[BigBird82]

Hello everyone. I am new to this forum and was wondering if anyone could help me. Here is the case:

2004 Predator 500. We were on the dunes and all of a sudden my buddy said it started to lose power then just quit, It was then very hard to get it to start after that. Once it did start, I heard a loud knock the engine was making. Not the normal ticking these engines make.

This goes to step 2. When we got it home we did an engine tear down and decided to do an engine refresher. We had the cylinder honed, installed a new piston, wrist pin, piston rings, intake seals, exhaust seals, intake valves, and shimmed the valves to spec in the OEM service manual. Got a compression reading of 100. Upon start up, we primed the oil pump. It started extremely easy. Next, we started to hear a ticking but no serious knocking. After letting it idle for a while, we got anxious and decided to take it for a quick spin. About 1 minute of riding it, it just quit and did not want to start again. Upon tear down we removed the head again....Uh oh... we made a dumb mistake. Somehow we managed to put 4 intake valves in the head and left the exhaust valves out. This explained why we had to shim very high on the exhaust side. The valves smashed into the piston quite a bit. The piston was cracked, exhaust side valves were bent. About the only thing that was good was the intake valves. There was no apparent damage to the head where the exhaust valves seated and somehow the cylinder was not scratched or gouged. It also appeared that timing was not in sync after this happened so we spent even more money all over again.

Step 3. Now total in the motor we have NEW:

Piston
Rings
Wrist Pin
Intake Valves
Exhaust Valves
Intake seals
Exhaust seals
Timing Chain
Timing Chain Tensioner

The valves are now shimmed to OEM specs again. Fresh oil and filter. I reused the head gasket since it was new during the first build. Timing marks are all on per the OEM service manual. Same as it was the first time that is started so easily. Here is the issue:

I am only getting a compression reading of 58. Now it is extremely hard to start. And when it does start, that loud knocking noise is back. Do not even want to keep the engine running when hearing it. That is how bad of a sound. We have done almost a completely new top end. Does anyone have any ideas as to what the noise could be and why compression is now so low? Help please.

 

[Bruce!]

Welcome to the board!:med:

 

[RVS Performance]

Did you rotate the rings so that all the gaps are spread out and not overlapping each other? I typically try to get them all about 1/3 of the circumference apart. 120 degrees. There are 3 gold marks on the timing chain that should line up with marks on the bottom gear and both cam gears.

58 is not enough compression to run. That's why it is so hard to start. The knocking is likely the valves hitting the piston again.

 

[BigBird82]

Did you rotate the rings so that all the gaps are spread out and not overlapping each other? I typically try to get them all about 1/3 of the circumference apart. 120 degrees. There are 3 gold marks on the timing chain that should line up with marks on the bottom gear and both cam gears.

58 is not enough compression to run. That's why it is so hard to start. The knocking is likely the valves hitting the piston again.

Yes, that is exactly how I spaced the rings out in the cylinder. Actually what was in the service manual as well. Yes, the three gold marks are lined up. The lower one at TDC mark and the cams are also on the dots. Exactly matching the descriptions in the service manual.

I tore the motor down again tonight. I noticed the exhaust valves were very lightly touching the piston. No serious damage though.

Another note to any with advice:

Before tear down tonight, I was spinning the engine with a wrench on the end of the flywheel to see if I could hear anything. Previously, I was able to move it freely through the compression stroke. Now I noticed that it would mechanically bind up when the exhaust lobe was almost allowing the valve to come almost all the way up. Then I could muscle through it and get about a revolution or two out of it, then it would bind up again. However, I decided to try to spin the engine backwards to see if the same problem was present, and it wasn't. Process of elimination began. I removed the magneto cover and intermediate gear between starter and flywheel. It still bounded up when turning with wrench. I the removed the clutch side cover and removed the clutch assembly. It still would bind up. I then decided to remove the cam chain. It did not bind up after that. So I take this issue is still in the valves and camshafts.I have scoured every forum and piece of service manual for info. I am 100% the timing marks are on and 100% I have shimmed the valves within specification.

Next step will be shimming the exhaust valves again to gain a little more clearance to ensure no touching. Hopefully there is no binding or knocking. I took it to the dealer when it was all tore down the first time and their service guru told me that the rod is okay and in tolerance. So I am assuming that is not rod knock. But that still raises the question, what gives with low compression? On some threads, guys have said that the auto release mechanism on the exhaust cam will often give inaccurate readings. Weird thing though is I had 100 PSI when I had the WRONG valves in the exhaust ports. Just for sake of argument I will be putting a new head gasket on it again as well.

I will be doing this this weekend. So if anyone has any tips or advice before the weekend, lay it out on the line. Please.

My toolbox is about do have a dent in it from my head. :banghead:

 

[RVS Performance]

My bet is you had the exhaust valves timed 90 degrees off. There are 2 dots on each cam gear and they go opposite ways. Intake are at 9 and 12 o'clock exhaust is at 12 and 3 o'clock with the gold links at the 12 positions.

 

[BigBird82]

Not to knock the advice being given but this thing is timed correctly. Same as the pictures and diagrams in the service manual. I also have the "rabbit ears" on the lobes as well when at TDC. Then I also had a DVD for reference and the individual in the video pointed that out as well. This how it is set up:

 

[RVS Performance]

That's right, both 9 and 12. Going off memory isn't always right.

 

[Talon]

Do the exhaust valves move freely in the valve guides with no springs, you may have damaged the valve seats when the valves hit the piston and went back into the guides.

 

[BigBird82]

It is running , no noises, and it just keeps on running as smooth and quiet as can be. I knew for some reason that the exhaust valves were still hitting the piston. The sprocket on the end of the camshaft was only pressed on there. So i figured maybe when the valves were hitting the first time, the sprocket could have turned a few degrees. Went on ebay and ordered a used exhaust cam. Bingo! The sprocket had turned and with the new exhaust cam in there, everything is good. No knocking and compression is up. It starts easy and keeps on going. You would think that a keyway in the camshaft for the sprocket would keep that issue from happening. However, I am not an engineer nor try to be one. It is fixed and running, so thats all that matters.

 

[RVS Performance]

Glad you got it. That's a tough thing to spot.

 

[baddad]

Good call what a pain, I was leaning valve guides. The engineer at HPD builds up and machines cams for the preddi 500 and he welds the cam gear in place.