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Old 03-24-2021, 08:56 AM
v8volvo v8volvo is offline
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Default Hydraulic lifter and camshaft failure

This was not on a D24/T engine but on a closely related 4-cylinder VW diesel using identical lifters to what is found in the later series D24, D24T, D24TIC engines from roughly 1987 onward in most parts of the world except for the USA.

Figured I would share it for interest to those who have the later engines with hydraulic lifters. I had heard of this problem but never seen it myself before.

This is on my daily driver 2003 Volkswagen Jetta TDI. The engine still ran well but had developed a light valvetrain tap, then quickly afterwards also started to display an acoustic thumping/popping type noise audible in the intake tract (airbox), and then also began setting diagnostic faults in the computer related to insufficient EGR gas flow.

When I pulled off the valve cover I discovered one cam lobe was severely damaged and the corresponding lifter below it was destroyed, having been deeply worn all the way through the top. The lifter of course could no longer hold oil pressure, so in addition to the excess clearance caused by the heavy wear, it had sunk down and opened up a further huge clearance, notice in photos how it sits a good 3-4mm lower than the neighboring lifters. The #3 cylinder exhaust valve thus was probably only getting about 1/2 the intended lift, or less, and reduced duration as well. As a result the exhaust valve was closing too early on the exhaust stroke and causing residual pressure to remain in the cylinder, which was released into the intake when the intake valve opened, causing the popping sound and confusing the computer's EGR flow measurements.

No idea whether the issue started as a lifter failure or cam failure, and what the cause was -- materials issue, manufacturing flaw, somehow damaged previously by something that scored a surface and then led to further wear, etc. I would guess the issue started slowly but got rapidly worse as it proceeded. All 7 other lifters and lobes were still perfectly fine. I had to replace the cam and did all 8 new lifters as well.

But it was lucky timing since this lifter's internal parts were getting ready to pop out the top and wreak havoc around the inside of the head. Could have led to a seized cam, damaged head casting, stripped timing belt, etc and general engine failure.

Photos: https://photos.app.goo.gl/s6mHCrAjvgj3RUwPA

If you hear any valvetrain related noise on a hydraulic lifter equipped D24/T/IC engine, investigate and repair before serious damage is done!
86 745 D24T/ZF 345k lifted 2.5"
83 764 D24T/M46 155k
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Old 04-20-2021, 09:17 AM
ukvolvo ukvolvo is offline
Join Date: Feb 2021
Location: Uk-North
Vehicle: 940 d24tic
Posts: 46

Is that the valve tops poking out i see in the pictures?

Do they not drop into the bores? Does this mean valve stems are not mission impossible with the head on?

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