A mechanic looked at my motor

[la400ex]

There is a guy down the road from me that has been working on fourwheelers for a long time. I stopped by his house today and he followed me to my house to look at my motor. He pointed out some things that I didnt see. You can see on the top of my piston where the valves hit it. I didnt see that. The intake valves are bent. I didnt know that either. He thinks that my flange came lose and it got out of time. Then the valves hit the piston and snapped the rod. I cant think of anything else that would have made the rod snap like that. I was only running 10.8:1 compression and im sure it was lower than that with the head gasket. I think he knows what he is talking about. I know it was timed right because it ran perfect up until the rod broke. It started with no trouble at all and didnt kill. Anybody else agree with him? Thanks, Anthony

[VegasEx'r]

The valves hit the piston & made the rod snap? I guess anything is possible (especially when a rod is broken), but the rod is a lot stronger/beefier than the valves, so it seems unlikely. Of course, he has actually looked at the motor, & I am getting to play the role of "armchair mechanic", so I might put a little more weight in what he says.

Sorry to hear about your quad.

[MIKE400EX]

Take a look at the splined area on the cam & cam flange and see if there is any evidence of rotation. Were they aligned properly when you took the motor apart? I wouldn't think the cam and flange could slip, it would have to be noticeably loose when installed. Is there any possibility that the cam could have been installed off time, maybe you didn't notice a power loss but the valve to piston clearance was diminished? Did it get revved against the limiter alot (and the valves floated)? Many questions to look at. Good Luck!

[Mxbubs]

Anthony, I had the EXACT same thing happen to my motor. I know of one other guy that this happened to. Your motor jumped timed, but we need to figure out why?

Look real hard at the head. Look to see if the 2 bolts that hold the cam sprocket on the cam flange, rubbed the side of the head. This is what happened to me. I had a web cam. The other guy I know had a web cam. Its like the flange had a slight bit of play, about 5 thousandths. However, when revved out, I believe that 5 thousandths spun out to around 15 thousandths, causing the flange bolts to rub against the head, slowing the cam just briefly, causing the motor to jump time, making the valves collide with the piston, bending the valves, and breaking your crank rod. When I called Web about this, they said I had no idea what I was talking about. The told me all they do is take honda cam, harden it, regrind it, and press the flange back on. I suspect that in pressing the flange on, this created slack, and this slack hits about 1 in a 1000 customers they have in the form of a blown motor.

Or, your timing chain has just stretched over time, and jumped. Either way, you are looking at spending some money.

Been there, done that. (Good Luck)

P.S. How is the Hammond Track now?

[la400ex]

Mxbubs, I checked to see if the bolts rubbed against the head but I didnt see anything. My mom called hotcams about it. I didnt wanna even try so she did it. They want me to send them my whole motor. I will prolly just end up spending a lot of money for shipping and then not getting anything out of it. Thanks, Anthony

[roostu]

Are you sure the piston was installed correctly? I know a guy on this forum that un-knowingly installed his piston backwards and caused the piston to hit the valves. This did not cause an engine failure (seemed to run fine), he just happend to see it when he took his engine apart to install his new cam. It is possible that the same thing happend with your piston, and something else caused the crank failure. I don't have the answer but just food for thought.

~Roost-U

[Pappy]

i have heard of many engine failures caused by what the mechanic told you. not just in quads either....on a ton of import cars if the timing belt snaps it will do exactly as he described.

i would highly recommend sending the motor to hot cams? i would be interested in seeing what they will do for you. shipping isnt that bad or hard to do.....so i figure its definatley worth the effort

[la400ex]

What is the best way to ship something like that? I gotta get the motor out first. That swing arm pivot bolt aint budging. My dad is gonna pick up some blades for the reciprocating saw tomorrow. This guy knows a lot about engines. He figured that out quick. Hes got a warrior with a yz 426 in it. I cant figure out why he would put a motor like that in a warrior frame but its a nice bike. Hes tryin to sell it to me. I might stop buy his house and ride it one day. Thanks, Anthony

[speedjunkie]

Tlk to the frieght company and get exact guidlines for shipping something like that. I know ALL the oil has to be drained. I would just build a crate for it. Sound like the guess on what happened could be very true.

[Castor-426ex]

whatever happened had to be hard....cause rods arent soft

im interested too because im doing the 416/426 kit and im curious what to change or look over

[Mxbubs]

I have a yz 426 quad too dude....Maybe if im ever at holeshot mx we can ride together.

Go to Walmart and get a big rubber made storage box...put the motor in it, pack it with news paper, foam, etc....drill holes in the lip, and tie wrap the lid down...

Give me the number to hotcams, I will call them and tell them what I know....

Mxbubs

[JOEX]

Originally posted by VegasEx'r
The valves hit the piston & made the rod snap? I guess anything is possible (especially when a rod is broken), but the rod is a lot stronger/beefier than the valves, so it seems unlikely. Of course, he has actually looked at the motor, & I am getting to play the role of "armchair mechanic", so I might put a little more weight in what he says.

Sorry to hear about your quad.

"Arm Chair Mechanic" LOL! That's great! Just might have to borrow that one!:D

Joe

[YZROOSTINYA]

i am thinking that the rod snapped then hit the valves, not vice versa.

typically valves will bend before causing any damage to the lower end.


it takes alot to break a rod. i have seen valves completely destoyed and banged around it the head with no damage to the rod or lower bearings.
either way good luck

[Predator36]

Originally posted by YZROOSTINYA
i am thinking that the rod snapped then hit the valves, not vice versa.

typically valves will bend before causing any damage to the lower end.


it takes alot to break a rod. i have seen valves completely destoyed and banged around it the head with no damage to the rod or lower bearings.
either way good luck

I am with you on this one. I have seen 4 rods break and know a few freinds who have seen even more. The rod breaks - not from high compression but from fatigue of a week rod (the stock Honda rod is not built for the RPM that a lot of guys are running) that is accelerated when running at high rpm a lot. I saw one go with a stock piston. This is the reason for the heavy duty rods installed by most of the engine builders. It is the weight of the piston jerking on it at top dead center on the exhaust stroke and the violent front to back movement of the rod at high rpm that causes the failure of a weak rod.
I also agree that it is a good thing to send it to Hotcams for a good check out. They not only understand cams but can diagnose which came first the chicken or the egg as they also understand and design rods. Dont expect them to repair your engine for free but use their knowledge to help you choose parts that will give you the reliability that you desire.

[roostu]

Originally posted by Predator36
I am with you on this one. I have seen 4 rods break and know a few freinds who have seen even more. The rod breaks - not from high compression but from fatigue of a week rod (the stock Honda rod is not built for the RPM that a lot of guys are running) that is accelerated when running at high rpm a lot. I saw one go with a stock piston. This is the reason for the heavy duty rods installed by most of the engine builders. It is the weight of the piston jerking on it at top dead center on the exhaust stroke and the violent front to back movement of the rod at high rpm that causes the failure of a weak rod.
I also agree that it is a good thing to send it to Hotcams for a good check out. They not only understand cams but can diagnose which came first the chicken or the egg as they also understand and design rods. Dont expect them to repair your engine for free but use their knowledge to help you choose parts that will give you the reliability that you desire.

I agree with this. This is a common problem with 350X motors. In a 350X if you left the motor alone it was fine, as soon as you put in a high compression piston, or a rev box or another cam the stock connecting rod would break. Even if the motor was bored over just one size during an engine rebuild we ALWAYS replaced the connecting rod because the increased power and weight of a bigger piston would cause the rod to break.

~Roost-U