cct death buzz only when cruising

[turtlemann14]

so let me start off with, I am getting pretty annoyed with this.

back in 2019 I "had" to rebuild my engine due to sheared teeth on the timing belt. engine is stroked and bored. had a different head put on due to a superficial crack between the exhaust ports on cylinder 3.
I am running a fluid damper, ferra super alloy exhaust valves (not sure what valves were used on intake as it was an off the shelf head the shop happened to have), IE's spring and retainer kit with stock cams, new cam chain and cct.

the engine now has about 60k miles on it and is doing pretty well considering I lost oil pressure twice since the build (oil cooler and turbo feed line failed). oil pressure 14psi hot idle.

the major problem is that I have put two new cct on the engine since the build and the one that is currently in it is starting to rattle again.
I had one fail to the point that it could maintain control at idle and started slapping badly. the others have just developed a light load buzz between about 2-4krpm. sounds exactly like a heat shield going into and out of resonance.
all of the wear pads have had cavitation looking wear on them towards both ends of the pads. (I at first thought this to be a casting flaw such as porosity)
the stock unit lasted 282k miles, it amazes me that aftermarket can't make it 20k. surely this can't be common.

dates of replacement.
1/9/2019 ecs assembled
6/24/22 gates
1/30/24 vaico

tonight I got pissed off and decided to dissect the original cct from the build, an ecs assembled kit.
the findings are that it ate a seal and that most everything else looked ok.


gland bore
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piece of seal in port of pushing piston towards the head
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whats left of a seal in top of housing
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piston assembly
20240820_195127.jpg
piece of seal that came out of spool valve
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as you can tell a large chunk of green seal was plugging the port responsible for driving the cct down towards the head. there was a bunch of debris on top of the piston and in the spool valve as well.
I didn't find any debris on the tension side of the unit(check valve behind inlet screen should prevent this), but my theory is that once the seal in the top of the housing bore is gone the spool valve is getting caught on debris in a position that is in between settings and is blowing oil out of the exhaust port. another option looking at this particular one is that the seal is getting jammed in the port and not correctly pressurizing that side of the cylinder. this would allow the spring on the bottom side to pull air into the top half as the bottom vents oil. (cam advanced, no dampening or position control due to air in place of oil)

this seal may only be to buffer the piston to a resting position, as when the top half of the chamber is pressurized there is no seal on that part, just the clearance between the shaft and housing(when the piston is down towards the head).

i think tomorrow I'm going to pull the spool valve out of the one in the car and see if it has debris and if cleaning it will get rid of the buzz.

is there a solution to this?

btw bore on the cam tension part is 16.75mm this would put a max of 25lbs of extra force on the shoes at 73psi oil pressure.

[turtlemann14]

pulled the spool valve out last night, no debris in it. once it was back together I activated the solenoid. in doing so it buzzed/slapped for about 0.125-0.25 seconds as it changed the timing. total timing change took about 0.5-0.75 seconds.
is this just a low oil pressure issue? I found an article from vw now that says minimum is 1.2-1.7bar/17.4-24.65psi. I thought minimum was right about 14 psi at hot idle?
I am running 0-40 fs mobile1 and at cold start 70* day op is north of 60psi idle. hot running 4krpm its bout 60psi. hot 2krpm Im close to 40 psi.

I am also starting to question the temperature (considering what was left of the seal) of the oil but I don't have a good way other than an external probe taped to the cct to check it atm.

[turtlemann14]

It's was about 95 here today and I noticed my oil pressure was a bit low for comfort. by time I got to my garage, found my thermometer and probed the oil temp it was about 225*f Im assuming that since it was that temp after driving 50mph and though a neighborhood for about 15 minutes that oil temps on the interstate and especially while boosting and piston cooling jets are on could be cooking the seal. viton 400*F, hbnr/hsn 302*F both of these seal are green like the one that disintegrated.
if i had to guess the aftermarket units use the HNBR/HSN seal where to stock one uses the viton seal or something else.

so now do I bite the bullet and buy the stock cct? and also I need to sort out my high oil temps.

are these forums dead?

[turtlemann14]

assuming I did the test right, the specific gravity of the bit of seal that I found in the passage ways came out to 1.994.
viton specific gravety is said to be 1.7-1.9
hnbr specifit gravity is said to be 1.2

so this test says that the seal was viton and should handle 400*f

test: weight of seal in air 0.359g, weight of seal in 4*C/40*F water 0.180g

[turtlemann14]

I have done a little more digging and thinking. after unplugging the solenoid on the cct, most of the buzzing has stopped and all of it at 4krpm seems to have stopped(it was starting to get noticeably worse faster). since my 1.8t is in an a4 it's said to use variable cam timing.
after looking closely at the spool valve in the cct it can be in a position where both sides of the piston are exhausting the oil from both sides of the cylinders at the same time. once drained of oil this would allow the whole system to slap around uncontrollably and could be why the seal has failed like it's been through a rock crusher.

so now, what is the proper remedy?

is the solenoid on these digital(one position or the other) or is the driving signal of high enough frequency to float the solenoid and spool valve into a variable position?

I would think that it would be better to have oil pressure on both sides of the piston at the same time(hydraulically locked), and then open the return side of the spool valve to change position.
the timing on the part of the spool valve that controls the pressurized flow is fairly narrow but does appear to close off both sides at the same time. where as both ends have to be near their total travel to close off the return side of the spool valve.

[turtlemann14]

i made a new spool valve for the vaico cct that is still in the engine, this made a change to how the cct sounds, but didn't fix the problem.
i ordered a new cct from vaico and took the spool valve out, between the one that is currently in the engine and the new one, the spool valves are the same. but unfortunately the cct i took measurements from initially was machined differently enough i am surprised it worked as well as it did.

last time i pulled the spool valve out of the cct currently in the engine, i had to force it out as a piece of same seal that died in the other cct was lodged in the spool valve preventing it from coming out.

my plan now is to make a new spool valve with updated dimensions for the vaico unit that eliminates the outlet port overlap and increases the overlap of the pressure intel ports.
from the measurements i got, it looks like the outlet ports have 0.010" overlap while the pressure in port has 0.005" overlap.

this may seem trivial, but don't forget the both ends of the actuator cylinder do not have seals in them so both sides of the actuator can bleed off and pull air in past the housing/gland to rod fit causing a loss of control.

also, because this unit is sprung into the advanced timing. when you start the engine, it has to build oil pressure for it to run in "normal" timing, this helps bleed the air out of the bottom of the actuator cylinder(where because of gravity, it could trap air) every time you start it.

[turtlemann14]

well, the dying cct finally failed. this one failed to the point the bottom foot that holds the plastic pad fell off. (got super lucky i got it home before it fell out of position). the gland in the bottom was also hammer lose, but still retained.
oddly enough it seems the lighter in color pads seem to not cavitate like my others did.

new one of the same brand is back in and running fine. mileage is currently 345271 for reference.

with a little closer look. it looks like the bottom foot isn't welded or riveted on these. i could have sworn the one i cut apart was swedged over to rivet the foot on.

i hope to make a new spool valve for this one this week.

[turtlemann14]

im at 347k miles now and I can already hear a faint buzz when decelerating from about 4500rpm and if I roll on the throttle above 3500rpm while on the interstate.
I replaced the spool valve with a home made one and it seems to have quieted down some more. I may take the spool back out and narrow the part of the valve that controls the oil coming into the circuit. as I feel like it may still be dropping oil pressure during the transition between an advance and retard cylinder movent.

and another side note, might be placebo, it feels like the boost comes on a bit faster now. only explanation I have for that is it could be moving the cam angle faster with more direct control and less air in the system.