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Timing belt replaced, low compression on all but ONE cylinder

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xApprchsNfnty
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Timing belt replaced, low compression on all but ONE cylinder

Post by xApprchsNfnty »

1999 Volvo V70 T5

Intake cam seal blew while driving, belt always remained intact/timed, car ran fine before disassembly. I locked the gears, removed sprockets/vvt hub, replaced front/rear seals, put back together, new belt/pump/tensioner/idler, serviced PCV (banjo bolt hole was clogged), replaced with updated check-valve bolt, and put it all back together. Belt installed with cams locked, VVT hub pre-loaded clockwise with timing marks lined up with engine cover, intake mark with engine cover, crank mark aligned, belt on, tension set. Turned engine over by hand many times before starting with only compression as resistance. It cranked but didn't start and plugs were fouled with fuel so I did a compression test: 2nd cylinder @ 150psi, every other cylinder @ 30-60psi. How did that happen?!

Timing marks:

Image

Image

Image

Leak down test performed, cyl#2 is fine, all others leaking 80+/- %. At the above marks, cyl#1 is almost at the top of it's compression stroke (is that where it's supposed to be when timing marks are aligned?) and when at TDC, it leaks slightly out of the brake booster port (vac hose detached). It does not leak out tailpipe nor out the oil cap/dipstick/coolant tank. Same behavior with cyl#4 but cyl#2 doesn't leak at all (I've only tested those cylinders).

Incorrect timing is the first assumption since I was working on those parts, but compression is only low in 4 out of 5 cylinders and if a cam were off-timed, then all cylinders should be consistently low, I would think. So bent valves possibly, but there is no instance to suggest when the valves were bent. Could I have sticking lifters or something preventing the valves from fully seating? It has only been about 2 months since the car was last driven.

Any and all thoughts are appreciated. There has been some discussion on this piggybacked on my previous thread here:
viewtopic.php?f=1&t=93339&p=540583#p540583
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Re: Timing belt replaced, low compression on all but ONE cylinder

Post by abscate »

Remember the timing marks are not TDC but the clearance mark, that is, the place where all pistons and all valves do not interfere regardless of cam position.

You have to index and reset the VVT hub with the rear cam locking tool, setting up the hub one tooth before the mark with the m4 bolts at max ccw position, installing torquinghub, then centering theM4s

It sounds like you got too far out and valves bent

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Re: Timing belt replaced, low compression on all but ONE cylinder

Post by befarrer »

Are you doing a compression test with engine cranking, or leak down test where you put air pressure into the cylinder? If you are doing the leak down test, are you testing all 5 cylinders with the engine timing marks alligned? If so then you have to rotate the engine so that the cylinder you are testing is at tdc on the compression stroke.
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Re: Timing belt replaced, low compression on all but ONE cylinder

Post by xApprchsNfnty »

Compression tested while cranking and leak down test with each cylinder at TDC.
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Re: Timing belt replaced, low compression on all but ONE cylinder

Post by scot850 »

Hopefully the valves are not dinged. Try a little oil in each cylinder before compression test. If reading goes up valves are most likely good. If they don't then either the timing is out so valves are slightly open on compression stroke or the valves are bent.

If adding oil makes compression go up you could have lawnmower syndrome. Look that one up.

Neil.
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