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Discussion Starter #1
Hi guys,

Right. Today I committed myself to stripping the bike down to get at the spark plugs and measure the valve clearances and hopefully eradicate an oil leak from the rocker box gasket whilst I am at it. It's my first time doing open heart surgery on my beloved. It's a 2001 zx12r by the way, 22500 miles.

So far so good, have got in there! So, measured all the clearances and there are quite a few on the lower gap limit. As they are technically in spec, I'm tempted to leave them be, the bike runs beautifully from the off, just the usual but of choke required if a cold start. My question is, what am I likely to gain by changing the shims? Will it make the bike smoother? Also, where would you shim it too? The max gap or somewhere inbetween the max and min?

I ask because whilst the book says to open the gap up a bit, I was wondering if anybody has any experience in running with tighter gaps/or whether there is likely any damage or power loss if the engine is running apparently fine?

Cheers
Tom
 

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As per what NinjaYorkie says




Here is my 2 pence worth, but as its your bike do them as you want to.

As you're doing the Valve clearances yourself you may as well take your time and set them up to the best you can, so make sure you use a good feeler gauge to accurately measure the gaps. These are the best ones I've found for the job, lots of smaller sizes and you can use 2 to make intermediate sizes.
Draper Expert 19613 Dual-Reading Feeler Gauge.

Remember Shim Size on the zx12 is 9.48 diameter, and the sizes you will probably be needing is 2.00 to 2.50mm so buying the full HotCam kit may not be worth it.
Measure what is in there with a good mechanical micrometer and refit it, write down what it was, do this to them all. Now you can work out what sizes you need and with a bit of luck you may be able to order just the sizes you need or a Refill kit covering the sizes you need.
Set the exhaust to the higher side of tolerance and the inlets to below middle, this way your bike will keep the same amount of power for a lot longer before you start to notice a drop in power. Exhausts close faster than inlets at a rate of about 4 to 1. Best exhaust power gaps are about 27,28 ish, but if you set them to this there going to be on there way out straight away, so set them above this, unless you use you bike on the racetrack only and fine tune valve clearances every 2,000 miles.

Finding shims in Half sizes (Honda) helps for fine tuning so you can get a pair of valve the same or within 2 of each other, doing this reduces the chances of engine ticking.

Here's how I set mine up the other month. They should last another 20,000 miles before I even think about checking them again.

yorkie's ZX-12 B4 MAY 2013
19,555 miles
Shim size 9.48

Exhausts 22 to 31

1 Gap = 20 Shim = 2.46 New Shim = 2.35 New Gap = 31
2 Gap = 21 Shim = 2.48 New Shim = 2.40 New Gap = 29

3 Gap = 23 Shim = 2.48 New Shim = 2.40 New Gap = 31
4 Gap = 20 Shim = 2.46 New Shim = 2.36 New Gap = 30

5 Gap = 18 Shim = 2.51 New Shim = 2.40 New Gap = 29
6 Gap = 25 Shim = 2.43 New Shim = 2.40 New Gap = 28

7 Gap = 18 Shim = 2.46 New Shim = 2.35 New Gap = 29
8 Gap = 18 Shim = 2.42 New Shim = 2.29 New Gap = 31

Inlets 15 to 24

1 Gap = 18 Shim = 2.47 New Shim = same New Gap = 18
2 Gap = 18 Shim = 2.46 New Shim = same New Gap = 18

3 Gap = 18 Shim = 2.46 New Shim = same New Gap = 18
4 Gap = 15 Shim = 2.46 New Shim = 2.43 New Gap = 18

5 Gap = 16 Shim = 2.47 New Shim = 2.45 New Gap = 18
6 Gap = 16 Shim = 2.43 New Shim = 2.40 New Gap = 19

7 Gap = 15 Shim = 2.46 New Shim = 2.43 New Gap = 18
8 Gap = 15 Shim = 2.43 New Shim = 2.40 New Gap = 18

NGK Iridium CR9EIX 3521 X4 Fitted
 

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If you run you clearance`s to the tight side you will make more horsepower.But you will have to adjust them more because your at the minimum spec and you do not want to mushroom those puppies.If your not racing I would set them to the loose side and run the shit out of it for a week then you`ll be set for 20k miles if you don`t race the bike all the time.
 

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I want my valve next to me to open the same time.
If I want top end, I tighten the valve so the event happens sooner.
If I want bottom end grunt, I run a loose valve.

Why tight?? A tight valve opens the exhaust sooner, this causes the even to take place sooner, which means more rpm sooner. And it's all about how fast things happen.

Why loose?? A loose valve is closed longer, so this makes the exhaust stroke last longer before the valve opens. This happens slower in proportion, so there is more grunt at low power than at top power rpm's.

And no, there is no valve adjust about to settle out within a week. It takes literally 1000's of miles before the valve lash moves again, so you just adjust the valves within spec or in the middle of the high and low.

Why not tight? When the valve is tight, it has less heat transfer time to cool the valve down. This cracks the valves, can break off little pie cuts out of the face of the valve = Loss of compression.

Why not loose? When the valve is loose, this is too much cool time. Carbon builds on the valve so it can't burn it off. This causes fuel to be soaked into the carbon, creates hot spots and detonate before the spark lights off the fuel. Carbon builds in the chamber = Higher compression.
 

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Discussion Starter #7
Cheers guys. I actually found Dave potter's guide online and have found it very useful, cracking guide, and if I could shake the mans hand I would! So it looks like I'm going to be doing the shim adjustments then, I just wondered what others are happy running. I was once told by a mechanic that if there's no problems starting, then the valves/clearances were fine, but I don't trust him as far as I could spit him and decided to check them anyways lol.

Gonna go and double check the clearances, measure twice and cut once and all that good stuff. On the side, any tips for measuring inlet and exhaust valve numbers 4 and 5? They are bit of a b***h to get to!
 

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Tom come to the Wales meet and you can shake his hand and buy him a beer.
Hi Tom, yes come along if you are free. Where abouts in Hampshire are you? I did my shims last year so I have some shims here, depending on what sizes you need. If I have them you can swop.:thumbup:
 

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Take it for what it's worth. I could guess the price of the rebuild and what minimum parts failed to fix a 4x4 transfer case on Suburbans, trucks, etc. In other words, there were plenty of failures around the country with this one ring that shatters, slips down the shaft and takes out all the gears that mesh, now grind under load. Factory bulletin comes out to explain about noise under the floorboards after a transfer case rebuild.

What they said to do was to time the hy-vo chain back to the same gear tooth. Why? The chain being thrown back together over any gear teeth would cause noise harmonics due to the new wear pattern.

Segway back to bikes and I applied it to the drive chain at the rear, and now cam sprocket and gears. So the quietrick is to time the link to the tooth of the in/ex/crank sprockets so the bike does not begin to start a new wear pattern, cause even more high spots than normal when working with chains and sprockets, and have a new sound to the engine.

Signed,

NOLTT :evil:
 

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Derailment begins... now.

@Hubz: were the chain driven transfer cases Borg-Warner AND New Process or just one. I've dug around inside of both types: chain drive and counter gear but they were both New Process.
 

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Derailment begins... now.

@Hubz: were the chain driven transfer cases Borg-Warner AND New Process or just one. I've dug around inside of both types: chain drive and counter gear but they were both New Process.
Beats me, hag. It's been over 20 years. But the manual is a reach away. What I remember is the 'model 241': that was easy to do from rack to road test. The gm circlip number in my notes read a 3709352: that clip $hatters, and the cha-ching is let loose inside.
 

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Discussion Starter #14
Hey all,

Just rechecked all my clearances and seem to be pretty much as measured the first time. I do have a query about which cylinder is at tdc in compression though. I am using the service manual and recording the clearances on Dave Potters table. His table suggests that with the camshafts oriented in-ex-in-ex with the 320 mark upwards, that the measuring valves are inlet and exhaust on cylinder 1. Here's the thing, cylinder 4 is in compression in this situation, therefore cannot measure cylinder 1 clearances as the cam lobes are pushing on the valves. This seems to be backed up with the service manual, just wondered if anyone can shed any personal experience on this? Am I looking at something arse about face?
 

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Two pistons up Two pistons down.
On the two pistons up Up One is firing the other exhausting and inleting at same time.
The two down pistons one is sucking air in the other has fired.

You rotate the crank over so you can do the other valves.
 

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Discussion Starter #16
Two pistons up Two pistons down.
On the two pistons up Up One is firing the other exhausting and inleting at same time.
The two down pistons one is sucking air in the other has fired.

You rotate the crank over so you can do the other valves.
Cheers ninjayorkie, but I realise this. It's just the way I read Dave Potters guide I was expecting cylinder 1 to be tdc in compression, not 4. That was what my question was mate. Doesn't matter particularly now anyway as I've checked and found 4 must be in compression.
 

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Sorry I wan't sure.

It doesn't really matter as you have to turn it over to do the others anyway.

Like wise when you put it back together, if the number one was exhausting when you lifted the cams and you rebuild it firing, its not going to make a difference.
 

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It's just the way I read Dave Potters guide I was expecting cylinder 1 to be tdc in compression, not 4. That was what my question was mate. Doesn't matter particularly now anyway as I've checked and found 4 must be in compression.
1. To find any TDC, watch the intake move the valve open. When spring retainer/bucket comes back up, drop a chopstick into the plug hole. When the stick stops moving, consider this TDC. Because the stick will move down past TDC.

2. To know the cylinder is at #1 TDC, the lobes are away from the spark plug hole.

3. To set the valves 'flat-rate' style, you move the the crank one full turn, you'll see #4 lobes stick out toward the exhaust and carb/t-bodies, after you checked 8 valve lashes of 4 intakes, 4 exhausts at the #1's position.

4. To find the other 8 lash positions, that one move found all 16 measurements.

5. To find each individual lash, the crank will be turned 4 times you swap back and forth between [watching which lobes are] away from center of the head.
 

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Cheers guys. I actually found Dave potter's guide online and have found it very useful, cracking guide, and if I could shake the mans hand I would!
Consider your hand shook. ;-)

Glad it's helped you and other's out.
 

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I was once told by a mechanic that if there's no problems starting, then the valves/clearances were fine, but I don't trust him as far as I could spit him and decided to check them anyways lol.

Gonna go and double check the clearances, measure twice and cut once and all that good stuff. On the side, any tips for measuring inlet and exhaust valve numbers 4 and 5? They are bit of a b***h to get to!
The mechanic that told you if there are no problems starting the valve clearance is fine needs to get a job selling shoes. He doesn't have a clue what he is talking about.

Like I said in the doc - it greatly helps to have both short and long feeler gauges. And yes, they are a pain to get to.
 
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