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4k Timing chain


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Greetings, KE70 with stock 4k and stock carby in it, done conversion timing chain kit from single row to double row due to chain guide and tensioner wear out, drive smooth but felt when push to higher rev it doesn't as quick as before, chain timing mark and sprocket all in spec according to repair manual, done adjust ignition timing now running 12 degree(sweet spot for my little K's), I was currious is it related to rotational mass due to weight different of single row and double row. Thanks

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I'm not questioning that you've noticed a difference, in the performance, but there could be a couple of reasons, which may not be related to the timing chain at all.

1.  Did you ensure the little location pin between the back of the camshaft sproket & the front of the camshaft was reinstated, when you fitted the sproket to the camshaft ?

The crankshaft sproket has a giant keyway, that locates crankshaft pulley & the timing chain sprocket.  The camshaft sprocket does not have a key, but a pin, that it relys on totally to lock the camshaft & chain, in the correct position.  There have been those on here, that have had this pin shear, with dramatic results. 

2.  Did you replace the tensioner at the same time, as I assume you had a kit with it in ?

3.  It could be that with the sloppy old chain, & a tensioner not working well; that the timing was out enough to effect the performance slightly, as the cam shaft drives both valves & the distrubutor; & hence has a slight effect on the ignition timing.

It could be that you have to adjust the ignition timing slightly, in both directions, in increments, & see whether it makes any difference.   Have you got a timing light ?   That could throw up the fault, as it will indicate, whether the automatic advance/retard mechanism is working OK.  

Have you got a standard points type distributor ?  Maybe it is time to give that an overhaul ?

Let's know what you find.

Trust this assists.

 

Cheers Banjo

 

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49 minutes ago, Banjo said:

I'm not questioning that you've noticed a difference, in the performance, but there could be a couple of reasons, which may not be related to the timing chain at all.

1.  Did you ensure the little location pin between the back of the camshaft sproket & the front of the camshaft was reinstated, when you fitted the sproket to the camshaft ?

The crankshaft sproket has a giant keyway, that locates crankshaft pulley & the timing chain sprocket.  The camshaft sprocket does not have a key, but a pin, that it relys on totally to lock the camshaft & chain, in the correct position.  There have been those on here, that have had this pin shear, with dramatic results. 

2.  Did you replace the tensioner at the same time, as I assume you had a kit with it in ?

3.  It could be that with the sloppy old chain, & a tensioner not working well; that the timing was out enough to effect the performance slightly, as the cam shaft drives both valves & the distrubutor; & hence has a slight effect on the ignition timing.

It could be that you have to adjust the ignition timing slightly, in both directions, in increments, & see whether it makes any difference.   Have you got a timing light ?   That could throw up the fault, as it will indicate, whether the automatic advance/retard mechanism is working OK.  

Have you got a standard points type distributor ?  Maybe it is time to give that an overhaul ?

Let's know what you find.

Trust this assists.

 

Cheers Banjo

 

Hi Banjo

Ans to no.1= Yes, the camshaft pin and the Camshaft sprocket installed correctly but with a bit of effort to fit in, I was affraid at first when installing the sprocket because it won't fit in easily instead of the old single row one, after compare both of them and measurement found out both same size, so I use a rubber mallet slightly tap to fit in. After done install and correct the timing mark then turn the crank by hand 2 to 3 turn and set it to cylinder 1 compression stroke, recheck the timing and found all mark is align and done set valve clearance as spec.

Ans to no.2= Yes, a Double row chain kit come with Camshaft/Crankshaft sprocket, Timing Chain, Chain Guide, Tensioner set, Gasket and Oil Seals.

Ans to no.3= After install double row timing chain kit, the idle run smoother than before and stable, no more intermittent shaking at idle. About the ignition timing previously the timing was jumping at idle by using a timing light to adjust and approximately set it between 10 to 15 degree, after replace the dizzy from point type to electronic type problem still the same, But now i think i have slove the idling issue, compare to previous it indeed improve at pickup and midrange, but just higher rpm range from 4500 to 6000 not as quick as before with 2nd/3rd gear pull and felt heavy like just climbing up without power ( although it just have 40whp I assume). Currently not much modify, only installed 6AL msd, BPR5EGP spark plug gap to 1.2mm(MSD recommended to enlarge according to CR) to a stock 4k, done adjust ignition timing couple of time to increase every 2 degree advance timing up to 20 degree but found the optimal was 12 degree at idle, above 15 degree engine will hesitate while slight throttle, the vacuum advance was running fine, it will hold and move smoothly, dizzy was hooked to ported vacuum. Running a 4K stock carby. Just currious will the weight difference and rotational mass effect at higher rev range.

Cheers

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"Just curious will the weight difference and rotational mass effect at higher rev range."

Easy enough to check-  Add up the weights of the crankshaft, pistons & conrods, the flywheel, the clutch, the gear shafts & gears, the driveshaft, the c/w & pinion in the diff, the axles and the rear wheels. Say about 100kg, and the timing chain weight difference is 1kg, then you've added 1% extra weight to the rotating mass & will lose 1% performance...

I'd say the valve timing has changed, especially the comment about it gaining low rpm performance and losing high rpm. You could do a Datsun and drill three new holes in your new cam sprocket, all at slightly varying degrees off your zero mark. I think Datto 1600s had two marks and we used to put in two more so we could adjust cam timing at 4 then 8 then 12deg and one tooth was 16deg.

Otherwise, just enjoy the smoothness low down!  Get a high-lift cam cut to 270-275deg and concentrate on the torque under 5000rpm.

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I complete concur with Altezzaclub's conclusion that the extra weight in the mass of the double row camshaft sproket & chain, would have little, or no tangible effect on the total rotational mass load on the engine.

It's good to hear your fitment of the new chain & sprockets has instantly improved the idling & mid range performance of the engine.

It's now simply a matter of finding a way to improve the top end, in that 4500 - 6000 rpm range.

Over the years of "playing" with K Series engines, I've changeed a few timining chains & associated sprockets.  I've never been able to get a complete kit here in Australia, with all the components you listed, as being in yours. I've always had to purchase them indivually.  i did, in recent years replace sprockets & chain on a 5K, & was interested to note that the camshaft sprocket did in fact have three hole in the back sde of it, to fit to the location pin.  I  had never seen this on any other aftermarket double row sprockets I had purchased previously.

I was very tempted to try the alternative position to get the valves to open a little earlier, & see what effect resulted.  Hoewever if it didn't work out; & I had to revert to the standard pin position;  I would have to go & remove everything again, and changing timing chains & sprockets is an absolute pain, with the engine in situ.

There are other simpler ways of maybe improving the top end performance, if it is impeded by something else.

The standard ignition coil is well known to drop off it's output at higher revs.  If you already have a electronic distributor, it is possibly one with the "ignitor" built in.

You could replace your coil with a low impedance "sports type" coil, which will improve the top end performance noticably.

You may however find that the electronic dissy you already have; has an ignitor that may struggle to switch the higher primary current of a performance coil.

A simple way around that, is to use the existing ignitor in your electronic dissy, switch an external heavy duty ignitor,  that will power the sports coil.

If that works, & I'm putting myself out there, & saying it will; then you might even be interested in fitting a programable ignition system, which will not only be able to drive the sport ignition coil, but would allow you to map an ignition advance/retard curve perfectly, to give you the best perfomance possible with the engine, as it is.

I did that to a 4K engine in my daily runabout years ago, & it works perfectly; & I've never touched it since, as it is totally maintenance free. 

https://www.rollaclub.com/board/topic/73743-electronic-distributor/?tab=comments#comment-712657

Cheers Banjo

 

 

 

 

Edited by Banjo
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Could it be the dizzy. The original has been replaced for an electronic version. You often hear that they are not graphed properly to suite the 3 and 4k engines but more for the 5 and 7k engines. It might explain why there is plenty low down but not much up the top. Just an idea

 

Cheers

G

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Hi Graeme,

                   Yes you have something there, that could well be the case.  All the dizzies that appear on ebay, are titled as being suitable for 3K, 4K, & 5K.

image.png.8d931d5e558a42d94a4e60107d40f45b.png

The 5K was only used in commerical Toyota, like vans & forklifts etc.  They are designed for torque, but can be made to rev well, if given the right curve.  I'm a great fan of the 5K, as it is nearly a perfectly "square" engine.  I had one in my KE55 coupe for years, & I got it perculating very well.  Many of the 5Ks here in Australia had hydraulic valve lifters, & were very reliable.  I bought a stripped down 5K a few years ago, for $ 100, from a guy up in Gympie Qld., who had modified it for speedway racing. With good preparation, & balancing, they could easily achieve 8K revs plus.  The bottom end of them was almost unbreakable. 

I know Altezzaclub used to "play" with the springs in dizzies, to change their curve, but there is nothing like a locked up dizzy, using it as a trigger only; & feeding that signal into a progammable ECU, where you can play to your hearts content, with advance & retard curves.  

Cheers Banjo

Edited by Banjo
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