plug getting loose

[ericlachance]

Hi, my spark plug on my 96 yz250 seems to get loose after I ride it. I was thinking it might be due to detonation, but I never heard her ping. What do you guys think? I wanted to run it on race gas, but at 80$ canadian for 5 gallons (so about 110$ a day with the premix oil and tranny oil) It's a little expensive for me... Any other possibilities? quick fixes? I know octane boosters aren't worth crap, but can It help with a minor problem like mine?

thanks

Eric

 

[bclapham]

eric- thats more than likely detonation- sometimes you cant hear it, maybe time for a bigger main jet and/or move the clip 1 notch

 

[Moto Squid]

Are you crushing the crush washer on the plug when you tighten it??

 

[ericlachance]

I usually hand tighten the plug than turn it a little with a 13/16 wrench, but not much. crushing it would cause it to leak wouldn't it? anyways, thats what I allways thought.

I was pretty sure it was detonation. I usually dont open her up much though, I ride in the lower half of the power band cause It just plain scares the crap out of me. The pilot seems to be ok, only a very slight hesitation when opening it up wot from a stand still(I was too lazy to play with my air screw). I do have a little amount of spooge dripping from my silencer, but not much. I use 94 octane pump gas.

come to think about it, I did use mostly 1-2 to 3/4 throttle openings, so I will lower my clip by one position(would that be right?).

thanks for the help

Eric

 

[bclapham]

torque the spark plug down properly before you assume its coming loose from deto. you have to crush the washer- thats why its there

 

[ericlachance]

Don't get me wrong, i do torque it down, I hand tighten it, than turn it another (maybe 1) turn. The washer is crushed, but not completely. Should I crush It completely? what If I have to take the plug off though? Won't I have to change it if the washer is completely crushed?

 

[ericlachance]

even the guy I bought it from said he had to check the plug onnce in a while cause they got loose.

 

[Dirtykid]

this completely off topic, but where in Quebec do you ride ????

 

[ericlachance]

héy, salut! j'pensais que j'étais le seul québecois.

I live in longueuil so the closest track is the one in st-Julie, but I've never even riden on that one. i usually go to yamachiche(near three rivers). it takes about 1 and a half hours to get there. How about you? where do you ride? what bike do you have?

Eric

 

[David Trustrum]

Could well be the thread is a bit boogered. A plug should never come loose. Might be time to helicoil it.

 

[ericlachance]

Thanks David I'll take a look at that, anyways, I might have another ride or to left before I take her apart. She syill reads 210psi of compression with a cold engine, but I'll take the engine apart anyways to check tolerences and to take the carbon deposits off my powervalve. I'll check the condition of the threads at the same time, and if I have to, install a time-sert or helicoil at the same time.

 

[cr25096er]

210 on a cold engine sounds high, try a hot engine! A cold engine usually reads lower than a hot one.

 

[bclapham]

whatever you do, i would torque the plug down to the manufactuers specs before putting a helicoil in there!

 

[ericlachance]

Yeah, I was supprised too when I saw the reading. I'll try it hot. But I'll try it with my compression tester this time(just bought it last week). Last time, I borrowed one from the mechanic where I work. It hadn't been stored great so I think the reading might be a bit off. Especially considering the hours I have on it. (Last owner had about 40 easy hours on it and I got about 20 very very very easy hours on it.)(that's still over 60 hours though so comp should be around 175 maybe).

Eric

 

[darringer]

The 210 compression reading is not too high. My CR regularly runs between 210-220psi. Compression checks are not the best wear indicator on a top end. I freshened mine up last winter and the compression was still 200+. By my measurements on the piston, ring, and cylinder, it was time.

 

[bigred455]

Originally posted by darringer
The 210 compression reading is not too high. My CR regularly runs between 210-220psi. Compression checks are not the best wear indicator on a top end. I freshened mine up last winter and the compression was still 200+. By my measurements on the piston, ring, and cylinder, it was time.

.........

I totally agree, that is not too high 03 kx 250 cold 212 hot 225. 50+hrs. Compression test is valid if you take it right after break in and check ever so often for the lbs to drop 10%

 

[ericlachance]

Anyways, Ill be taking it apart pretty soon, to clean my powervalve(I find it easier if the engine is not on the bike) so I'll check piston and bore dimensions as well as ring gap.

Does anyone know what the wear limit is or where to find that info? I have a wiseco piston and a shop mannual, but I was thinking the dimensions listed in my shop mannual only applied to oem pistons. Where could I get this info?

 

[ericlachance]

bclapham, i really appreciate your info and help. for some reason, I trust you... You strike me as the kind of person who really knows what they are talking about. also, you were nice to me with my race gas questions... I'll try what you said. i'll torque it down more. Only problem is I can't fit my torque wrench between the plug and the gas tank unless I take the tank off, wich is not very practical... So I'll torque it down with my 13/16 wrench like I usually do. How much do you reccomend I turn it?

I wasn't torqing it down much cause this is what my clymer mannual says:

...use a spark plug wrench and tighten an additional 1/4 to 1/2 turn after the gasket makes contact with the cylinder head.

NOTE: Do not overtighten. This may crush the gasket and cause a compression leak.

Thanks again
Eric

 

[Rich Rohrich]

Originally posted by ericlachance
I wasn't torqing it down much cause this is what my clymer mannual says:

...use a spark plug wrench and tighten an additional 1/4 to 1/2 turn after the gasket makes contact with the cylinder head.

NOTE: Do not overtighten. This may crush the gasket and cause a compression leak.

That advice from Clymer is essentially correct. Here's what NGK has to say about installation on their website (www.ngksparkplugs.com ) :

1. Installing spark plugs

Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind.

An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plug's inner gas seals or even cause a hairline fracture to the spark plug's insulator...in either case, heat transfer can again be slowed and the above mentioned conditions can occur.

The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult. Proper torque specs are listed below.

Spark plug Flat seat type (with gasket) 14 ø mm Aluminum Cylinder Head 18.0~21.6 (lb-ft.)

Here's the link to the excellent NGK spark plug basic tech info. http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=

The point is it's VERY EASY to over-torque a spark plug and destroy the threads in the cylinder head, or destroy the seal of the washer, so be careful about cranking it down too much.

It's worth setting your torque wrench to the spec listed above and tighten a few easy to reach bolts till you get a good feel for how that torque feels.

 

[darringer]

I think the measurements for the cylinder, piston, and ring end gap would be the same as OEM. Maybe the piston tolerances would be a little tighter.

 

[ericlachance]

hi Rich,

I don't even have to mention how much I respect what you say... Every one does! Anyways, I don't suppose you have a formula I could use to convert lb-ft to lb-inch ? I have a 3/8 drive torque wrench but it only has newton-meters and lb-inch on it. Not lb-ft. I'm thinking thats somewhere 175lb-inch but i wanted to make sure.

Thanks again for the info
Eric

 

[steve125]

12 inch lbs to 1 ft.lb.......so 20 ftlb's=240inch lbs :thumb:

 

[Jonny426]

lb/ft x 12= in./lb. I put a lot of plugs in aluminum heads on a weekly basis. A small dab of anti sieze on the threads will help keep them from galling/excessive wear, and a cool engine is the safest time to mess with plugs. I tighten plugs so I can feel the crush washer compress, just to the point where you feel it stop, or bottom. like Rich suggests, try torquing some easy bolts to see what 18-21 ft/lb feels like.

 

[ericlachance]

ok, It might be time to go to bed. 12 inches in one foot... Thats logical... Thanks guys.

Eric