Jump to content
Sign in to follow this  

About valves and coatings....

Recommended Posts

Its been on my mind - we know that motorcycle valves are generally coated - and lapping etc will take of that layer and essentially make them worthless apparently.

Whats the deal with car valves then - similar compression, temperature, rpm (ok so lower rpm but not much compared to a drz) - these are usually steel/stainless steel with no coating - just hardened. How do these live 100,000kms and how is it that they can be lapped into the valve seats will no apparent ill effects?

Share this post


Link to post
Share on other sites

they see no where near the valve velocitys a motorcycle motor sees.

if a drz or similiar only revved to 5,000 rpms there would be no issue.

Share this post


Link to post
Share on other sites

The only similarities is that they are internal combustion engines.

No family auto will ever come near the abuse. How can you say RPM's are close? What does your family car normally run on the hiway? 2500 RPM? Probably less..

Drop it into 2nd and see how long it will last..

Share this post


Link to post
Share on other sites

the new car valves are just like motorcycle valves from the factory

like the new EVO and WRX turboed high powered cars

as far as I know the newest GM v8's ( with in the last 4 years ) have coated valves

Share this post


Link to post
Share on other sites
The only similarities is that they are internal combustion engines.

No family auto will ever come near the abuse. How can you say RPM's are close? What does your family car normally run on the hiway? 2500 RPM? Probably less..

Drop it into 2nd and see how long it will last..

My prelude runs up to 7.5k.....vtec kicks in at 5.5k. Mine is a moderate revving car. I don't ride my DRZ harder than that usually (not up to 10k usually). Temps and compression are comparable also.

I reconditioned the head recently - the valves only needed a minor lap. Perhaps higher revving car engines come with coated valves as standard...

Doesn't surprise me that the evo etc have coated valves - I'd sure want them in an engine with that kind of muscle.

Share this post


Link to post
Share on other sites

do you have a tach on your drz?

at high way speeds the typical drz is is 7,000-8,000 rpm. big difference than just having a 7500 red line.

Share this post


Link to post
Share on other sites
do you have a tach on your drz?

at high way speeds the typical dr zis is 7,000-8,000 rpm. big difference than just having a 7500 red line.

Yup... what he said.

The best example of this is in the boat world. They take an engine right out of a car, and put it in an application where they spin at 70% or higher all the time. So... take that favorite little 2.5L Iron Duke GM engine, and put it in a car. It will run for 15 years and see 150,000 miles before needing any real work. (at 60 MPH that's 2500 hours) Put it in a boat... and it may only last a few years. (400 hours or so)

Also... car valves have a much bigger stem than the little 5mm units on our DRZ's.

Share this post


Link to post
Share on other sites

So its pretty much purely an rpm issue - so in a Harley or the like coated valves are probably not an absolute necessity. Clearly valve wear does not vary linearly with rpm, it must be a nonlinear relationship to cause these issues.

No tach on my bike, but it doesn't see any highways and very little cruising. Just hard starts and stops - Just town and twisties. :banana:

Share this post


Link to post
Share on other sites

non issue on harleys.

i think if you had a tach on your drz youd be suprised at the rpm it sees.

the coating is about longevity on a high rpm motor.

you can put non coated valve in it and it will run.possibly for many miles.but at some point it will have issues.

if you were building a pure race motor that the moving motor parts were treated as disposable? no problem with the lack of coating. the valve will be changed regularly as a anti fatigue failure measure.

Share this post


Link to post
Share on other sites

i think if you had a tach on your drz youd be suprised at the rpm it sees.

I sure was! I knew I'd see high RPM on occasion, but didn't expect to see 7000 rpm so often while cruising, nor did I expect to feel like I was lugging the bike at 4000 rpm!

Share this post


Link to post
Share on other sites

I like the Dr's comparison..Same motor, different applications and a whole lot less useful life.

Share this post


Link to post
Share on other sites

Rate of erosion from dirt particles on metal is approximately proportional to their velocity cubed.

So valve erosion at 7500 rpm vs 5000 rpm is (7500/5000) x (7500/5000) x (7500/5000) = 3.4 times as bad.

(assuming valve size is proportional to cylinder displacement)

Share this post


Link to post
Share on other sites

Hmmm, well with only one cylinder firing as opposed to a sequence of four or 5 or 6 cylinders it would be easy to underestimate the current rpm of the drz

Share this post


Link to post
Share on other sites
Rate of erosion from dirt particles on metal is approximately proportional to their velocity cubed.

So valve erosion at 7500 rpm vs 5000 rpm is (7500/5000) x (7500/5000) x (7500/5000) = 3.4 times as bad.

(assuming valve size is proportional to cylinder displacement)

Cubed eh? Makes sense - a squared term due to the kinetic energy of the particles and then velocity multipled in a again for the linear relationship between air flow and particles/second.

But are we saying that high rpm wear is largely due to fine abrasion/wear by hard particulates? What about just basic deformation due to heat and pressure on the seat? A hard layer would protect against that somewhat also...

Share this post


Link to post
Share on other sites

I would guess the wear is from both abrasive particles and from contact with the valve seat. The relative amount of each type would depend on how many particles get through the filter.

Share this post


Link to post
Share on other sites
Cubed eh? Makes sense - a squared term due to the kinetic energy of the particles and then velocity multipled in a again for the linear relationship between air flow and particles/second.

But are we saying that high rpm wear is largely due to fine abrasion/wear by hard particulates? What about just basic deformation due to heat and pressure on the seat? A hard layer would protect against that somewhat also...

Damn this is getting deep:D

Any thoughts on which oil could prevent this thing from getting to the 4th power?

Share this post


Link to post
Share on other sites

The motor oil should never be anywhere near the valve seats.

Share this post


Link to post
Share on other sites

Im just in the process of putting 4 1 piece wisco stainless steel valve in a 400 e ive had them in my 436 s model for 20000 miles with no issues. :banana:

Share this post


Link to post
Share on other sites
Im just in the process of putting 4 1 piece wisco stainless steel valve in a 400 e ive had them in my 436 s model for 20000 miles with no issues. :banana:

20,000 miles? the wisco are coated though eh?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×