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[terry paget]

R706 FHD
I was changing the cam belt. I had locked the cams, removed the belt. Then I put the car into gear to hold the crank. Then  I was called away to do an urgent print job. Late tonight I tried to push the car into the garage. It was hard to push It was in gear. Oh dear. I suppose some valves were open and I have bent them.

7 years ago on a V6 with suspected bent valves I was advised to turn the crank 60 degrees from TDC, then turn all the cams by hand, and if they always had resistance, valves were OK. If at any point cam turned freely, then a valve was bent. Does this test work on an inline four, and how many degrees should I turn the crankshaft from TDC?

[Kevin Wood]

Oh, Dear! That's the danger with getting distracted on a job.

I would say the best course of action is to fit the belt and time it up, and see if the compression is OK. It's got to be the only sure method and, if it fails, you'll know which pot has the bent valves. I wouldn't say turning the cams would be conclusive.

Be careful on the position of the crank when you come to time it up, though. 60 or 90 degrees from TDC will be fine as a safe haven  (90 degrees is ideal for a 4 pot). Don't turn it through the "other" TDC position to bring it back into alignment (i.e. ONLY turn the crank 90 degrees from the safe position in whichever direction is required).

[chrisgixer]

Any valve marks in the top of the pistons. 1,3,5 bank is easiest, obviously.

[tunnie]

Any valve marks in the top of the pistons. 1,3,5 bank is easiest, obviously.

Given Terry's recent posts on 4pot cam belts, I'm assuming this is his 2.0 

[chrisgixer]

Any valve marks in the top of the pistons. 1,3,5 bank is easiest, obviously.

Given Terry's recent posts on 4pot cam belts, I'm assuming this is his 2.0 

Oh ok. 1,2,3,4 bank then.

[terry paget]

Thanks for the brisk response, Gentlemen. I have replaced the cam belt. I could now pop back on the aux belt, put in some water, and see if it runs on all four (yes, you are right, this is the car for which I researched water pumps). Or I could test compression. What is the best way of doing that - I guess I should disable fuel and ignition first.

[terry paget]

I replaced the bottom pulley and auxiliary belt, filled radiator with tap water, reconnected battery, and turned the key. Engine started. It idled all right, so I took it for my standard six mile test drive. It's OK!

I do not understand it, but never mind. I found the bottom pulley still more or less at TDC position this morning, which surprised me. Last night I did not manage to push it all the way into the garage, it seemed harder to push than usual. Wife could not help because she had a fall two weeks ago, badly bruised her knee, still walks with a limp and cannot drive yet. There is an attractive 2.5 estate on e-bay in Bristol which I quite fancied buying her, but cannot do so now.

The Bristol car has 4 new tyres and a new spare. I bet the rear wheel bearing in not as noisy as my 2.5 estate. Hmmmm.

[05omegav6]

Happy days

I left mine in gear doing my belt, and could figure out why I could barely turn the crank pulley a quarter turn

Must say it's quite tricky checking the valve clearances on a 2.8 XR4x4 in gear with the hand brake on

[Andy H]

I wonder if any of the valves are actually open on a 4 pot when it is at TDC 

Two of the pistons will be at TDC so those valves will be shut.

The other two will be at BDC: one will be at the end of its power stroke and opening/about to open the exhaust valve, the other will be at the end of its intake stroke and the inlet valve will be closing.

If any valves are open it seems they are not open far enough to make contact with the pistons.

[mrgreen]

i think with a four pot you have a little more lee-way as in you can slip a tooth and will still get away with it

[terry paget]

On a 3.0 V6 Omega I slipped 2 teeth in December 2005. It rattled loudly, but still ran. I took it apart, changed the cam belt and pulleys and re-timed it, and it worked perfectly. The car ran until 2011, when my daughter stuffed it up the back of a 4 X 4, writing it off.

[Kevin Wood]

I wonder if any of the valves are actually open on a 4 pot when it is at TDC 

Two of the pistons will be at TDC so those valves will be shut.

The other two will be at BDC: one will be at the end of its power stroke and opening/about to open the exhaust valve, the other will be at the end of its intake stroke and the inlet valve will be closing.

If any valves are open it seems they are not open far enough to make contact with the pistons.

The valve timing does have some overlap. One of the pots at TDC will be on its' compression stroke, so both valves closed. The other one will be in transition from exhaust to induction. Exhaust valve will stay open over TDC to allow purging of the exhaust gases due to the velocity of flow established down that port. The intake will start to open before TDC to make use of this flow to start drawing air into the combustion chamber. These positions are normal for TDC, however, so the amount of lift on each valve will be designed to offer sufficient clearance.

Now let's consider the two cylinders at BDC. One will be at the end of the induction stroke but the intake valve won't close until some way past BDC, again, because the velocity of flow set up in the port will cause it to keep flowing, so potential for valve damage there. The other will be at the start of the exhaust stroke with the exhaust valve starting to open. Again, potential for valve damage.

One other thing to consider is that the engine has hydraulic lifters. Where the valves have sat in the open position for some time, the lifters may well have "leaked down", reducing the valve lift to a safe value, so that may well have saved the day.

[tunnie]

Great news 

[TheBoy]

Sounds like you got away with it, great news