CRF's Only Forums

Hey guys!

The bike refused to start after I wash it last weekend, the exhaust at the " bend " got "warm" so it ignite atleast i think..

It went great at the track all day (sunday), no problem at all, it was a bit grumpy to start on saturday (had been standing for a month), but it started second try sunday.
I was rideing a sand-track, but it rained day before so it was perfect! realy fun ride. there are gopro vids if anyone want to see!

I was going to change piston this fall cause it passed a long time since i bought it last year. (bought in store used) so figured it might as well be time for it..

Problem 1:
When I unscrew the top and checked the valves , I did not even enter 0.05 (?!) intake (0.15 and 0.10 is "bad" right?), but the exhaust was a perfect fit.
I'm 90% sure that I was in "Top dead center or whats its called" because I could "move"/wiggle and measure the exhaust port , the two lines was also in line with the ledge.

Problem 2: Removed the spark plug , or had problems removeing it until I noticed that the rubber thingy from the spark plug wrench ( catching the spark plug ) remained on the spark plug! probably it had not as good connection to the spark plug after I wash the bike (washed under the engine by laying it down)
This is fixed now tho.

Issue 3:
Come down to the cylinder , and now find that the cylinder and piston had some " scratches " see pictures.
Nothing i can feel with the nail or finger, its just visible.
The piston was better on the other side as you might see on the cylinder( minor scratches on the side)
do i need a new cylinder ?

Issue 4:
The first time I do this myself, want to learn really hard so i have the interest but not knowledge


My English isnt to good, so please be patient and kind to me!






Thanks!

http://www.crfsonly.com/forum/viewtopic.php?t=38779

has a link for some better feeler gauges, but your specs (also on that same page) should be:
CRF450R
In -> 0.16 +/- 0.03mm (0.006 +/- 0.001 in.)
Ex -> 0.28 +/- 0.03mm (0.011 +/- 0.001 in.)

If you are certain that they are out of spec then you will want a shop to inspect the head and determine what is needed. Although most valves that are out need to be replaced, some can be salvaged. Again, let a machine shop tell you what needs to be done.

Photos do not do cylinders justice. From the photos it looks like it can be deglazed, but it also looks like you have a lip at the top (bottom of the first photo) that may be more of a problem - but again, photos are tough. Send the cylinder with the head and have them check it. Sometimes they only need to be deglazed, sometimes recoated. When it is time to re-sleeve look at just getting a new one.

The flash is either making it hard to see the marks and coloring of the piston skirt or it is worn the groves off in the center. Based on hours alone and what looks like oil deposits above the rings, its toast.

What is on the cylinder stud on top left of the piston? is that oil deposits, fresh oil, or anti-freeze? Looks like cooked oil.

riddler9 wrote:http://www.crfsonly.com/forum/viewtopic.php?t=38779

has a link for some better feeler gauges, but your specs (also on that same page) should be:
CRF450R
In -> 0.16 +/- 0.03mm (0.006 +/- 0.001 in.)
Ex -> 0.28 +/- 0.03mm (0.011 +/- 0.001 in.)

If you are certain that they are out of spec then you will want a shop to inspect the head and determine what is needed. Although most valves that are out need to be replaced, some can be salvaged. Again, let a machine shop tell you what needs to be done.

Photos do not do cylinders justice. From the photos it looks like it can be deglazed, but it also looks like you have a lip at the top (bottom of the first photo) that may be more of a problem - but again, photos are tough. Send the cylinder with the head and have them check it. Sometimes they only need to be deglazed, sometimes recoated. When it is time to re-sleeve look at just getting a new one.

The flash is either making it hard to see the marks and coloring of the piston skirt or it is worn the groves off in the center. Based on hours alone and what looks like oil deposits above the rings, its toast.

What is on the cylinder stud on top left of the piston? is that oil deposits, fresh oil, or anti-freeze? Looks like cooked oil.

Thanks for reply!

I think the valves are totally worn out, im replacing them with OEM titan valves..
Do i need to fix the "seat"? My friend can fix it cheap on the Scania manufacturing factory..

I understand it might be hard just by looking on the pictures, i didnt know actually what i expected I will show the cylinder to a friend tomorrow and he probably know what to do.

Its not the flash, its actually worn that much.. so the "darker" parts are oil from crank?

And i think its oil.. I tryd smell on the oil (from the oil-stcik) and i could smell gasoline in the oil.. i know how my friends oil smelled on hes CRF250 -10 (witch had alot of gas in its oil).
Maybe the piston ring is really bad and sucking oil from the crank..

The seats will need to be cut. What experience does your friend have with off-road MC heads? The tolerances are insanely narrow - they are essentially 1 cylinder of an Indy car engine. From experience (learned the hard way), I would not have anyone work on the head that does not have a stellar reputation of working on CRF heads.

You were definitely pushing oil past the rings, but that is not what would cause burned oil to be stuck to the stud. From the looks of things, the engine severely overheated and/or did not see regular oil changes at some point.

as mentioned the valve seats need to be professionally cut. stay away from those who use hand tools or mills and sell 'hand lapping' as a good thing. look for someone using CNC equipment designed specifically for cutting valves. NEWEN is the premiere CNC valve seat cutting equipment used by all deep pocket race disciplines. this is the equipment we use to cut seats and performance profile them and blend the port bowl. you need to also check the guides for spec. neglecting these steps will significantly reduce valve longevity.

ken