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Post by trobie on May 25, 2007 15:47:10 GMT -5
I have just finished a top end rebuild on my SR.. Did the rebuild due to what I though was piston slap, and a .03 piston to cylinder clearance confirmed this ( I thought ). Replaced worn 11:1 compression piston and cylinder barrel. Did a squish test and put er back together. Bike runs strong, but still has the noise!! Loud valvish clank.  Checked and rechecked the valve clearance and cam chain tension. I think the bike has a megacycle cam, not sure which one, from the previous owner. I called them and they think I have valve to piston interference, but the earlier squish test said otherwise. I was thinking of using a piston stop to make sure the tdc mark on the rotor is correct. Any ideas of where to go from here? Any input is much appreciated. |
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uk500
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Post by uk500 on May 28, 2007 4:53:19 GMT -5
Hi, I can't help much with this but I noticed you said that the squish test has eliminated the possibility of valve to piston interference. A compression test will only prove that both valves are closing and seating properly and that your piston/rings/bore/head/gasket etc are in good condition and producing correct compression, it would not show if you have a slight interference, especially if it is a small enough contact not to cause damage, so based on a compression test alone interference would still be a possibility I reckon, Cheers, John,,,,,,,,,
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uk500
Junior Member
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Post by uk500 on May 28, 2007 5:06:48 GMT -5
Hi again, if it is a TINY bit of valve piston interference, you might get away with just grinding your valve seats in a little deeper then after re-adjustment of the clearances your valves would'nt extend so deeply into the combustion chamber :-) ,,,,, Cheers, John
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uk500
Junior Member
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Post by uk500 on May 28, 2007 5:29:10 GMT -5
Another thought,,,,,,AS A TEST (if it's just a Tiny interference) you could increase your valve clearances, this would make the engine run badly but the valves would'nt go in the chamber so deeply, so if the "clank clank" vanishes, you've determined the problem without stipping the engine first, it would probably be the exhaust valve wouldn't it? Or you could take your plug out and turn the Engine manually you should hear/feel a tiny "blip" at the collision point, at the very least your piston head and valve should show collision marks when you strip the engine,,,,Hope I'm right or I reckon I'll be in disgrace for a long time after writing this lot,,,,LOL,,,,,,Cheers,,,,,, John,,,,,,,,,,,,
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Post by motomick on May 28, 2007 6:50:50 GMT -5
how about setting tappet clearances at nil,to see if clank dissappears,(just start it,& a quick blip of the throttle,or fast idle??),sometimes with big cam lifts over time, the rockers tip can hammer a concave in the valve stem,feeler guages tend to miss that?,but usually a valve clatter,not a clank!!,hth?,cheers Mick
ps UK500 ,squish isn't comp test,it's piston to combustion chamber clearance at TDC,(using soft wire soldier usually)
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uk500
Junior Member
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Post by uk500 on May 28, 2007 16:15:21 GMT -5
Whoooops, Thanks for pointing that out mick, I thought that squish test was a bit of jargon for comp test,,oh well blown that one :-) but if he sets his tappet clearances to nil and there is an interference problem it could wreck the engine,,,,,anyway from now on I'm just gonna read threads and ask questions when I get stuck ,,,,feel a bit of a mug a the moment,,,Cheers, John
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Post by wotavidone on May 28, 2007 17:22:32 GMT -5
I'm gunna sound like a cracked record here, but here goes...........
By all means check all the stuff you are talking about, but my SR pings under load on premium fuel with a 10:1 piston.
With 11:1, I'm thinking you ought to try avgas and see if the clank goes away.
Mick
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Post by fenz on May 28, 2007 22:12:17 GMT -5
You say that the motor has a cam in it.I have heard of motors that are fitted with very strong valve springs can tend to make some strange top end noises as the valve snaps shut.
Just another theory to totally confuse you....
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Post by trobie on May 29, 2007 8:27:08 GMT -5
Thank you for all the responses.. I did a couple more things. Note: I have the thick copper head gasket on it. Must be an 1/8" thick. • Set the valve clearance to the correct one for the megacycle cam. • Emtied the tank and carb and refilled with 93 octane • Took a peek through the plug hole to see if I could see interference on the exhaust valve ( looked good ) • Read the plug after running it up to 4000rpm under load and killing the engine ( looked good as well ). Clanky clank. I'm going to hook up a timing light tonite and see it she's way off, but I suppose it wouldn't run well if it was. Could be the valve springs. I know the megacycle cams come with harder springs. Has anyone else noticed noise with them? Friggin confused.  |
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Post by colinjay on May 30, 2007 22:47:56 GMT -5
Hi all,
I just thought that I might stick my nose into this and confuse everyone even further.
Another possible causes of the noise could be the valve springs "coil binding" if they are being compressed to far by the megacycle cam. It is difficult to check as it is hard to see the valve springs with the head assembled. If you slowly turn the engine over with the tappet covers off and look in at the springs using something like a dentist mirror you may be able to see if there is any clearance between the coils of the springs when the cam is at full lift. Normally when setting up hot cams and HD springs there are some checks that should be done of spring fitted height etc.
In regards to the squish test. A "Squish" test of the piston to head clearance will show if there is sufficient "Squish band" clearance which is an important factor in having good combustion. If the squish clearance is insufficient, then when the engine has WARMED UP you may get the piston just lightly touching the head and an engine rattle / sounding as if it is about to self destruct. If the noise ocours as soon as the engine is started from cold, then there must be either no squish clearance or some other problem.
You can do a similar test to a squish test to determine the clearance between the valves and the piston during overlap phase of the cam timing, by placing strips of plastercine / modeling clay into the valve cut-outs on the piston and measuring the thickness of these strips after having turned the engine over at least 2 full revolutions. Normally you need a clearance of about 1mm to ensure that the valves do not touch the piston once the engine has warmed up.
Years ago, I had problems with the inlet valve touching the piston in one of my hot SR engines fitted with a Wiseco 11:1 piston and a WEB 88A cam, after the head had been plained to raise the compression to 14:1 to run on methanol. To stop the valve hitting the piston we put the piston in a milling machine and cut the valve pockets deeper into the crown. Which is a biggish job.
CJ
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Post by aero on May 31, 2007 10:42:48 GMT -5
Why not try some plastigauge, or plasticine on the valve springs to check if they are binding?
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Post by motomick on Jun 5, 2007 8:39:10 GMT -5
easy way to check for coil spring binding is tappett covers off,rotate motor via flywheel, watch for full lift,then with a flat largish screwdriver attempt to push the valve thurther down by gently leavering down on the rocker tip,soon tell you if anythings left to compress?also could let you know how far the piston to valve clearance is at that point,with a 1/8" thick copper headgasket i don't think you have a problem with squish clearance?,& i still think topends don't clank,they generally clatter  cheers |
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Post by trobie on Jun 5, 2007 9:01:38 GMT -5
Am finally gonna get back at it. Had to take a break to rebuild the carb, which all of a sudden was either overflowing gas out the overflow, or starving the engine. In response to colinjay and motomick.. Are you saying that if the spring compression is too much it is basically bottoming out, forcing the springs to compress past each other, or transferring the energy to the rocker arm and camshaft? I'm going to take a look at the valve springs during lift, and try pushing the valve down as well. Hope to find something out soon |
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Post by trobie on Jun 24, 2007 9:39:05 GMT -5
Ok,
Checked for coil bind, and double checked the valve to piston clearance using the screwdriver technique ( lever the valve / rocker down ), and I've got plenty of play left.
NOTE: When I rotate the motor by hand using the stator cover bolt, I hear a 'thunk' about once per turn. You can feel the thunk lightly through the wrench.
Could this 'thunk' be the higher pitched clank when the engine is running?
ALSO: I took the bike by a local mechanic for a quick look, and he said it sounded like the valve clearance was way out.
But it isn't.
Any idears?
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Post by StewRoss on Jun 25, 2007 2:27:35 GMT -5
Out of interest....remove the magneto cover and grab the rotor and see if you can move it up and down...checks your mag side main bearing... SR  |
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cheers 
