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CVVT cutaways

Help, Advice, Owners' Discussion and DIY Tutorials on Volvo's stylish, distinctive "P2" platform cars.

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jimmy57
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CVVT cutaways

Post by jimmy57 » Thu May 11, 2017 1:41 pm

A couple of CVVT pics with the axial piston forward and backward. It is always nice to see car part guts.
The piston has its seal missing as there should be an O ring in the groove.
The groove inside where the CVVT is fitted over the camshaft should also have an O ring.
Attachments
20170509_124856_resized.jpg
20170509_124847_resized.jpg

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Re: CVVT cutaways

Post by jonesg » Thu May 11, 2017 3:23 pm

OMG,
your wife is gonna kill you , using the cutting board like that.

Tonyx
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Re: CVVT cutaways

Post by Tonyx » Fri May 12, 2017 6:46 am

Interesting, thanks for the pictures. What I'm still trying to understand is why the angled gear has two opposing gear teeth angles. It makes more sense if there was one consistent angle to the teeth.
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Re: CVVT cutaways

Post by abscate » Fri May 12, 2017 8:03 am

It looks like the lower, driven gear (referencing the pictures) stays on one location on those teeth (you do wonder why it is even toothed, as Tony says) while the drive gear upper, slides and twists on the angled gear to give the required change in position of the cam as commanded by the ECU.

This is too cool. I always wondered how the oil pressure was used to implement cam timing and today, I am more educated than yesterday.

thanks jimmy
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Re: CVVT cutaways

Post by chrism » Fri May 12, 2017 9:35 am

Wow, I'm struggling to get my head wrapped around this one.....

It appears that the inboard (lower in the pic) gear is fixed to the piston, and the outboard (upper in the pic) gear is fixed to the cam shaft. So increased oil pressure pushes the piston and inboard gear outward, which causes them to advance approx one tooth in relation to the timing gear. At the same time, the piston and inboard gear are running over the outboard gear causing the outboard gear and cam shaft to advance approx one tooth in relation to the piston. So the net effect is that the outboard gear and cam shaft advance approx two teeth in relation to the timing gear. That's quite a bit.

In order to achieve the same amount of cam advance with a single gear, the tooth angle would have to be twice as steep.

Is my thinking advanced or retarded?

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Re: CVVT cutaways

Post by mrbrian200 » Fri May 12, 2017 11:54 am

Anchor the belt sprocket and twist the cam to demonstrate the mechanism in action. Back and fourth a couple times in 20 second video would be just awesome.

Referencing another thread:
viewtopic.php?t=79829
(VVTs Don't like Amsoil)

I can definitely see how seal swelling chemicals might interfere with the operation of these VVTs (motor oils that are known to be loaded with seal conditioning/swelling agents). That's a lot of sealing surface that needs to move: and not in a circular motion like a typical rotating shaft seal but slide laterally as a piston. Consider the oil pressure/VVT solenoids are PWM and the piston might start having trouble responding to minor incremental timing adjustments called by the ECU if those seals are swollen and tight.

Thank you a million times over for making that cutaway. Very useful from a general diagnostic standpoint to see what is inside of those hubs and how they work.
Last edited by mrbrian200 on Fri May 12, 2017 12:45 pm, edited 1 time in total.

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Re: CVVT cutaways

Post by cn90 » Fri May 12, 2017 12:18 pm

- Nice, thanks for the photos, beautiful!!!


- For cross-reference purposes, I posted some photos on the thread listed below on anatomy and operation of VVT (in a way this is similar to BMW Vanos system).

Large oil leak after replacing exhaust camshaft (cvvt) seal - help needed!
https://volvoforums.com/forum/volvo-xc9 ... ded-81251/
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Re: CVVT cutaways

Post by precopster » Sun May 14, 2017 10:50 pm

I had some CVVTs in a 2005 XC70 last week that had chronic leaking so I replaced them with used ones. The initial leaks were so bad I couldn't tell which CVVT was the culprit as you simply can't see back there and with the belt whizzing around sloshing more oil the whole area was covered, even after 3-4 minutes of running time after it had all been cleaned.

Upon replacement the new (used) ones leaked though not as badly and the issue was that I had set the cam seals to the same point as the factory had which is quite deep within the head. The used CVVTs had 2.5mm of play (old ones had 3mm+)

I reset the cam seals flush with the head and the area became bone dry so a steep learning curve is if you absolutely must fit used ones with some play you need to set the cam seal flush with the head.

From the pic I've attached you can see that leaking can be caused by one or more of 3 seals. Also if they're in tolerance of having less than 2mm of play you can rebuild them with new O rings if you can find the right quality and size of seal and use new cam seals set flush with the head.
Attachments
20170509_124847_resized.jpg
20170509_124847_resized.jpg (142.5 KiB) Viewed 886 times
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Re: CVVT cutaways

Post by chrism » Mon May 15, 2017 11:16 am

"...if they're in tolerance of having less than 2mm of play you can rebuild them with new O rings..."

Is that axial or redial play?

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Re: CVVT cutaways

Post by precopster » Mon May 15, 2017 5:21 pm

According to jimmy57 the official axial play is 0.5mm but in practical terms they can have up to about 3mm of play before the cam seal can't reach the outer lip.
Radial play is hard to measure as they have the natural rotational tolerance to adjust cam timing.
Current cars:2002 XC70, 2006 Ssangyong Rodius (Stavic), 2006 XC90 2.5T, VW Transporter 2.5TDI

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