bmxboy809
New member
I have got what sounds like a rattle comming from the motor on my 2000 SXR 700. With AEN tripple pipes this thing is loud and I can only hear the rattle while on the throttle and not at idle.
I have not yet had time to dig into it but last year I only rode it once, the trails were rough and It started running rough after 20 miles. It was getting dark and we just needed to get home so we kept going. After a while the rattle started. when I got home, I saw that two of the plug wires had jumped off? So this explained the roughness. I snapped them back on, it fired right up. Still has pleanty of power but the rattle still exists.
The previous year this sled ran great. I bought it from a sponsored racer and it has tons of aftermarket parts, always had all the proper maintenance done, and i got a good deal on it, so its worth spending a little money on.
I have heard that riding for a long ways with plugs disconnected and the fuel blowing by the rings can wreck the ring gaps. I have not done a compression check yet, and thats where I will start. Right before I bought it, it had a topend rebuild and i think a new cylinder head as well as a different head shim. Any ideas?
I have not yet had time to dig into it but last year I only rode it once, the trails were rough and It started running rough after 20 miles. It was getting dark and we just needed to get home so we kept going. After a while the rattle started. when I got home, I saw that two of the plug wires had jumped off? So this explained the roughness. I snapped them back on, it fired right up. Still has pleanty of power but the rattle still exists.
The previous year this sled ran great. I bought it from a sponsored racer and it has tons of aftermarket parts, always had all the proper maintenance done, and i got a good deal on it, so its worth spending a little money on.
I have heard that riding for a long ways with plugs disconnected and the fuel blowing by the rings can wreck the ring gaps. I have not done a compression check yet, and thats where I will start. Right before I bought it, it had a topend rebuild and i think a new cylinder head as well as a different head shim. Any ideas?
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rx1jim
New member
I would not worry damage to the rings. How could the fuel mixture damage the rings?? The lubrication oil for the engine is carried by the gas. On a 4 stroke engine if the jetting is very rich and is not ignited in the cylinder due to a bad spark plug or other ignition problem it is possible for the gas to get past the rings and "wash" the oil from the cylinder causing accelerated wear of the rings and cylinder. A compression test is a fairly coarse test to determine the condition of the rings, piston and cylinder. A leak down test is the best way to gauge the condition of the engine. It measures the percentage of leakage past the rings while the piston is stationary.
As for the source of the rattle, it could come from a few areas: excessive piston to cylinder clearance resulting in the piston(s) rocking in the cylinder(s) and slapping against the cylinder, worn connecting rod bearings or from worn parts in the primary clutch. You definitely need to find the source of the rattle. If it is due to worn internal engine parts, you need to fix it now since it will result is a serious failure doing damage to many engine parts.
Can you find out if the person who rebuilt the top end used new or the old pistons and if the piston to cylinder clearance was measured?
As for the source of the rattle, it could come from a few areas: excessive piston to cylinder clearance resulting in the piston(s) rocking in the cylinder(s) and slapping against the cylinder, worn connecting rod bearings or from worn parts in the primary clutch. You definitely need to find the source of the rattle. If it is due to worn internal engine parts, you need to fix it now since it will result is a serious failure doing damage to many engine parts.
Can you find out if the person who rebuilt the top end used new or the old pistons and if the piston to cylinder clearance was measured?
FJViper
New member
If your 100% sure it's the motor, that's one thing. Otherwise if it were mine I'd be checking everything. Motor mounts good? (ie:none broken?), chaincase internals good? (chain tension correct?), check the jackshaft for noise. Like Jim said, clutch? Grab everything you can and try to move it to see if it's loose.
Strange you can only hear the rattle when your on the throttle. In my experience any kind of piston slap/lower rod/bearing noise is pretty prominent at any rpm . Put the sled on a stand, have a buddy throttle it up slowly, get a dowel or mechanics stethiscope and start exploring.
Strange you can only hear the rattle when your on the throttle. In my experience any kind of piston slap/lower rod/bearing noise is pretty prominent at any rpm . Put the sled on a stand, have a buddy throttle it up slowly, get a dowel or mechanics stethiscope and start exploring.
bmxboy809
New member
Well I took it over to a buddies house, who is actually the original owner, and we pulled the primary clutch off and ran it. He said it sounded to him like it is a crank bearing. From the sounds of it, this sounds like a common problem with these motors for the crank to fail. What am I getting into as far as cost of parts to rebuild it?
Devilin AblueDress!
New member
Depends on which bearing. All bearings are relatively inexpensive to buy. Outter bearings cheap/easy to swap out. Inner bearing require crank to be pulled apart, installed pressed back together, can get pricey quick! If its one of the inners unless you have another buddy with a crank shop you might want to check on a rebuilt/reman crank and send yours in as core. Gasket kit and a tube of yamabond definately cheap enough to tear it apart for a look see. You ran engine with primary off?
bmxboy809
New member
Yes, Bill wanted to run it without any noise from the primary or drive train. This is the second motor for this sled and the original motor had a replacement crank already. Worst case it will be an inner main bearing, or i guess it could be a rod bearing, but either way it means a replacement crank. I am trying to figure out if its worth the investment in this sled thats pretty beat all around. its got aaen roller secondary, aaen primary, boost bottle, cleated track and AAEN tripple pipes, maybe it would be worth more to part it out.
I've never heard anybody say that having a bad crank is common to the SX redhead motor. Did you check the recoil and area under it?
Devilin AblueDress!
New member
Its one of those things to ponder. From the experience I have had with the red heads they are very dependable. My buddy has an 01 similary set up as yours. Season before last his started not turning the RPMs it usuaaly did. By the end of the season WOT was something like 75-7600. We tore motor down in the off season and PTO outter crank bearing had ALOT of slop in it. NEVER rattled, clanged, banged...Just was gradually loosing top end/RPM. Replaced bearing and ran like a champ all last season. You can tear it down now and check it out.....OR RIDE IT TILL IT PUKES!.......and prepare for the worst case scenario.