Jump to content

04 crf450

Recommended Posts

Think i only got part of my question in im new to posting but my intake valve contacted the piston breaking stem of valve and punching hole in piston do i need to replace timing chain and tensioner did the t chain slip or could anything else have happened because all i can think of was the chain slipped causing the contact i ordered a piston and both intakes and intend on recutting valve seats and replacing piston do i need to buy a t chain and tensioner your help is greatly appreciated thanx

Share this post


Link to post
Share on other sites
1 hour ago, twostroke69 said:

Think i only got part of my inuestion in im new to posting bitt my intake valve contacted the piston breaking stem of valve and punching hole in piston do i need to replace timing chain and tensioner did the t chain slip or could anything else have happened because all i can think of was the chain slipped causing the contact i ordered a piston and both intakes and intend on recutting valve seats and replacing piston do i need to buy a t chain and tensioner your help is greatly appreciated thanx

I'd buy a new cam chain, manual cam chain tensioner and a new crank, piston, etc. Personally, I wouldn't trust the crank. I'd at least have It rebuilt (might as well put new crank bearings and seals In It too). Inspect the cylinder.

That's me though (picky).

Share this post


Link to post
Share on other sites

You seriously think a complete rebuild is required this is expensive there is no connecting rod play not sure why one would spend 500 on a new crank its the difference of 1500 to 2000 bucks thats crazy does anyone agree with me here or am i crazy

Share this post


Link to post
Share on other sites

But if the piston made contact with intake valve am i right in thinking the chain slipped for this yo happen or could it have happened because of anythimg else thanx

Share this post


Link to post
Share on other sites
1 hour ago, twostroke69 said:

But if the piston made contact with intake valve am i right in thinking the chain slipped for this yo happen or could it have happened because of anythimg else thanx

Timing chain tensioner failure most often is the problem but also if a valve retainer broke or anything that would allow the cotters to dis lodge. It would be very rare for an intake valve to just break in two but Im sure it has happened. Sometimes with so much carnage its hard to figure out what the root cause was. Sometimes it helps to know how the bike was being ridden at the time and how high the engine rpm was.  Its possible the cam can be damaged also, the upper timing gear hub can turn or slip out of position.

It sounded like you said just one of the intake valves dropped? Is the cylinder destroyed also?

Share this post


Link to post
Share on other sites

No the cylinder is fine the valve broke right at the stem and was upside down punched through the piston also the bike wasnt real hot i was trsil riding at the time and wasnt being hard on it was jst putting around really i pulled 3rd and it made a clattering noise and that was it i wish i would have checked the timing when i opened it up but it never crossed my mind but when you said aboit droping a valve that must be what it done due to a retainer is what stands out to me now would you agree thanx for your wisdom by the way

Share this post


Link to post
Share on other sites

So just one valve was broken and the other one untouched?

Anyway if it is a retainer or cotter issue you might be able to tell by looking assuming they werent lost or further damaged after the main failure happened.

Share this post


Link to post
Share on other sites

Ya jst one valve so anyway i installed new piston timing chain and both intake valves put her all back together timed it and all it does is back fire it will not start now jst bang every third kick er so om stumped xhecked the valves ovet and over checked the timing over and over jst about out of my mind with this thing

Share this post


Link to post
Share on other sites
12 hours ago, twostroke69 said:

Ya jst one valve so anyway i installed new piston timing chain and both intake valves put her all back together timed it and all it does is back fire it will not start now jst bang every third kick er so om stumped xhecked the valves ovet and over checked the timing over and over jst about out of my mind with this thing

Your cam chain timing is off

you should be using the 2nd index mark on the flywheel to time the motor, not the dot on the drive gear.

Edited by nesc103y

Share this post


Link to post
Share on other sites

I did use the flywheel marks and crank dot the last thing i can think of is posibly that maybe head gasket is the loss of compression the gasket was in good shape and wasnt leaking anti freeze at all a fella told me that sometimes you can reuse the gasket and im thinking that was a bad idea

Share this post


Link to post
Share on other sites

Yeah if the head gasket is leaking replace it but keep in mind the possibility of a turned upper cam gear hub, sometimes when valves get smacked by the piston (for whatever reason) it causes the cam, upper cam gear to get held up momentarily but the crank hasnt stopped yet. So if the cam gear hub gets turned out of position on the cam it causes incorrect valve timing even tho the marks can line up.

Edited by TDW

Share this post


Link to post
Share on other sites
23 hours ago, TDW said:

Yeah if the head gasket is leaking replace it but keep in mind the possibility of a turned upper cam gear hub, sometimes when valves get smacked by the piston (for whatever reason) it causes the cam, upper cam gear to get held up momentarily but the crank hasnt stopped yet. So if the cam gear hub gets turned out of position on the cam it causes incorrect valve timing even tho the marks can line up.

True of the newer bikes, but Aren't the older cam gears bolted in place?

I don't do much work on the older bikes so I don't remember.

 

Share this post


Link to post
Share on other sites

Yeah the older bikes like the 04 the OP is talking about has a pressed on hub that the upper cam gear bolts onto.

Share this post


Link to post
Share on other sites

Hey guys thanx for all your help ive since done the new gasket and the bike is now running awome one kick every time hot or cold its nice not having to kick my guts out to fet it runni g ive litterlly kicked holes in the bottom of my comp5 boots destroyed a brand new set of boots but thats another story lol

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×