Whine in a Mk10

[Tanks A Lot]

The whistle/whine is almost guaranteed to be caused by the spring and piston. I'm leaving the distinct whistle of older flow through pistons without a concave seat aside.

Fiddling with either, e.g. turning the spring end to end or rotating the piston, oftentimes cures the problem. I had stubborn ones, where this did nothing, just like in your scenario. I believe it is due to the combination of spring and piston, with special consideration towards the mass of the two. That may be why slightly polishing the spring ends did the trick.

What has done the trick without fail for me was leaving the system pressurized without any air flowing for a few hours. It's a trick I picked up from an ancient Sherwood manual and even though I was skeptic at first, it worked without a fail so far. I'm waiting for the day when this does fail me...

 

[Bloody Knuckles]

Well, @halocline , you're absolutely right: red herring.
Had two old Mk10's in the shop last week and  both whined at 3000 psi, but only one had a tiny squeak at 1500.
Traded the orange washer for 10x2 - no change
Rotated the main spring 1/2 turn. Changed seats and added shims. I started by trying to keep track of each step I took. But nothing worked. It was so frustrating by the end that I can't honestly say what did it for both regs.

It was clear that getting the IP I wanted was part of the harmonic issue. They both started over spec at 148 & 153.

I  think that flipping the spring over helped. I think that polishing the spring ends helped. And I think that settling for a slightly higher (138) IP than I had planned helped.

But it wasn't my magical o-ring.
Thanks for the skepticism, Matt. How it is I've never seen it before and now three in a row is telling me something. Maybe it's the switch from thick silicone in the old days to slippery T-71.

Well Rob, I'm glad I'm not alone in regards to your frustrations...I had the same discussion with "Halo" last spring in a DM exchange. To a tee, I experienced the same symptoms and same frustrations with two of my MK10's. I swapped springs end for end and reg to reg. Swapped pistons, replaced the seats with variable heights, installed all new O-rings many times over with varying durometers, utilized shims on one end, both ends and no ends. Micro-Meshed the hell out of all the components in contact with each other. Regardless the end result was the same, a varying degree of whistle at supply pressures above 2,000 PSI. Not sure what the magic bullet was, but eventually some combination or luck of the draw helped reduce the whistle. Problem solved? IDK? I hung e'm up and broke out the MK5's. But this much I can tell you. All I use is silicone so I don't think the "slippery T-71" is the culprit. On a side note, one of the options we discussed was SPEC utilization and Halo indicated he had good luck mitigating the whistle when packed with Tribolube. Possible fix...IDK? But alas, we come full circle back to the mythical SPEC boot dilemma and utilization on a MK10...Have you cracked that thing open yet???

 

[rsingler]

But alas, we come full circle back to the mythical SPEC boot dilemma and utilization on a MK10...Have you cracked that thing open yet???

Haha! I keep meaning to...
Too many things going on. But I will, and I'll share all the pics.

 

[halocline]

It is true that my packed MK10s have never had any noise issues. There’s no way for the spring (or the piston) to vibrate freely when deadened by the grease.

What has worked for me in stopping the whine is a combination of making sure there is a plastic shim on both ends of the spring, plenty of lubrication (excessive, really) on the HP o-ring, and maybe keeping the IP fairly low. I only say that because I generally don’t have any whining issues and I generally set IP on my balanced piston 1sts between 125-130 PSI with a reasonably full tank. That gives me plenty of performance and lots of room for the seat to wear and IP to inevitably go up a bit. I try to get several years out of a MK15 seat, especially, because I only have a few left and they’re getting harder to find and expensive.

 

[kdlv]

Yea... another whistling MK10.

Tried reversing the spring, replaced the shim with the spring alignment washer, which resulted in increased IP of 130-135 psi. Slightly higher than the 125 that I typically adjust to. No IP creep.
I even tested with a shim on top of the TIB where the spring makes contact. Not sure if one should be there. According to diagrams, there should not be one. But it didn't get rid of the whistle.
Well lubricated piston ring (with MCG-111, not with silicone grease). Piston wall is clean and in perfect condition. Also well lubricated with MCG-111 there. No excessive lubrication though.

Tried a rubber ring instead of the red HP seat o-ring.
I even left it pressurized for 4 hours at 130 bar, as I read above in the thread that a bit of time under pressure decreases the whistle. It did indeed decrease a bit. Id doesn't whistle below 100 bar.

What's next in your experience? Should I remove all the unnecessary parts: the spring alignment washer and extra shims, decrease IP to 125, clean the MCG-111 from the piston and piston ring and try with ordinary silicone grease?
And would it be ok to keep the piston wall lubed with MCG-111 or silicone grease again?

 

[lexvil]

I found the best solution

 

[kdlv]

MK17 Evo is my primary. Still like the turret and simplicity of the MK10. Couple of O-rings in it and that's all.