Engine knocking

[Ben]

Hi all, 

I've recently changed a cambelt on the rallyes engine and after idling twice for 5~10mins it started making a knocking noise. A couple of people have suggested it could be sticking lifters, but are they likely to suddenly stick after being ok at first?

Obviously I'm a bit worried that I may have made a mistake with the belt. I've taken the cover off to check its still tight and its as I left it. My crank pulley had spun on its rubber insert so I couldn't use this to time the engine, so I lined the woodruff key up to 90deg and locked the cams normally. I'm thinking that because I did it this way I may have got the crank a tooth out? Is this a possibility or would it be running really badly?

The other thing thats slightly different is the tension of the belt between the cams. It was quite slack on the old belt and once I'd fitted the new one it was tighter and equal with the long run of the belt, which I think is correct..

I don't have a good crank pulley to check the timing with, so I'm planning to lock off the cams and remove the spark plugs, then measure how far down each piston is to check they are all the same. Will this work? And is it an accurate enough way of checking the timings correct, or will piston heights be too close to tell at a tooth out?

I'm trying to add a video of it running, but photobucket's really not playing ball.


Thanks for any advice, Ben

[welshpug]

pistons should be mid stroke when pinned yes, so that would be a good indication of correct timing, as would aligning the woodruff key.

as for belt tension it will always be a little bit off on a worn belt as they do stretch, as long as you slackened off the cam pulley and made sure they could move easily when you tensioned the new belt all should be well.

[Jake]

https://flic.kr/p/TR3wVs

That's the video. Unsure if it will embed on here.


Sent from my iPhone using Tapatalk

[welshpug]

if you made a mistake when fitting the belt you would have a tap all the time, one thing to double check is that the crank bolt is done up tight enough, as this drives the oil pump.

tired tappets are not unheard of these days, and on a hot idle oil pressure will be lower especially on tired bearings, which will highlight a slightly sticking tappet, they can be dismantled and cleaned which will quieten most down.

[Ben]

pistons should be mid stroke when pinned yes, so that would be a good indication of correct timing, as would aligning the woodruff key.

as for belt tension it will always be a little bit off on a worn belt as they do stretch, as long as you slackened off the cam pulley and made sure they could move easily when you tensioned the new belt all should be well.

Ok I'll do that to check it then, I think if anything the woodruff key could have been slightly clockwise so its worth checking. 

Yes I did loosen the cams and cleaned them up so they moved easily, although they didn't really move when I tensioned the belt, but as I was happy with tension I left it.

---

https://flic.kr/p/TR3wVs

That's the video. Unsure if it will embed on here.


Sent from my iPhone using Tapatalk

Cheers Jake

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if you made a mistake when fitting the belt you would have a tap all the time, one thing to double check is that the crank bolt is done up tight enough, as this drives the oil pump.

tired tappets are not unheard of these days, and on a hot idle oil pressure will be lower especially on tired bearings, which will highlight a slightly sticking tappet, they can be dismantled and cleaned which will quieten most down.

Not sure what you mean about the crank bolt driving the pump? Isn't the pump driven by a chain directly off the crank? The bolt was done up to 120Nm though so should be good.

I may start it again then now its cold to see if the noise doesn't come back til its warmed up.

[fatlapit]

If its the earlier type of engine the correct torque is crucial to drive the oil pump. If its the later type its key wayed so has less of a chance of slipping

[Ben]

If its the earlier type of engine the correct torque is crucial to drive the oil pump. If its the later type its key wayed so has less of a chance of slipping

Surely none of the engines have a cambelt crank pulley without a key? If it slipped at all the timing would be out and the engine shagged..

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Anyhow the knocking has gone, must have been something that needed freeing up. Thanks for all suggestions and advice.

[cully]

If its the earlier type of engine the correct torque is crucial to drive the oil pump. If its the later type its key wayed so has less of a chance of slipping

Surely none of the engines have a cambelt crank pulley without a key? If it slipped at all the timing would be out and the engine shagged..

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the oil pump drive sprocket on the crank on the later engines was keywayed
early engines relied on the clamping force of the crank bolt to stop the oil pump drive sprocket spinning as it didnt have a keyway

[Ben]

If its the earlier type of engine the correct torque is crucial to drive the oil pump. If its the later type its key wayed so has less of a chance of slipping

Surely none of the engines have a cambelt crank pulley without a key? If it slipped at all the timing would be out and the engine shagged..

---

the oil pump drive sprocket on the crank on the later engines was keywayed
early engines relied on the clamping force of the crank bolt to stop the oil pump drive sprocket spinning as it didnt have a keyway

Ah I thought we were talking about the cambelt pulley not being keyed. Still I can't get my head around how the pump sprocket could be held by that bolt rather than a key, I'd have to see a diagram!

[welshpug]

its clamped between the crank and the timing pulley and the aux pulley, same as many many engines, the key is purely for location, no force is applied to it once the bolt is tightened.

there are many engines out there with no keys on the cams or crank pulley.