M/8 valve seat failure.
 

Has anyone doing upgrades on the m/8 encountered valve seat issues. Over on htt there is a thread and a link to a T-man video where he encourages people to do a leak down test. He has found a few heads (one with 700 miles)that had a loose seat. Now he does a leak down test on the bikes prior to tear down. He believes the the machining for the seats may be a little "sloppy" in a few cases. I believe this is something else to keep an eye out for. Especially if someone is going to the trouble of doing upgrades... I think I,ll do the leak down test on mine when I get a little better weather. Max

I respect T-Man and his knowledge but I also think he overreacts to stuff and is willing to charge people for new valve seats and so forth because he feels the leak down test is excessive.

I'm not saying HD is perfect but given the qty of bikes sold with zero problems gives me skepticism.

Could be valve seats or it could be that single rocker arm that actuates 2 valves each with no adjustment. One valve could be hanging open a bit while the other is fully seated. I said as much in the beginning when I saw the design. Time will tell; the exhaust seats will recede first because of the heat. It remains to be seen if the "adjusted for life" claim HD makes is true.

After seeing the pics, I'd check mine.

Definitely not going to check mine,or lose any sleep worrying about this pseudo leak down story.

What I see happening also. Doing dual valve seats and getting exactly the same depth and seat angle has to be fixtured and machine done there will be no free handing it and getting it right.

You're probably pseudo correct.

Did you make a claim at the Dealer? This would be an automatic head swop claim,no sweat.

I think changing what is "normal" is more cost effective than improving quality control or thorough r&d. You know... 20oz in the flywheel area, 5oz of fluid transfer every few tanks of fuel and 13% leak down in the cylinders.
This is the first harley I have had that I have not modified. (other than ac and exhaust which I can swap back). My bike has given me no problems thus far. But I have no confidence in it.......I would love to do a 117 or 120
build ( No harley parts) but that might be when things go South...And the dealer i have would probably kick me and my "Seudo warranty" to the curb..
Love the bike ...The moco,not so much....

Really - if your spending the money to "stage out" your bike? get the valve train done & done right!

As for the no problems statement - WOW, there are plenty of M8`s on the lift at 2 of the dealers I frequent, issues stated are: oil pump failure, ring seat failure, electrical corrosion issue (New Heritage), cracked heat shields & fastener issues......I could list more but its trivial QC stuff that should have been checked - then there is the faux parts that are 2 sided taped on falling off!

not going to bother if it aint broke why look for trouble

In the case of "uneven" valve function due to the single rocker design I would suspect that the fault mode would most likely be one valve with additional or excess lash relative to the other valve. This is because the hydraulic lifter will only pump up to the point of zero lash at the tighter of the two valves, leaving the remaining valve loose (additional lash).

I don't think the design would ever allow one valve to hang slightly open relative to the other. If that were the case Harley would be replacing burnt valves on a regular and ongoing basis.

In my opinion the single rocker design is sound.

You have 1 pushrod operating 2 valves. The valve protrusion between the 2 valves would have to be identical, and the part of the rocker arm that meets, the valves, would have to be identical in order for the valves to close identically. HD tolerances don't allow this, this is something that will need to be addressed in the aftermarket and on a case by case basis. Hand work will need to be done for perfect fitment.

Exactly, valve spring will keep pushing lifter plunger down, only after plunger bottoms out will one valve be held open. And I'm willing to bet you would be looking for a noise and/or driveability problem long before this happens.

If you watch TR's video you can see this issue has to do with valve seat fit in the head being too loose. Of the two bikes in his video one has excessive leakdown while the other doesen't. Difference being the one that showed leakdown had much higher miles.

I agree with you to the point of the stack-up of tolerances and multiple interfaces that play into the valve(s) function.

The point I was making is that the fault mode (when and if one exists) with this design is that one valve will be looser (more lash) than optimal rather than one valve being too tight and not completely seating.

So now, how significant is it if one valve is slightly looser than the companion valve? That's debatable. But certainly, it is not catastrophic as would be the case originally proposed (one valve not fully closing).

It's a new MoCo design, so naturally it's got design-defects and problems.

Nothing new here. The real surprise would have been if it DIDN'T have issues.

Just give 'em 8-10 years and they'll have it all straightened out (maybe), then they'll immediately abandon the design altogether and come up with something else "new & wonderful" with the requisite new set of defects and problems - guaranteed!

All you need to to is accommodated it in the set down ramp.. Make em longer.

What exactly do you mean? I don't understand. What ramp? Cam profile?

Cam profile.. You fix the difference in valve stem clearances in cam profile. Not too hard..

While T-man has seen issues with the seats, my bet is that it was a manufacturing glitch.. Locals (dealers) probably get groups of bikes off the assemble lines.. His area likely got a shipment that had batch of motors with bad heads..

Cam Profile...That's what I thought you were referring to.

But how does cam profile have anything to do with the discussion at hand, specifically with the concerns of operating two valves with a single rocker arm?

Makes zero sense to me.

Great, everyone's LS7 heads, and now this...

When the cam opens the and closes the valve, the opening and closing ramp will make a difference in how hard the valve get yanked off or hits the valve seat. Hot cams like the crane and woods cams drop the valve pretty hard on the seat.. Others are nice and easy. HD has very long set down ramps compared to the hotter cams. Makes em quiet.. Some HD owner feak out over valve reain noise. This is a picture of a stock TC and M8 cam. The brighter one is the M8. You can see that the M8 is a little slower. With a rocker arm ratio of 1.625 to 1 on both cams.. The ramp only needs too be 0.0031 higher(and it ends up being a little longer) at the end of duration to set both valves down on the seat at the same velocity if there is a difference of 0.005 in valve clearance.


https://cimg4.ibsrv.net/gimg/www.hdf...77ff06b12a.jpg


Hope this makes sense.

BTW, If the issue was simply how hard the valve hit the seat that was causing the issue, There would be a ton of TC heads with loose valve seats. Crane, Woods and possibly Leinweber would be the culprits.

Max,

Ok then. We're talking about two completely different things.

You're talking about shock loads imparted on the valve/valve seats based on cam profile.

The discussion I was involved in was in reference to a concern others had of one valve never fully seating because of the single rocker arm design.

The two are completely unrelated.

Thanks for the clarification.

Sorry I thought the valve not seating was already debunked. If not it should be..

Add:
What sets the lifter position will be the tightest valve..

I was wondering how long it would be before something like this came up with the 4-valve motors.

Even the Beemers provide for individually-adjustable valve clearances in their 4-valve twins by using variable thickness semi-spherical shims in the rocker tips. Did the MoCo actually believe that it could produce parts that were so accurate that they could bypass any kind of provision to match the clearances? Also, that all the individual parts would wear EXACTLY the same amount over time?

That's nuts - even for the MoCo - and that's sayin' a helluva LOT! Without being able to match the clearances, one valve will always open & close slightly before or after the other (depending on which one you're looking at), and that will cause a slight difference in the overall valve timing for each head as a result.

However, I can't really see how this could possibly cause any damage or excessive wear to the valve train components. All it does is affect performance.

So do the 4 valve beemers have hydraulic lifters?

No, but the lifters have nothing to do with whether the valves open and close together.

I don't see one valve slightly lagging behind the other as a problem. Max is right that tightest valve sets the lifter, if there is only .0005-.001 difference between both valves it wouldn't be noticeable.

I wonder what the specs are on this, how much difference would be too much?

I don't think its so much the valves "seating" or the seating process due to cam profile as it is a proper seat? which I spoke to a tech about such when they had one on the stand - seems that the particular bike having issues was due to valve seat irregularities.

This might be problematic going forward? who knows, hopefully this is just early model release issues due to vendor specs being off or no QC. it would be nice to have the number of bikes sold compared to the number of issues (warranty) work done to get an idea of percentages. This might help would be buyers? is it 1 of a 1000 or 1 of a 100?

Good luck getting those numbers, I doubt there's a motor company out there that would release them.

That's not entirely true, let one lifter fail & then see what happens - especially on the M8 valve train, if that was true then why not run solids? Hyds have a give & take factor basically & when not performing right will affect valve operation.

maybe for street riding you wouldn't mind that but in the performance field - what you mention is unacceptable - hell that's unacceptable for me for a street bike, should be no lag at all....!

Yeah I hear ya, and the truth is - its normal!!! isn't that what we are told until the normal becomes clearly abnormal. LOL

If you look the pics at the end of the video, it sort of looked like the seats were pressed in cocked also the shinny area also looks like machined surface was rough possibly due to a dull cutter or aluminum stuck on the end of the cutter. In that case, its a manufacturing issue and like occurred for a short run before the issue was realized and fixed. Hopefully this issue is not reoccurring.

BTW. Not all failure could be from bad machining.. What about a coolant system problem?? The passages only cool the exhaust valve area. If the cooling system fails to pump adequate oil/coolant through the head due to blockages / issues with pumps how does the rider tell? Excessive heat in that area could loosen the seat??

I wouldn't fret over it. Bablecookie has told the folks over at HTT that the video is "bogus".

Wouldn't the shinny area in the head be where the counter-bore and the seat were flush? Wouldn't the area that shows the carbon in the counter-bore be the problem?

Hmm, a third stab at it. Cam profiles, shock loads (not my words) and now a cooling malfunction. How about you just give the guy credit that has it in his hands. "This is going to create an issue down the road with the seats coming loose in the heads and it should be checked. The machining of the seat hole is off."

If/when the unequal wear becomes a problem, I'm sure the good ol' MoCo will determine that "it's normal, they all do that", and that, regardless of how much difference is building up between the valves, that it's "in spec".

Remember the Golden Rule - "He that has the Gold makes the Rules"!