exhaust packing woes

[Backslayer]

alright I can't seem to figure out why my bike keeps blowing out all the exhaust packing, This is the third time Ive repacked it in a few months, I use a wash plug, so its not water. what else could cause it to blow out like that, yes its installed correctly done quite a few, but i don't know the deal with this one. been using the moose kit with the wire mesh and all so what could be the problem? :bang:

 

[bwood]

Are you repacking a stock muffler? If not go with a kit from the manuf of the muffler. If so you might try a different brand packing. I have not used the Moose stuff. I used FMF 4 stroke packing.

 

[whenfoxforks-ruled]

FMF 4 stroke packing is fine for any muffler. Is the moose product specifically for 4 strokes? 2 stroke packing is different.

 

[oldguy]

We had a similar problem where Spider was blowing the packing out of his bike in about 2 hours of riding. DrD sent us a heavier packng that really helped but later we found the root cause was the bike being jetted to lean and burning it out to quick

 

[whenfoxforks-ruled]

You would either see the flames, or smell the packing burning. Try a 190 main in the 450, 4 footers, no lie!

 

[Backslayer]

alright thanx guys its stock. Its just weird, before i repacked it it was good but wasn't sure of the condition and decided to repack it and looks like i would have been better off leaving it alone and its the 4 stoke repack kit. have to look at jetting since its getting colder.

 

[whenfoxforks-ruled]

When is the last time you checked your valves? Its getting colder out, time to fatten her up? Maybe its the moose product?

 

[Backslayer]

could be I don't know fox. Checked valves exactly 11.3 hours ago, going to check them tomarrow. planning on doing a top end soon. Fox whats a good compression ratio to buy without having to switch to race gas.

 

[mideastrider]

wiseco 13.5:1 part#4852MO7800 works good on pump 93.

 

[whenfoxforks-ruled]

Pretty sure you can run the 13.5 on pump fuel. When you do the top end, check the thrust washer clearance on the big end of the rod with a feeler gauge. My sons 250f stock was big on the leak jet and pilot. The ap mod from ready racing eliminates a lot of hesitation, same as the o ring or wire mod. I sure wish he would have had it long enough to get the head work done from Eric, and a 14.6! But the 15 hour ring thing blew that, well, and the crank going out! The way he rode it, and the 14.6, I am sure we would have been looking at 5 maybe 8 hours on the rings. He did the valves same as Joe, recut, and lap stock ones. What kind of valves are you running?

 

[_JOE_]

Go with the 13.5:1 Wiseco. Nice boost in grunt on pump fuel. If you haven't done the ap actautor mod/leak jet tuning/squirt timing, there's a bunch of throttle response to be gained there. Just to clarify, you CANNOT lap the intake valves, it will ruin the coating. The exhaust valves are steel and can be lapped a bit as long as the face and seat are still in good shape. I have yet to actually swat the parts, I'm still waiting for them to tighten up again. Check the carb for dirt when you do the top end. Take the top cover off the carb.

 

[whenfoxforks-ruled]

Non-lap-able valves? There is no grinder or machine that can cut 2 separate items and get a dead solid seal?

 

[_JOE_]

There is a thin coating from the factory that maintains the integrity of the valve. The degredation of the coating is what usually cuases the valves to recess. That's why it's SO important to keep dirt OUT. One little piece of sand breaks the coating down and BAM, that valve's headin south. I've heard most people say the right intake tightens first, which I think has something to do with the carb giving dirt a direct path to the cylinder head. Supposedly the factory exhaust valves are steel and can be lapped. They tend to last a long time, maybe because the dirt gets incinerated during combustion or because it's being blown out?

 

[Rich Rohrich]

Supposedly the factory exhaust valves are steel and can be lapped.

The OEM exhaust valves on the CRF250 are made up of a Honda proprietary Inconel alloy (very tough stuff) head and lower valve stem which is friction welded to a more conventional steel upper stem (the portion that rides in the valve guide and above).

Once the Inconel valve face degrades it has to be ground (not lapped) to restore a proper seal. The reality is, it is almost always cheaper and a damn sight easier to buy a new valve than it is to find someone with the equipment and skill required to grind these valve faces properly.

 

[Backslayer]

Just checked my valves and the exhaust valves were out .003 in one question do i go to the tight side or the loose side when getting new shims. hey rich in my manual i know that you really know your stuff, but it states NOTICE, do not lap the intake valves. They are titanium and have a thin oxide coating, Lapping will damage this coating Fox as far as what's in the bike, I bought it used and have a recept that its got the kibblewhite ss in it. don't know for sure, planning on doing the whole top soon just want to get last few races of the series before I do though

 

[Rich Rohrich]

but it states NOTICE, do not lap the intake valves. They are titanium and have a thin oxide coating, Lapping will damage this coating

If you go back and read what I posted with the same care you read your manual you'll see I was talking about the exhaust valves. ;)

The manual is correct. When the intakes vales wear you throw them away. :cool:

 

[Backslayer]

Sorry about that thanks for clarifing. Should I go to the tight side or loose side.

 

[Rich Rohrich]

You should set it as close to the middle of the spec as you can get. Setting things loose will shorten the cams opening ramp and really hammer the valve train.

 

[Backslayer]

thanks for the information rich. lesson learned

 

[whenfoxforks-ruled]

Do not forget the thrustwasher clearance. Do they have a number on how much material is removed from lapping? It removes the coating? It has to be thick enough to grind or cut? Coated afterwards? Match a valve that has a track history of being out of round? Kibbles