Head Torque

[C George]

I'm looking for the Head bolt torque specs for a 1993 KDX-200 E model.

These ran a higher compression and just curious as to the factory spec.

Thanks

[Gotanubike]

18 ft-lbs

[C George]

Thanks ,,, So I guess 18lbs should hold a 180 psi engine.

[Gotanubike]

18lbs just feels so not tight that It's not even safe. I'd guess mine are somewhere around 23-25ft-lbs but I go by feel

[C George]

18lbs just feels so not tight that It's not even safe. I'd guess mine are somewhere around 23-25ft-lbs but I go by feel

I hear ya there Mine are 25 plus but then I was told I'd warp the head ???
If it's torqued evenly , how can that happen ?

[newbbewb]

because aluminum is somewhat flexible, the studs are small, the gasket is thin and kawasaki says so. I'm with you on the 18 ftlbs being wimpy, yet I've never had a problem in three engines following the manual. I doubt 23-25 ft lbs is going to hurt anything.

[Gotanubike]

My brothers Honda crf250 head bolts are 29lbs from the Honda manual and they are only 57psi @ 800rpm(kickstarting on dead cold). He was with me the first time doing a reassembly on the kdx motor(mainly because he owns the torque wrench) and he didn't think 18lbs was tight enough either...

For a motor that does twice as many revolutions...I'd have to check but I don't even think they recommend retorqueing the KDX head nuts after the 1st or 2nd ride....torque them down good the first time. More compression, less worry and hassle

[C George]

My brothers Honda crf250 head bolts are 29lbs from the Honda manual and they are only 57psi @ 800rpm(kickstarting on dead cold). He was with me the first time doing a reassembly on the kdx motor(mainly because he owns the torque wrench) and he didn't think 18lbs was tight enough either...

For a motor that does twice as many revolutions...I'd have to check but I don't even think they recommend retorqueing the KDX head nuts after the 1st or 2nd ride....torque them down good the first time. More compression, less worry and hassle

The modern 4 stroke like the CRF250 " R or X " is a copy of an Indy Car engine . Very short stroke " probably why the low compression " and extremely high rpm's ,, 12-13,000 !
They rate them at a high compression ratio like 13:1 but that can't be compared to what they'll show on a gauge.

Sorry , rambling here ----

Has any body ever found a significant difference in different aftermarket head gaskets vs. oem ? I believe the oem ones are coated with a clear sealant.
Moose , Cometic , Wiseco , ect ?? Whats you thoughts ?

[fuzzy]

100psi, or 200psi compression, neither are going to blow a head off tightened 'lil past snug' with grade 8+ fine thread hardware. The low TQ setting is likely do to the nature of aluminum on aluminum with a small gasket. Small Block Chevy head TQ is 60ft/lbs. What's kind of alarming is the 20ft/lb spark plug setting!

I hear ya there Mine are 25 plus but then I was told I'd warp the head ???
If it's torqued evenly , how can that happen ?

Would agree, even is the most important.

[Mario]

A couple things to add I have learned as a prof. mechanic.
Cylinder head and base nuts should be torqued after initial heat cycle and again after first ride. I personally check them every ride as part of my inspection/cleaning.
If you want to get super technical they should be torqued and re-torqued only when the motor is dead cold. Differences in the expansion coefficient of aluminum and steel will affect final clamping force. Torquing the fasteners while engine is hot will cause over tightening. Also I am sure the book does not specify this but the listed torque spec is used when stud/nut is installed dry, with no anti-sieze or assembly lube or locktight. If you apply lube then the torque spec will be different to achieve the same clamping force. This is strictly followed when assembling performance engines, all torque values specify assembly lube or oil on installation. Not critical when talking KDX head torque but something to keep in mind.
A note about using torque wrenches, by nature a torque wrench is the most accurate when used in the middle of its torque range. So using a 20-200 lb-ft wrench for a 25 lb-ft bolt is not a good idea and will likely give uneven torque between bolts.
Even torque is more critical then the final spec, and tightening the head in a 3 step process evenly will ensure good seal and no warpage.
I always use copper spray on a steel gaskets to prevent small leaks.
In my experience a loose cylinder base or head nut will cause the bolt to fatigue break upon tightening. I always replace the studs if they are old or rusted or if the bike was ridden with loose fasteners.
A pet peeve of mine is using a wire wheel to clean rust off of bolts and studs. By doing this you have now removed the rust and the protective coating on the fastener. Now it will rust even quicker. Get new hardware.

Here is an NGK Bulletin about torque and anti-sieze
http://www.ngksparkplugs.com/pdf/TB-063 ... isieze.pdf

[capnbluetootharr]

18 ft lb on a 8 mm head bolt .equals about 150 kg of force on the head . X by 8 studs and you have 1200 kg holding the head on . You are dreaming if you think going over the torque spec is going to help in any way.