to line up the water pump pulley and alternator on the stroker I'm building (R16 block, U20 crank - 2065cc).
I know the damper is for the crank harmonics, just don't know if those harmonics effect a pushrod motor valve train more than an overhead cam engine...? It is less about the performance increase and more about less noise and vibration...a smoother engine. I plan on pushing this stroker to the 6500-7000 rpm range...often.
Looking around, ATI only lists one damper for the L16/18/20, at 6.325" OD. Stock is about 5.5" ....there may be clearance issues. Might also make it easier to mount a trigger wheel. And they're not cheap, about $400 or so....

I have a U20 damper, with the trigger wheel mounted...lining up the trigger sensor and belts is a bit of a pain when you're not a machinist!!
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Re: U20 Damper Alternative??

Post by Daryl Smith »

This front seal listing has the H20 listed along with most of the L series engines...?
http://www.ebay.ca/itm/NOK-FRONT-CRANK- ... 1264766204
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Re: U20 Damper Alternative??

Post by JT68 »

Yep, seal is a non-issue, those diameters are good.

When I first read the initial post, I was thinking you were talking one for a U20 literally, but since you are talking about stroker/H20, this could work out, but there are still some issues. I don't see a way to use these on a U20 (and no great reason to).

Most people who do a stroker just use the early R16 crank pulley which lines up with the early WP and alternator position. That's easy and works ok since most strokers run out of steam at about 5.5-6k. They will go higher, but they are off the torque curve for the engine.

Since you are building for hi-rpm, the damper is a really good idea since there will be rpms up there where the crank will be unhappy.

I only had 240z and 280z to compare, but the 240 is promising. It would require a spacer on the crank to move it outboard, but not a very big one - like 1/8"-3/16". That would line up the belt groove with the early WP and alternator position. You would remove the AC compressor portion of the pulley if present (it unbolts).

The 240 is a little larger diameter than the stock pulley, so it may be very close or contact the cross member unless you raise the engine or notch the big crossmember. (the U-damper is a close fit as-is)

The 280z's are too big and they also switched to larger size V-belts than stock roadster.
You might check into those 4-cylinder dampers that I mentioned too, I don't have any of those on-hand.

It still looks to me like the U20 damper would be the easiest to fit (and was designed for the crank). If you put it on, the WP belt will be too far forward for the early WP position, but it looks like the late 1600 WP spacer would move that to the right place. I'll mock it up since I have a 67.5 R16 on the bench at the moment. The alternator would have to be slightly repositioned, but that is comparatively easy.

I can probably source for you a rebuilt U20 damper with trigger wheel for about 500 estimated. I think any of the aftermarket ones are going to cost as much or more and most will be too large in diameter.

I also work with a shop that built race dampers for BMW M-series engines from scratch, so a one-off could be done, but it would be major$$$ - top shelf though.

Daryl what is your timing on getting this one running? I have a few other items for you to tinker/experiment with...will PM. Hope this helps, jt
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Re: U20 Damper Alternative??

Post by Daryl Smith »

Timing? When it's done....Don't really have a deadline, but sooner would be better. The engine is out, so notching that crossmember for clearance is a definite possibility. I am moving forward with the U20 damper, just want to keep my options open...
I did consider having the U20 damper rebuilt with the outer ring flipped so the pulley was closer to the engine.
Have to build a mount for the crank VR sensor. It ended up in an awkward place because the trigger wheel (from a Ford) had holes in it which prevented it going where I would have preferred. A little more difficult and time consuming, but only a little. Wanted to have a 'bolt on' solution rather than bolted through the timing cover like my 1800 engine.

Lining up the alt is easy....I'll look at switching to the earlier pump and see where that gets me for the pump pulley.

" I have a few other items for you to tinker/experiment with...will PM. Hope this helps, jt"
I'm interested, my whole car is an experiment.....I have a set of motorcycle throttle bodies waiting, but also looking at other options.
watching for that pm...

I also think the U20 damper, or any damper, would be worthwhile on all these engines which are run up in rpm, G15, R16, H20 included. I'd think they may be more helpful on the 3 main engines, but I'm no harmonics engineer....
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Re: U20 Damper Alternative??

Post by JT68 »

3 main is definitely the weakest crank, they flex the most and can break at high rpm. They also make the fastest 1600 race engines since they are light.

I did verify that if you use the U20 damper and the late model 1600 WP spacer, the belt will be in alignment for the WP with a R16 block no matter which crank you use.

You would still use the early style 66-67 WP, 66-67 pulley and 66-67 fan. The only 68-70 part you would use is the late model pump spacer (photo attached). As mentioned you would need to relocate the alternator to line up.

I have never seen this combination used, but it would certainly be good to have that damper aboard if you are running over 6k frequently. Have fun. J
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Re: U20 Damper Alternative??

Post by Daryl Smith »

Thanks JT!
I've never used that part, so never considered it. Looks like a great solution!
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Re: U20 Damper Alternative??

Post by JT68 »

(And would need longer fasteners for the WP if using an early block.)

If anyone needs help on the Alt mounts I could do those too since I already build relocation kits.

All this would look totally factory as well...nice
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Re: U20 Damper Alternative??

Post by Daryl Smith »

Interesting article on vibration dampers:
http://www.bhjdynamics.com/downloads/pd ... r_Info.pdf
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Re: U20 Damper Alternative??

Post by Daryl Smith »

Bringing this back to clarify the front seal....

The R16 seal has a 45 mm bore
The U20 seal has a 48 mm bore

Are they the same OD, so the U20 seal fits in the R16 timing cover?
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Re: U20 Damper Alternative??

Post by JT68 »

The ID is the same, the OD is different and the front covers are very different.
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