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LD28 3.1 engine build


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7 hours ago, madkaw said:

 

5 hours ago, calZ said:

A whole lot of whirrrrrrrrr

Ah, we're talking about the twin idler, I thought you were hinting the longer chain would be different! 

I've has it for years on the previous couple of engines. I love it. 

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10 hours ago, grannyknot said:

Sorry, I assume everyone has an RT mount for the diff. and as Madkaw suggests, it is possible.  I modified the front diff xmember so I could drop the front of the diff 3/4" and then stacked some washers under the snubber.

The pics below were in the mock up stage but you get the idea.

 

DSCN0627.JPG

DSCN0628.JPG

thats a fair bit of work. did you have to lower the rear arm mounts too? 

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5 hours ago, AydinZ71 said:

I’d love if someone could explain the purpose or advantage of the twin idler. I think it’s cool as hell. If it doesn’t serve a functional purpose though, I don’t think I would get it for the race engine. That noise indicates it is adding friction/resistance to the engine but I’m sure there is an up side! Does it keep the chain from fking up at high rpm? 

 

It has been discussed many times over the years on this and other forums, but the Twin Idler chain tensioner was created (by Shigeo Mori and Kameari Engine Works) to address issues related to chain whip and consequential variance in cam timing - especially during rapid off-throttle engine deceleration. He found that in some circumstances the chain whip was so severe that it completely overcame the stock tensioner and the camshaft was out of phase with the crankshaft to a degree where pistons were kissing valves.

 

The stock oil pressure-powered 'shoe' tensioner in these engines was a compromise in any case. The *original* L-series tensioner design was an adjustable idler, and that 'inspection cover' on the front of the cylinder head (which the top parts of the Kameari Twin Idler is designed to fit into) is an artefact of that original design. It was sacrificed to NVH and servicing longevity. The oil pressure-powered shoe and rubber-faced guides work very well for road cars and can be blueprinted for race use, but anyone who is worried about friction issues with the Twin Idler might be well advised to consider the amount of friction in the stock system...

 

So the Twin Idler maintains the all-important phasing relationship between the crankshaft and the camshaft at all times, but also has the spin-off benefit of allowing correct chain tension to be built into engines that have had cylinder head/block face skims and would otherwise require cam tower shimming, which is less than ideal.

 



           

L20-six-chain-1.jpg

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41 minutes ago, HS30-H said:

The stock oil pressure-powered 'shoe' tensioner

During the design phase on the KN20 I did a lot of research into timing chain designs. I did some calculating on what kind of pressures the tensioners were delivering. In a perfect world a .567'  (14.5mm) diameter rodless hydraulic cylinder will deliver just over 17 pounds of force at 70 psi. I measured a few springs from tensioners and they were all in the 14-15 pound range in their operating position.  So there really isn't a lot of force provided.  Also I think tensioners for all practical purposes are spring driven and oil oil dampened since anything under 70 psi the spring is delivering more force than the oil pressure. 

 

Chain sprockets are a polygon and suffer from what's called polygon effect. When the chain exits a sprocket it induces whip. The smaller the sprocket diameter the bigger the effect. I think that is why bottom pivoting slack side guides became the norm. Much more surface area to control the polygon effect as well as a faster response time when the engine goes into overrun since that happens at the top of the guide where the tensioner is. 

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I think the cool factor outweighs any reasonable longevity argument -LOL. 

It sure does make the process of getting our cam dialed in much easier . You can literally go either direction with the chain instead of just one direction. Time will tell about adverse wear issues .

Love the instructions that came with the tensioner -

"please ignore bearing noise-this is normal" 

My exhaust is pretty loud so Imagine if the exhaust was quieter , the tensioner would be more obnoxious .

As stated before -don't over tighten. Just use your fingers to press the gears together.      

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8 hours ago, Derek said:

During the design phase on the KN20 I did a lot of research into timing chain designs. I did some calculating on what kind of pressures the tensioners were delivering. In a perfect world a .567'  (14.5mm) diameter rodless hydraulic cylinder will deliver just over 17 pounds of force at 70 psi. I measured a few springs from tensioners and they were all in the 14-15 pound range in their operating position.  So there really isn't a lot of force provided.  Also I think tensioners for all practical purposes are spring driven and oil oil dampened since anything under 70 psi the spring is delivering more force than the oil pressure. 

 

Chain sprockets are a polygon and suffer from what's called polygon effect. When the chain exits a sprocket it induces whip. The smaller the sprocket diameter the bigger the effect. I think that is why bottom pivoting slack side guides became the norm. Much more surface area to control the polygon effect as well as a faster response time when the engine goes into overrun since that happens at the top of the guide where the tensioner is. 

surely an idler sprocket isn't going to impose much speed variation on the chain - it'll be completely dominated by the driving and driven sprockets, so wouldn't the polygon effect mean the idler sprocket speed varies instead? 

the term and concept is brand new to me, so I could be completely wrong. 

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My understanding of the polygon effect was it induced instability (whip) as it exited the sprocket. The smaller the sprocket the more instability. So you have a whip in the chain at the bottom coming up all the time.  Couple that with the dynamics induced during overrun conditions and you can see controlling a timing chain can be tough. Now change the dynamics again with different lifts and lobe offsets and chain wear and breakage comes into play.  The tension system is as much a dampening system as it is anything else.

 

I'm sounding doom and gloom but I think when people make changes to the timing chain system they should be aware of what they are dealing with.  There are ton's of people running those twin idlers without a single issue so there's that. Plus it's not like anyone is going to be putting 100K miles on these cars anymore.

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2 hours ago, Derek said:

My understanding of the polygon effect was it induced instability (whip) as it exited the sprocket. The smaller the sprocket the more instability. So you have a whip in the chain at the bottom coming up all the time.  Couple that with the dynamics induced during overrun conditions and you can see controlling a timing chain can be tough. Now change the dynamics again with different lifts and lobe offsets and chain wear and breakage comes into play.  The tension system is as much a dampening system as it is anything else.

 

I'm sounding doom and gloom but I think when people make changes to the timing chain system they should be aware of what they are dealing with.  There are ton's of people running those twin idlers without a single issue so there's that. Plus it's not like anyone is going to be putting 100K miles on these cars anymore.

I think you underestimating the BLING factor. It comes in different colors

Most of us won't drive our cars enough to test the limits of everyday driving on this tensioner . It was worth to me just to make dialing in the cam easy and or turning over the motor . Really came in handy with a P90 shaved .080

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Thanks for all the input! I didn’t mean to hijack the thread and cause so much controversy 😂 

 

I asked a few folks I know off-forum who race L-series, and they are aware of but don’t run the twin idler. Greg Ira for instance just moves the curved static chain guide to eliminate slack. They do however speak highly of the Kameari cam timing sprocket for its limitless adjustability. You would need to dyno the engine to get the most out of it if course, especially with a wild profile. 
 

thanks everyone for your input!! And sorry again to the OP 

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On 6/3/2021 at 12:59 AM, AydinZ71 said:

I asked a few folks I know off-forum who race L-series, and they are aware of but don’t run the twin idler. Greg Ira for instance just moves the curved static chain guide to eliminate slack.

 

 

There are plenty of K.E.W. Twin Idlers in race (and rally) use, and there have been for many years.

 

A wise head once remarked to me that the incessant drone of 'for' and 'against' from the sidelines easily drowns out the mild gear whine from a properly adjusted Twin Idler...  

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6 hours ago, HS30-H said:

 

There are plenty of K.E.W. Twin Idlers in race (and rally) use, and there have been for many years.

 

A wise head once remarked to me that the incessant drone of 'for' and 'against' from the sidelines easily drowns out the mild gear whine from a properly adjusted Twin Idler...  


I need to visit the chiropractor. My twin-idler gears are whining louder than normal recently. 

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  • 3 weeks later...

Progress is delayed. I hadn't noticed the bead on the gasket is just outside the block where the coolant bypass is on a petrol block, and I had a leak when I assembled it. 

I've built the block out with a spot of epoxy putty to give the bead something to sit on. 

No idea how long it will hold, but tomorrow should be first start. 

 

DSC_0005.JPG.14227b7e9d7313a68fa96947e90df3de.JPGDSC_0007.JPG.82c9a02c90d2b2cb3acb79fc1f67c437.JPG

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