Valve adjustment

[Westfield 11]

Originally Posted by Macaw

My old yamaha had them as did my '73 XJ12 not a biggie and does keep the valve clearances better than the other alternatives.

I can't imagine that it would keep the clearances better than hydraulic adjusters. IIRC the advantage of cup type adjusters over the shim and bucket type is that cups will not be able to spit the shim out at high RPMs since there is no shim. Other makers avoid this by putting the cheaper replaceable shim under the bucket. Be prepared for some sticker shock when you have to replace the cups with those of the correct size. It costs a lot more to make a precision ground cup than a dime sized shim.

[andywert]

Note to self: sell or trade in the smart at 58,000 miles
Imagine all the new features on the 2012 fortwo!

[jwight]

Originally Posted by andywert

Note to self: sell or trade in the smart at 58,000 miles
Imagine all the new features on the 2012 fortwo!

Good point! Apparently Porsche uses cup tappets on the 911 series so we're in good company (and probably similar replacement cost.)

[PeteInLongBeach]

Originally Posted by jwight

Good point! Apparently Porsche uses cup tappets on the 911 series so we're in good company (and probably similar replacement cost.)

Right. There is absolutely NOTHING unusual about the valves, seats, followers, etc. on the smart. It is a very conventional motor. Just be happy they designed it with a timing chain instead of a timing belt. One less significant maintenance item to deal with.

[Fredvon4]

4 valve head
3 cylinder motor = 12 "buckets"
intake cam is hydraulically manipulated to adapt timing and power output
chain driven overhead cams
tight motor bay
@ 60,000 valve lash must be measured ??? = "x" shop hours
if clearance is out of specification then motor must be lowered to gain access to cam drive chain cover
Both cams removed
each valve "bucket" that is out of spec replaced
Buckets will be $15 ~$45 each x 12 (I would never just replace some and not all)
Shop hours will be around 6 to 8 for this service

no data is available to let us know if 60,000 is too soon, just right, or too late

Fair to assume that Mitsubishi recommends 60,000 because that is where their test motors starting showing wear that required replacement "buckets"

I am hoping to find source for these parts and do my own top end work and NOT pay nearly 100 bucks and hour for this....or get rich before both my smarts hit 60K....grin

the though of trading before 60K is my fall back position

[PeteInLongBeach]

I have a hard time believing that there is no means of adjustment in the cam followers. There are 2 kinds of valve gap issues:

• Too much gap due to cam and/or follower wear, resulting in relatively benign tapping noise and less valve actuation
• Too little gap due to valve face and valve seat wear/recession resulting in valves that do not close completely, losing cylinder compression, and eventually burning the valve.

The latter is the one I'd really be concerned about, and I haven't heard of a 4-stroke piston engine that does not have some means of valve gap adjustment (adjustment screws, shims, etc.). New "cups" (followers, lifters) would not address valve recession. What would they do, grind down the cups to restore valve gap? Something is missing from this story....

[Fredvon4]

Pete nothing is missing

The procedure is well documented for the 4B series motor that this 3B variant is related to.

There is no "adjustment"... so to speak... replacing the "cups" with corrected sizes is the only method

They have a large variety of valve lash adjustment "cups" designed to bring the clearance back into spec

I have to go back and research, but if memory serves, the replacement "cups" were all PLUS sized. This indicates the wear is from the cam lobe and the "cup" face increasing the clearance too much

In other words it seems that valve stem stretch, or valve face recession are not the normal wear mode and they are not concerned with too close a clearance causing burned valves

I disagree with your first bullet conclusion... this is a high rev motor and 4 valve head with low density parts availability and ZERO aftermarket motor parts

As the gap increases the results are not "relatively benign tapping noise and less valve actuation " as you suggest.

The more the gap the faster the gap widens.... or more wear per unit of time/RPM...

Who knows how much wear becomes too much, and catastrophic damage occurs because the micro millimeter cam lobe hardened surface is compromised

[kannonvaggon]

This method of using shims to adjust the valve lash is very common on motorcycle engines and works just fine. My understanding is that the metal used for the shim is slightly softer than that of the cam lobe and stems... so most wear is on the part easily replaced.

Good top end lubrication with clean synthetic oil should allow those shims to last quite nicely.

I have an engine in my sidecar rig that has adjuster bolts on solid rockers and pushrods. It needed to be tweaked for lash adjustment every few thousand kilometers until it got broken in smoothly at a bit over 50 thou. Now that engine has over 250 thou on it and almost never needs a tweak of the valve adjusters. The good news is that this sort of valve system costs NOTHING to adjust yourself and can be done with a couple wrenches by an idiot in a few minutes. There is sumthin to be said for SIMPLE sometimes ....

;-)

[fortow]

Originally Posted by kannonvaggon

This method of using shims to adjust the valve lash is very common on motorcycle engines and works just fine. My understanding is that the metal used for the shim is slightly softer than that of the cam lobe and stems... so most wear is on the part easily replaced.

Good top end lubrication with clean synthetic oil should allow those shims to last quite nicely.

Apparently the smart engine does not use shims. The cups are replaced instead.

Nontheless, the wear on this type of valve train is mainly in the valve head seating. The tolerances tend to tighten, not loosen as a result. So, if people are expecting to hear tapping sound to alert them to do an adjustment, they may never hear that. The clearances should be checked periodically, at least at 60,000 miles to make certain that there is still some clearance left. Otherwise burned valves may have to be replaced.

[Mike T]

My ~250,000 mile Peugeot 405 DL uses cups+shims and the valve clearances have not needed anything to be checked or replaced/done in 20 years....and that distance.