[faintreality]

Anyone know what the stock compression should be on an 08 CRF450R?

I purchased used and it's so much easier to kick than my 08 CRF250R, so I figured I would check the compression and see if I'm good or have issues.

Also, any tips or guides on how to go about using a leak down test?

Thanks in advance,
Dave

[faintreality]

So it looks like the 08 has a compression of 78psi. When testing mine, I was sitting at 65psi after warming up the engine, approximately 15% drop.

I also did a leak down test which was around 20%, yet I could hear no air leaks or bubbling when at TDC. I did hear air escaping where the leak down tester was plugged into the spark plug hole...

So now how do I go about narrowing down the cause of the low compression?

[JimDirt]

Is there a O-Ring on the Leak Down tester plug ?? , it needs a O-Ring on the treads to make a complete seal , same goes for the Compression Tester , as that will give false readings

Have you checked valve lash to make sure the Intakes have not tightened up ?? , as that will give blow by also , but usually you will hear it coming thru the carb

[mossman77]

So it looks like the 08 has a compression of 78psi. When testing mine, I was sitting at 65psi after warming up the engine, approximately 15% drop.

Compression should increase after the engine is warmed up, not decrease. I think you'd better do your tests again, this time making sure you aren't getting leakage by the tool's plug fitting.

[faintreality]

Is there a O-Ring on the Leak Down tester plug ?? , it needs a O-Ring on the treads to make a complete seal , same goes for the Compression Tester , as that will give false readings

Have you checked valve lash to make sure the Intakes have not tightened up ?? , as that will give blow by also , but usually you will hear it coming thru the carb

Both the compression tester and leak down tester have the o-ring on them. Maybe the o-ring is bad?

I am going to check the valve clearances this weekend as well as check the compression again after putting a little oil in the plug hole. My buddy says if compression goes up after doing this, it's the top end.

[faintreality]

So it looks like the 08 has a compression of 78psi. When testing mine, I was sitting at 65psi after warming up the engine, approximately 15% drop.

Compression should increase after the engine is warmed up, not decrease. I think you'd better do your tests again, this time making sure you aren't getting leakage by the tool's plug fitting.

I got around 58psi cold and 65psi when warmed up. According to the service manual, 78psi is ideal.

[JimDirt]

If the valves check out within spec , then it sounds like the rings are going , so basically time for a Piston , do you know the history of the bike ?? , like when the last , if any , piston replacement was done ?? , when the valves were replaced or adjusted , if ever ?? , as it still could be a valve issue or a combo of both valves and piston needing replacement

[jonbuchli]

I don't think you can get a good reading with an auto decompression system. My mechanic says it's difficult to do a leak down test too. When I tested my car it gave a reading of 160 lbs and on my Honda it only registered 75.

[mossman77]

I don't think you can get a good reading with an auto decompression system.

Sure you can. The auto decompression isn't engaged when at TDC of the compression stroke. You should have no problem getting the proper numbers if you perform the leakdown and compression tests properly. Be sure the tool itself is not leaking at the fitting/spark plug hole!

[jonbuchli]

I was referring to the standard method, where you insert the compression tester and kick the bike over. Also, from what I've heard, it's a challenge to hold the engine at TDC while pressurizing the combustion chamber, as the pressure forces the piston down.

[JimDirt]

To hold the engine in place all you need to do is put the tranny in gear and either rest the tire on the ground so it cant spin , or if the engine is on the bench by chance , then you can put a channel lock on the countershaft sprocket and hold the engine from turning that way , OR you can use the Counter Balancer gear on the right side of the engine , behind the large round plug , with a socket on it , so there are several ways to keep the engine from turning past TDC when doing a leakdown test

[jonbuchli]

That is correct, JD, I only attempted the standard test, and I will go out and buy a leak down tester and try it. Also, since you seem knowledgeable, my 07CRF450R became hard to kick start hot or cold, but bump starts easily. Also now it won't hold idle and can backfire sometimes when kick starting. Cleaned carb, rejetted, new fuel adjust screw, checked for air leaks. Intake valves are a bit tight at .07mm. Could that cause these symptoms? Thanks!

[JimDirt]

Yes it would definitely be the issue , you will need to replace the valves

The recommended settings for your bike would be
INTAKE: 0.006 in.(+/-0.001 in.) / 0.16mm (+/- 0.03mm)
EXHAUST: 0.011 in. (+/- 0.001 in.) / 0.28mm (+/- 0.03mm)

So your intakes are way too tight , you can maybe adjust them a few times before replacement , but you will only get a few rides before it moves again , which means they are at the end of their life span

You can either replace them with the stock (or aftermarket) Titanium intakes if you are racing , but if you just ride to have fun on the track , or just trail ride , or are not worried about the weight difference of the Titanium Intakes , then you can go to Stainless Steel Intakes and save yourself a ton of maintenance , since the Stainless will last several times longer before needing adjustment (i have gone 7 years without needing a adjustment on my 450X and just switched to Stainless on my 450R this past winter)

You will usually have to replace the springs with the Stainless since the weight difference requires stiffer springs to avoid valve float

General replacement (usually requires replacement of springs, and retainers as they are considered wear parts , but going to Stainless (or Titanium) you are better off getting a matched set , where the springs are matched with the valve weight

Again , if not seriously racing , i would go the Stainless route , depending on the shops in your area you might want to consider sending your stuff to Ken here (i am in no way affiliated with CRF's Only , but i do trust his work and his prices are very competitive and better than most shops) , but he can either send you a complete ready to go head in your choice of stock to full race porting and machining , or he can redo yours , from mild to wild depending on your budget or specific needs , or as mentioned you can support your local shop , but be warned that a "automotive" shop might not have a clue how to do valve jobs on these 4 strokes (some do , but most do not) , they are not the same as a car head no matter what they tell you , nor do they use the same tools as the automotive heads do , so the shop must be experienced in working on these heads or just say Thank You , and walk out the door

So check around and find someone that is highly recommended for doing 4 Stroke Heads , not just car heads , this will make or literally break your engine if its done incorrectly , when a valve cuts loose because the head was not done right , it takes out everything , head , rod , piston , crank , and possibly cases , so be warned... do your research before sending your head , or leaving your bike at a shop for machine work ...

Here is Ken's head work and prices:

http://www.crfsonly.com/catalog/index.php/cPath/258

[jonbuchli]

Thanks much for the info, I had this problem on my 05 and put in stainless steel ProX valves/springs/retainers and they lasted hundreds of hours. It seems to be different this time, as if it has something to do with the carb, but I will go ahead and do the valves anyway. On my 05, the local motorcycle mechanic put them in and also put in a slightly higher compression piston (I ride at between 4000 and 10,000 ft elevation) and ported and polished the head. Even though I don't race, it was a total blast to ride! The higher compression seems to help out the power band, and didn't seem to affect longevity, as I usually ride in the low to mid range of the power band.
One more question on jetting, I have consistently gotten black spark plugs following the manuals guidelines on jetting, and have finally decided to go to a 158 main and 38 pilot, riding usually at 6000 ft. and 70 degrees. The power is much stronger and cleaner, and the plug color is normal. Could the manual be off in it's recommendations? And how much oil do you put in the engine and trans? I have been putting in .7 liters. Or do you go by the window/seep hole? I will check out your referral on the valve work and may go with him. Cheers, Jon

[JimDirt]

This is the basic jetting guide to go by , you should pretty much use a #45 pilot in all situations/elevations

Jetting Guide for Main Jet:(pilot 45) CRF450R/X

Sea level....165
2000 ft.......162
4000 ft.......160
6000 ft.......158
8000 ft.......155


Temperature/Elevation:
One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.

I would also check your Hot Start , to make sure its not stuck , though this usually creates a lean condition , it would account for some popping , etc , but it would not account for a black plug

The black plug would indicate to me a main jet too large and/or a over oiled air filter , all you want is enough oil to trap dirt , if you over oil the filter , it cant get air past the oil so it will run rich , this is a common issue with people worried about getting dirt past the filter so they oil the crap out of it and create a completely different issue , you did not mention what your Fuel Screw is set at , as this will indicate how your jetting is , also if you are trail riding a lot where you are idling and running low RPM's , it will also make the plug darker

As does the altitude , the air is thinner up there so it takes more power to give the same engine output as it would at a lower altitude , you will also put out less overall power even if jetted properly for the elevation , this is where the higher compression piston comes in , it will give back the bottom/mid punch you would normally lack with a stock piston

Your main jet is about right , but your pilot is way lean and this will cause some of the issues your experiencing as well as make tuning all but impossible , you need to get a #45 and then try to re-tune , i will bet you will like the way it runs , more than you do now , a leaner pilot will not help where the air is thin , your just starving the bottom end of the power

Your Pilot and Fuel Screw runs the first 1/4 or so of throttle , everything after that is controlled by the Main Jet and the Needle position , i would see what clip position your needle is set to , it should be either 3rd or 4th from the top , if its 2nd from the top this will lean you out even more

As far as oil , i put 1 full quart in the tranny , and don't worry about the level of it , just run a quart and your done , it won't hurt anything and is what most of us run in our 450R's and X's , in the engine side run to the top mark on the window , which should be equivalent to about 3/4 of a quart , and you should be good .....