Topic: Primary Tensioner

[Don R]

 Has anyone ever shimmed the spring on a primary tensioner? I can see a couple different ways to do it, but it seems like a little more tension would help keep the chains in check when rolling off of the throttle.
 I notice Cycle X has an upgraded unit and a stocker with a better spring.

[HondaMan]

FWIW:
Back in my RR'ing days, there were some who went all-in on 'improving' the 750's primary chain tension. I guess it was because they could drop-and-hit the throttle quicker on the [very] tight courses we ran where the 750's bulk was an issue against smaller 2-strokers (with illegally-lightened 750 crankshafts per the rules, but I digress...). Since then I've seen a lot of different ways to do it by separately tensioning the 2 chains while the tensioning of both chains with one roller didn't seem to work as well because the single roller gets torqued sideways from the unequal chains when the mainshaft twists a little at high RPM..

Ken's offering seems similar in principle to several of those home-made versions. The fancier ones had 2 fully separate tensioner arms (which occasionally broke, seemed too small & flimsy?), tensioner rollers in 2 places for the 2 chains (about 1cm apart) each having a separate spring so it could move more (the inner one), stronger springs, etc. Those engines seemed to 'rap' up-down  a bit quicker than other [stock-class racing] engines of the time and one of my friends who rode one said they "felt smoother at revs" than his previous OEM version. As mine was OEM and we pretty much ran neck-and-neck I can't say if it made a difference though?

There's no doubt that the mainshaft twists: that's why the primary chains always grow longer on one than the other.

[PeWe]

The improved tensioner was needed when the chains had got a little more slack?

The chains my K6 has do not want to extend themselves.
Classic Cycle City Heavy duty chains.

Last time  I measured the slack May 2023 only 65.4 mm after a total use of 45000 km.
Same slack measured  2021 and 2020 too.
Most of the time +100whp.
Slack was just under 65.0mm when mounted, before start.
I guess the +0.5mm slack happened direct after startup of engine winter 2013-2014.

These chains a good investment, no need to open the cases for chain replacement.

My K2 has weaker chains but still stronger than Honda stock.  Car timing chains in correct number of links, 68.
65.45mm slack after +14000km

Those chains look like CycleX chains with the strange holes.
Fits several cars, here is one I ordered chains for.  Need to order 2. I ordered 4, 2 chains for a future build.

BMW 530 d,  184 HP,  [E39],  Production: 1998/08 - 2000/09,  Engine code: M57 D30 (306D1)
Original partno: 11 31 2 248 729

You can find more about prim chains in this thread
http://forums.sohc4.net/index.php/topic,154183.100.html

[Tracksnblades1]

FWIW:
Back in my RR'ing days, there were some who went all-in on 'improving' the 750's primary chain tension. I guess it was because they could drop-and-hit the throttle quicker on the [very] tight courses we ran where the 750's bulk was an issue against smaller 2-strokers (with illegally-lightened 750 crankshafts per the rules, but I digress...). Since then I've seen a lot of different ways to do it by separately tensioning the 2 chains while the tensioning of both chains with one roller didn't seem to work as well because the single roller gets torqued sideways from the unequal chains when the mainshaft twists a little at high RPM..

Ken's offering seems similar in principle to several of those home-made versions. The fancier ones had 2 fully separate tensioner arms (which occasionally broke, seemed too small & flimsy?), tensioner rollers in 2 places for the 2 chains (about 1cm apart) each having a separate spring so it could move more (the inner one), stronger springs, etc. Those engines seemed to 'rap' up-down  a bit quicker than other [stock-class racing] engines of the time and one of my friends who rode one said they "felt smoother at revs" than his previous OEM version. As mine was OEM and we pretty much ran neck-and-neck I can't say if it made a difference though?

There's no doubt that the mainshaft twists: that's why the primary chains always grow longer on one than the other.

Would not running staggered links do the same…

A dual row chain never has staggered links by design…but staggering where the links pivot on side by side chains, especially with a worn chain, should produce a teeter tottering effect with a single roller tensioner. 

I always wondered which harmonics were worse, the higher frequency staggered link plates, or the lower frequency of non staggered links plates “flats” striking the round roller @ 8500+…?

[Tracksnblades1]

And wouldn’t good condition rubber dampeners cause premature wear on one chain since they initially bias the load to a single chain until the engine torque or engine braking compresses them…?

Aligning the purposely slightly staggered teeth of the main shaft's sprockets.

[MRieck]

Has anyone ever shimmed the spring on a primary tensioner? I can see a couple different ways to do it, but it seems like a little more tension would help keep the chains in check when rolling off of the throttle.
 I notice Cycle X has an upgraded unit and a stocker with a better spring.

I have done it a number of times with 1/8" thick bar stock.

[Don R]

Has anyone ever shimmed the spring on a primary tensioner? I can see a couple different ways to do it, but it seems like a little more tension would help keep the chains in check when rolling off of the throttle.
 I notice Cycle X has an upgraded unit and a stocker with a better spring.

I have done it a number of times with 1/8" thick bar stock.

 That's what my prototype is Mike. I considered cutting an old tensioner up for a shim but it's thinner than 1/8" and harder to make.

[PeWe]

Photo of a shimmed stock primary tensioner?
I'm curious how it can be done.

[Don R]

 I made a flat 1/8" steel shim that fits on top of the idler base, under the pivot and goes under the hold-down bolt, that holds the bottom of the spring up 1/8". I'll find an 1/8"  longer bolt. I'll get a pic later today when I make a pretty one L0L.

[MRieck]

I made a flat 1/8" steel shim that fits on top of the idler base, under the pivot and goes under the hold-down bolt, that holds the bottom of the spring up 1/8". I'll find an 1/8"  longer bolt. I'll get a pic later today when I make a pretty one L0L.

Exactly.

[Don R]

 This. I wrote idler, not tensioner, thanks for understanding what I meant. Ignore the fuzz and grunge on it, that one came out of a box of tensioner stuff.

[dragracer]

This. I wrote idler, not tensioner, thanks for understanding what I meant. Ignore the fuzz and grunge on it, that one came out of a box of tensioner stuff.

Very good idea. I may try just welding a bead across the same area to increase tension on the spring instead of fabricating the bar stock set up. Same principle either way. Thanks for the illustration.

[PeWe]

Ok, now I know how it can be done thanks!

[HondaMan]

Yep, Don, that's a crafty way to do it!
I was imagining what I saw done by some roadracers of old: they had shims under the mounting bracket, with the OEM bracket entering the shim's copy of the hole, the crankcase drilled out, and a larger-diameter ring placed over the stub of the pin, entering the lower case that way. A complex way to be sure, but they were good fab guys, too, with mills at their disposal to make cool parts.

[Don R]

  I considered raising the entire tensioner, but didn't want to deal with any other clearance or mounting issues that method may create.