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Too Much Compression... Problem Solved!!!

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2 months ago I bought a 2002 CRF450R. Since being new at riding dirt bikes I assumed that it was normal for it to be hard to kick over and that I would get used to it. It was taking me at least 10 kicks with my full body weight on the kick-starter to get this bike started. I realized something was wrong because my buddy has a 2009 CRF450X and I started it with one easy kick.

So I started digging around the forums here and in my manual. A lot of people said to check my clearances on the auto-decompression assembly. I checked the clearances on all the the valve gaps and the decompression gap and set it all to spec and still nothing!

So this weekend I took my bike to my friends house, who on ThumperTalk, is know as Dust_Devil. We went through all the same procedures as I had done before and still nothing. Then we decided to line up everything (timing marks for the crankshaft, flywheel and cam sprocket). The motor was at TDC, everything was lined up dead on and perfect! But.... There was one problem.... The lobes on the cam were facing towards the front of the bike when they should be facing the rear (the cam shaft was 180 degrees out). I don't know if this is a common mistake, but all I have to say is wow to the previous owner or mechanic who worked on it.

We put it all back together as it SHOULD be and the results were amazing. One easy and smooth kick and it started right up and it rides and responds a whole lot better in every aspect! Its amazing how well a high precision machine runs when its assembled properly.

Dust_Devil Is The Man!!! :busted:

Thanks Bro!

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glad ya got that sorted, always nice to know after the fact when people post threads about fixing a problem.. !

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2 months ago I bought a 2002 CRF450R. Since being new at riding dirt bikes I assumed that it was normal for it to be hard to kick over and that I would get used to it. It was taking me at least 10 kicks with my full body weight on the kick-starter to get this bike started. I realized something was wrong because my buddy has a 2009 CRF450X and I started it with one easy kick.

So I started digging around the forums here and in my manual. A lot of people said to check my clearances on the auto-decompression assembly. I checked the clearances on all the the valve gaps and the decompression gap and set it all to spec and still nothing!

So this weekend I took my bike to my friends house, who on ThumperTalk, is know as Dust_Devil. We went through all the same procedures as I had done before and still nothing. Then we decided to line up everything (timing marks for the crankshaft, flywheel and cam sprocket). The motor was at TDC, everything was lined up dead on and perfect! But.... There was one problem.... The lobes on the cam were facing towards the front of the bike when they should be facing the rear (the cam shaft was 180 degrees out). I don't know if this is a common mistake, but all I have to say is wow to the previous owner or mechanic who worked on it.

We put it all back together as it SHOULD be and the results were amazing. One easy and smooth kick and it started right up and it rides and responds a whole lot better in every aspect! Its amazing how well a high precision machine runs when its assembled properly.

Dust_Devil Is The Man!!! :busted:

Thanks Bro!

It wasn't 180 out it was one tooth off.On a four stroke you have 2 tdc.one is on compression stoke and the other is on exhaust.You where lining the marks up on the wrong stroke.

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Getting the cam off one tooth is a common problem,I've done it a few times and the symptom is usually hard to kick and it doesn't run right.Regardless you spun the cam 180 and it sounds like you got her lined up right.

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Perhaps your right.

But when when we lined up the crank shaft marks, the flywheel "B" mark, and the cam marks the cam lobes were facing forward. So we left the timing exactly how it was, relieved tension off of the timing chain, unbolted the cam sprocket, spun the cam shaft 180 degrees (so the lobes faced towards the back), bolted the cam sprocket back to the cam shaft, etc.

To me that seems to be 180 out, not just a tooth off. But if I am mistaken about it I thank you for the info, I'm trying to learn as much about this bike as I can.

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It wasn't 180 out it was one tooth off.On a four stroke you have 2 tdc.one is on compression stoke and the other is on exhaust.You where lining the marks up on the wrong stroke.

Yes the engine comes to top dead center 2 times. The timing mark on the primary gear and flywheel only align when the engine is at TDC. Everything hinges on the cam being timed at TDC of the compression stroke. To properly time the engine align the marks on the primary and flywheel and then install the cam with the lobes facing rearward, the cam gear mark is the last thing to align. When everything is perfect all three marks align perfectly and the cam's intake lobes are flat and facing the rear of the engine.

Jeremys timing marks (on the primary and flywheel) only aligned perfectly when the engine was at TDC of the exhaust stroke. Flipping the cam 180 degrees solved the problem. It was far from one tooth off.

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Yes the engine comes to top dead center 2 times. The timing mark on the primary gear and flywheel only align when the engine is at TDC. Everything hinges on the cam being timed at TDC of the compression stroke. To properly time the engine align the marks on the primary and flywheel and then install the cam with the lobes facing rearward, the cam gear mark is the last thing to align. When everything is perfect all three marks align perfectly and the cam's intake lobes are flat and facing the rear of the engine.

Jeremys timing marks (on the primary and flywheel) only aligned perfectly when the engine was at TDC of the exhaust stroke. Flipping the cam 180 degrees solved the problem. It was far from one tooth off.

Thanks again Dust_Devil! Once again, your endless supply of knowledge and you ever so large collection of tools has saved the day.

Bicycle. Monkey. Ashy Larry.

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I believe spinning the cam 180 deg.wouldn't matter because the ignition fires on every stroke,so I'm not clear on why it would matter if it was 180 out.

I could be wrong but I thought the compression stroke was determined by the cam position and spinning it 180 would only change the stroke from comp. to exhaust or vise versa.

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Yes the engine comes to top dead center 2 times. The timing mark on the primary gear and flywheel only align when the engine is at TDC. Everything hinges on the cam being timed at TDC of the compression stroke. To properly time the engine align the marks on the primary and flywheel and then install the cam with the lobes facing rearward, the cam gear mark is the last thing to align. When everything is perfect all three marks align perfectly and the cam's intake lobes are flat and facing the rear of the engine.

Jeremys timing marks (on the primary and flywheel) only aligned perfectly when the engine was at TDC of the exhaust stroke. Flipping the cam 180 degrees solved the problem. It was far from one tooth off.

It is not possible to install a cam 180° off in a single cylinder, 4 stroke, engine and have any effect on it's running. The only difficulty would be installing the cam tower due to the spring pressure of the valves.

The engine comes to TDC once every revolution. Whether it is on the compression stroke or exhaust stroke is another story. There is no such thing as two TDC's and a relation to a dot or mark other than the correct mark on the cam sprocket. TDC will always align the dots on the right side because TDC is TDC.

The two gears on the right side engine case (driven gear and balancer gear) are 1:1. The dots on those gears are to have the correct balancer alignment with respect to the counterweights of the crankshaft. They will align every revolution.

One part of your statement it itching at me though... How could the cam align correctly on the exhaust stroke and not the intake stroke.... Somehow I am thinking cam chain tension... Because, mechanically, a gear ratio of 2:1 is 2:1 no matter what!

It sounds like the cam tower was installed by forcing the bolts down because of spring tension against the lobes!

The chain was being pulled to one side and what looked to be aligned was not.

When the timing was checked the notch on the flywheel was not used but instead the dots on the right side. It is much harder to use the dots on the right due to the angle of the eye and the large hole in the cover.

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It is not possible to install a cam 180° off in a single cylinder, 4 stroke, engine and have any effect on it's running. The only difficulty would be installing the cam tower due to the spring pressure of the valves.

The engine comes to TDC once every revolution. Whether it is on the compression stroke or exhaust stroke is another story. There is no such thing as two TDC's and a relation to a dot or mark other than the correct mark on the cam sprocket. TDC will always align the dots on the right side because TDC is TDC.

The two gears on the right side engine case (driven gear and balancer gear) are 1:1. The dots on those gears are to have the correct balancer alignment with respect to the counterweights of the crankshaft. They will align every revolution.

One part of your statement it itching at me though... How could the cam align correctly on the exhaust stroke and not the intake stroke.... Somehow I am thinking cam chain tension... Because, mechanically, a gear ratio of 2:1 is 2:1 no matter what!

It sounds like the cam tower was installed by forcing the bolts down because of spring tension against the lobes!

The chain was being pulled to one side and what looked to be aligned was not.

When the timing was checked the notch on the flywheel was not used but instead the dots on the right side. It is much harder to use the dots on the right due to the angle of the eye and the large hole in the cover.

Maybe he checked it the first time with the chain tensioner on and the second time with it off.

Edited by tea bag

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Dust Devil you shouldn't be so confident if your skills are limited.

Edited by tea bag

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