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Discussion Starter · #1 ·
Okay, long story short, I have 150psi from a stone cold engine. With oil introduced I get 190psi. What would you recommend? read below for more info.



I rolled my 660 a few months back and jumped timing, bent a valve. So I replaced the valve (lapped all the valves with lapping compound), replaced the timing chain, and installed new gaskets. Adjusted all the valves, and now tried a compression test to check to make sure the valves are all closing properly. So without having the motor started in over 24hours I have the compression gauge hooked up, cranking it with full throttle and am getting 150psi, with the oil in the cylinder I get 190psi.

Am I doing something wrong? Or do I really need to get back down to the piston and start replacing rings, or worse, the piston or piston sleeve?

When I had the jug off to replace the lower o-ring, I looked at the cylinder wall and they looked okay, there were no gouges and the rings fit tight in the cylinder when putting it back in, so I didn't think there was any problem there otherwise I would have replaced it while I had it apart.

I know the compression should be more like 180psi, So what would you do in this situation?

Thanks for any advice in advance
 

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Personally if it doesn't smoke I'd run it. It'll run with 80lbs of compression.
 

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The oil is just sealing the rings. It would probably cause the compression to go up on a bran new engine. I would run it for a while and re check it.

You also cant really get a 100% accurate compression reading with out bypassing the automaitc decompression setup. Other wise your bleading off compression.

Als you should be doing the compression test on a hot engine. That way the engine cranks over faster (no cold oil), and the rings are hot and fully sealing.
 

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Discussion Starter · #4 ·
Okay, I've read about both of those possibilities, the decomp spring on the cam and I've also heard to run the engine before the comp test which I didn't do. So how are you supposed to do a comp test on these if the decomp keeps you from obtaining an accurate reading?
 

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What you're measuring with the decomp in place is plenty... You can never get a true measurement with decomp in place because the amount of decomp is a function of the length of the decomp pin, which changes with wear and with temperature - so, be happy, your's is plenty good.
 

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Discussion Starter · #6 ·
Yea that's what I was wondering, but didn't know any better. So now my question is, now that I have it back together and started, it pops almost sounding like possibly a valve hitting and then the motor will die immediately after that pop, but of you keep it revved around 2500, the pop just makes the motor want to die, but it doesn't. You can also hear it miss a couple times if you accelerate the throttle, it backfires occasionally and I can see flames out the exhaust if I rev up it to about 60% throttle (kinda like slapping the throttle up to 60%)

What do you think would cause this? I know it's timed properly, and the valves are in spec. So I'm thinking maybe the spark plugs, the carbs, or the fuel is bad? The fuel was put into it just before the accident back in November. Would it have already gone bad?
 

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Yea that's what I was wondering, but didn't know any better. So now my question is, now that I have it back together and started, it pops almost sounding like possibly a valve hitting and then the motor will die immediately after that pop, but of you keep it revved around 2500, the pop just makes the motor want to die, but it doesn't. You can also hear it miss a couple times if you accelerate the throttle, it backfires occasionally and I can see flames out the exhaust if I rev up it to about 60% throttle (kinda like slapping the throttle up to 60%)

What do you think would cause this? I know it's timed properly, and the valves are in spec. So I'm thinking maybe the spark plugs, the carbs, or the fuel is bad? The fuel was put into it just before the accident back in November. Would it have already gone bad?
You may have the cam timing off................
Fuel shelf life is 30 days...........
 

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Discussion Starter · #8 ·
Well, I know the fuel is from back in November :-/ so that could be a possibility.

I replaced the spark plug because I know that I dropped it on concrete from about a 1ft high stand thinking it might have messed something up with that. So it now runs, still wont idle because as soon as it makes that noise it clicks and will die. At one time though it idled for about 15 seconds before it clicked and died? I cant seem to find where the clicking noise is coming from though, whether its the exhaust or the carbs. Its also missing if I rev it slowly, and backfires if I rev it fast. I want it running right before I even move it out of the garage.

When I went through and reassembled the head, I lined everything up as far as timing goes, but I guess that checking it again wouldn't hurt. But is there a way to check it without pulling the valve cover off again?

I've also never adjusted valves before, but I went through them and they all fit the feeler gauge that they are supposed to fit, so if they are off it couldn't be by much. How far off would they have to be in order to cause an issue like this?
 

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Master of the Electron
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Are you running with the air box lid off and what is your jetting? Sounds like you could be a little lean (if it's not a timing issue).
 

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Discussion Starter · #10 ·
Well for right now, since the bike is apart, I don't even have the airbox in the bike. As for jetting, I have no idea, the guy before me went in and put new rings in it before I bought it, he may or may not have messed with the jetting.
 

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It must have the full and complete intake system (snorkel, airbox, filter, etc.) that you plan on using, installed when setting the jetting or you will be extremely lean while testing, and then extremely rich when everythings installed. This explains your backfiring and flames.
 

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Discussion Starter · #12 ·
Okay, well I will have to put that together. Last night the water hoses coming out of the water pump into the block blew out. So I have that on order, but really can't do anything until I get that new hose in. Dealer says it will be late this week or early next week that it will be in :-/

In the meantime, I guess it's just a waiting game.
 

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Okay, well I will have to put that together. Last night the water hoses coming out of the water pump into the block blew out. So I have that on order, but really can't do anything until I get that new hose in. Dealer says it will be late this week or early next week that it will be in :-/

In the meantime, I guess it's just a waiting game.
Why did the hose blow, is there a headgasket problem............
 

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Discussion Starter · #14 ·
Well, I wouldn't guess that there is a head gasket issue. I just replace it when I rebuilt the top end. My guess is that the hose was just worn out, maybe I pinched it or damaged it when I took the water pump off, it looks to be the original hose, how often do those hoses wear out? What kind of head gasket issue would you think could cause a hose to blow out?

It is a year 2003 bike, so maybe the hose was just old?
 

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Well, I wouldn't guess that there is a head gasket issue. I just replace it when I rebuilt the top end. My guess is that the hose was just worn out, maybe I pinched it or damaged it when I took the water pump off, it looks to be the original hose, how often do those hoses wear out? What kind of head gasket issue would you think could cause a hose to blow out?

It is a year 2003 bike, so maybe the hose was just old?
A leaking head gasket can pressurize the cooling system and blow out aweak spot in the system.............
 

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Discussion Starter · #16 ·
Okay, I can see that. But no, I don't think there is a head gasket issue. Its a brand new gasket, and I added a bead of the gasket dealer to it as well. I'm just thinking i probably damaged it when I had it removed.
 

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Okay, I can see that. But no, I don't think there is a head gasket issue. Its a brand new gasket, and I added a bead of the gasket dealer to it as well. I'm just thinking i probably damaged it when I had it removed.
Adding gasket sealer isnt really a good idea on a head gasket since they were designed to be installed dry...........
 

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Discussion Starter · #18 ·
But if I had a bad head gasket wouldn't I be losing compression? I left it overnight on a compression gauge with 150lbs pressure and after 12 hours, there was still 150lbs of pressure. I can check it, but if I pull the head, manual says to replace the gasket anyway, that's why I replaced it in the first place and this new gasket has about 5 minutes total of runtime (testing for valve clearance and adjustments) on it since I put the motor back together.

Given that it holds that kind of compression, would you say to pull it and replace it again?
 

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But if I had a bad head gasket wouldn't I be losing compression? I left it overnight on a compression gauge with 150lbs pressure and after 12 hours, there was still 150lbs of pressure. I can check it, but if I pull the head, manual says to replace the gasket anyway, that's why I replaced it in the first place and this new gasket has about 5 minutes total of runtime (testing for valve clearance and adjustments) on it since I put the motor back together.

Given that it holds that kind of compression, would you say to pull it and replace it again?
Compression guages have a oneway valve in the hose or adapter that holds the highest compression you recorded for you to see should you not be able to watch the guage when checking for compression, there is no way an internal compression engine will hold that kind of compression for more then a few seconds................
 

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Good catch, Willy!

Sexton - just the gaps between the ring ends will allow the compression to bleed down in less than a second. Luckily, with the engine running at RPM, there is only a very small fraction of a second between compression and combustion.

Regardless, your compression, as measured, is fine... the symptoms you have described so far can be attributed to testing without full airbox in place... what's the problem? You don't seem to have any, in my opinion! You sure as hell don't have any reason to expect a blown head gasket - yet. Wait until you've got things back together fully before you start worrying about symptoms that aren't there yet.
 
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