Did the bottom end go bad?

[JTrider]

I took my quad out for a ride this past weekend and I noticed a weird noise coming from the motor. It was like the valves were out of adjustment or like the cam chain was loose. I readjusted the valves and it didn't make a difference. Once the motor heated up the noise went away so I decided to take it for a ride. As I took off everything was good and then all of a sudden the noice came back and then went super loud and the quad quit. It sounded like I broke a timing chain. I just took the valve cover off and the chain is still good and everything else is good. I took off the clutch cover to look inside and everything in there looked good too.

The next thing I did was turn the bolt on the shifter side to find TDC and when I turned it, it felt like there was no compression. Does this mean the bottom end/rod broke? Does anyone have any idea of what could have happened or what I should do next?

Thanks,

[killer454]

do a compression test on it first.i would pull the valve cover and check to make sure the cam did not slip time first,check your cam gear marks for alinment on the head.if compression tests very little compression and timeing marks look good pull the head and cylinder and find the problem.

im new to 4-strokes but this is what i would do

[rubbersdown]

Dont know how mechanically able/knowledgeable you are but if you really suspect that you threw a rod bearing or something it is best to just tear it apart and not do a compression test because if something messed up in the top end or your rod bent you could do way more damage to the top end by continually turning it over to do a compression test. If there is any major mechanical failure as you suspect just tear it down and find the problem.

[killer454]

yes i agree with rubbersdown,i did not think about turning the engine over if a rod or piston come apart or bent.it would do more damage to the engine.
i do agree with rubbersdown and sorry for the wrong info,im really glad he posted on this.i will admit when im wrong and this is a time when im wrong sorry.

[CJM]

Is the timing chain tight? If not your tensioner is bad (little part onthe outside that bolts to the cyl) friends quad did the same thing sounded odd then just quit and when trying to start it up it had no compression.

In his case the tensioner was bad and failed another time cause the timing chain was stretched.

[JTrider]

Hey guys thanks for the info. I will guess I will be tearing everything apart and I hopefully its it not too bad inside. However, I have a bad feeling its the rod. I will update later this week when I get a chance to get a look. Thanks again.

[JTrider]

CJM, the cam chain was a little loose. I could pull the chain up to almost the top of the sprocket teeth. I will check the auto tensioner before the break down. Thanks

[CJM]

Originally posted by JTrider
CJM, the cam chain was a little loose. I could pull the chain up to almost the top of the sprocket teeth. I will check the auto tensioner before the break down. Thanks

That tells me the chain is loose, it should be tight period.

I would look at the two chain guides and the tensioner before doing anything else. You will probably find out its the chain.

[JTrider]

Your right about the chain. I looked at it tonight the cam chain has moved on the sprocket. It looks like it moved 4+ teeth. I know I need to replace the chain and probably the guides but do you think anything else could have been damaged? Valves, piston? I took pictures of the cam sprocket and chain before the problem and after. The T marks on the flywheel are in the same position in the window for both pics. You can see how the first pic everything lines up and on the second its way off.

[JTrider]

cam pic 1 with timing set

[JTrider]

cam chain after problem

[CJM]

It jumped time. Probably just a bad chain or auto-tensioner. But its best to change out all the related parts.

You need:
CRF450 timing chain (00-02 iirc)
Cam chain auto-tensioner and gasket
Guides
Rightside cover gasket

Its easy to change the one guide, just pull the head iirc, the other one you will have to take off the side cover, the clutch cable, the clutch itself and some
sprockets.

Its actually rather easy, most time spent was trying to get off the old gasket (pain), then remove the clutch. There is a nut you must unstake and you will need a clutch holding tool (rocky mtn has one for like 15 bucks or you can stuff rags all around the clutch basket and see if it works). YOu need like a 1 5/8 socket (I cant recall the exact size I used) and an impact gun works wonders to get it off.

Remove the clutch and basket and then you can get the chain, sprockets and chain guide off.

Its all described in the service manual, which if you dont already have either buy or download.

[rubbersdown]

be sure to look closely at your valves. Jumping time 4 teeth could have easily bent a valve if it hit the piston.

[CJM]

Originally posted by rubbersdown
be sure to look closely at your valves. Jumping time 4 teeth could have easily bent a valve if it hit the piston.

This is correct, I would seriously get a valve spring compressor and see what they look like all disassembled.

On the plus side you can regrind them too if you want using an electric drill and some grinding compound

[JTrider]

Is there a way to check valves without removing the head? Just asking since I just replaced the head gasket. However, if its safer to just remove it and inspect it that way I will do that.

Also, the sprockets seem to be in good condition, do these need replaced as well with the new chain.

[CJM]

Not really, you need to see the shafts of the valves in order to see if they are bent. A new headgasket is also recommend imho just incase. Sorry you just did it.

Sprockets are probably fine, look for wearon the theeth and worn spots. Im sure its minimal if anything.

[hocman123]

the gaskets are metal and can be reused. I used one 3 times and only replaced it because i got one for free with a new part i bought

[JTrider]

Well it looks the intake valves are bent but everything else looks good. You can see in the picture how the side is raised and not seated. The piston and exhaust valves are ok. Do I need to just replace the valves or do I need anything else?

[CJM]

Probably just the valves, inspect the springs too just incase.

[JTrider]

What do I look for in the springs? Should I see if they buckled to the side? Also, when replacing the valves should I replace the valve stem?
Sorry for all the questions but I have never dealt with valves before. Do you think I need to do anything with the valve seating area or how do you tell if I need to?

Thanks again

[rubbersdown]

The valve and valve stem are 1 piece. Do you mean the valve stem guide or seals? Def. replace the valve stem seals no matter what. as far as the guides, if they havent ever been changed I would change those to as they are not to expensive. When it comes to the valve seats allot of guys will get the new valve, put a little bit of chem dye or rubbing compound on the lip of the valve and the stick it in the head and spin it a little in its seats, if the valve touches all the way around (you can tell by the chem dye or rubbing compound will have transferred to the seat) you are good to go. it there are spots it doesnt touch, you need to regrind the seats.

[killer400ex]

yeah its called lapping your valves, you can buy kits in auto hardware stores, they usually come with a rod with a suction cup at the end of it and lapping grease or something, but you just apply the lapping compound to the face of the valves and the valve seats and install the valve back into its guide and place the suction cup on the bottom of the valve so it sticks to it and twist the rod back and forth between your hands like the image link shows

http://t1.gstatic.com/images?q=tbn:ANd9GcTgd6v__29nPzPMaGkybXA39AlJDrVOL dFRl-sEi1Ek1efY8PM&t=1&usg=__UXoLLWRJUiV4zFo-zJzJYdHgWfM=