Clonking/ crashing

[Wolvesboy]

Hi All,
Next on the list!
When I take my foot off the accelerator, letting her roll in gear, an awful clonk/crash noise has started- kind of lurching. Seems like the prop/ gearbox want to separate and the car seems to lurch. If I knock it out of gear then all ok. Seems ok accelerating, no noticeable whine but hard to really tell. I had the car up on jack stands, started, put in gear and revved - no clonking/ crashing noise like on the road. Free revving in/ out of gear is ok too.
I visually checked the prop & attached as expected.
Any ideas please?

[CerbWill]

First thought is propshaft to diff bolts.

[itsallyellow]

My money would be on the diff bolts or bushes or both.

Mike

[phazed]

2 gearbox mounts or rear diff mount, (pray it isn't that!).

[pmessling]

Check the engine mounts as well.

[Byker28i]

gearbox mount,sounds similar although worse as to when mine broke

[ukkid35]

There's no stress on the diff bushes when on axle stands, but still plenty in the prop shaft bolts

So my money is on the diff bushes

I thought the front bushes would be easy in comparison with the rear, which they are, but they are still bloody awkward

Here's a video of my half arsed efforts

https://youtu.be/ebDbimVx1tQ

[Wolvesboy]

Thanks fellas.
My prop bolts seem all good.
Whilst underneath last night, I noticed the gearbox was closer to one side than the other - maybe in moving the engine around for the removal of the manifolds ive bolted it back down “off square”? The engine mounts seemed a little off centre when I replaced them but I didn’t take much notice as still within the mount range!

[Adambul]

If you've had the manifolds off and have also slackened the engine mounts then check your exhaust manifolds aren't now vibrating against the chassis. I had this and it sounds and feels terrible, until you realise what it is. I just had to move the engine on the mounts slightly to correct.

[Wolvesboy]

Good point adambul,
closer inspection reveals a manifold is actually touching the gearbox! Plus the gearbox itself is definitely over to one side. Common sense says to me it should be dead set in the middle of the transmission tunnel.
I’m going to attempt to “reset” the engine alignment over the weekend - exhaust off, engine amount bolts, gearbox bolts as I did when removing the exhaust manifolds.

[Wolvesboy]

I re-aligned the engine mounts to what they were initially. There is a slight improvement on the hesitation/ stuttering/ banging etc. I’m now clutching at straws for the next step as it still occurs.
Gearbox mounts are ok and the noise is definitely in front of me so I think I can rule out the diff. I could not get the bloody drain bolt off anyways!
Having driven it further today I worked out the hesitation/ kind of crashing was at 1800 - 2000 revs each time (off throttle and also when slightly going back on too) so could it be my valve timing is out from my recent valve clearance attempts? Could it have jumped a tooth on the chain? I did let one of the toothed cogs slip off my bracket at one point but it went back on and the chain did not come off the cog that slipped. If it slipped a tooth on the crank below then surely the chain would have prevented the cog from going back on the cam? Or is the timing out so the usual hesitation spot at those revs is amplified? She purrs on tick-over and goes ballistic over 3k revs though and a tooth slip would surely not let this happen?
My recent new exhaust is also pretty restrictive I think - maybe too much so. The pops and bangs are virtually non existent. Could this be a factor also?

[Wolvesboy]

Having read a few cam timing posts I think mine might be drastically out and the crashing noise is extreme pinking, especially at the notorious 1800 to 2000 revs point.

Can someone please confirm that it is #2 TDC using lobes 7&8, then #1 TDC using lobes 1&2? I initially read it as using both rear lobes on each TDC?

Has anyone please got a photo of the bubble method to find TDC as it seems to be the most accurate? The first & last time I tried fitting a clear piece of hose with a film was a complete failure!

Thanks.

[Jhonno]

Wolvesboy said:

Having read a few cam timing posts I think mine might be drastically out and the crashing noise is extreme pinking, especially at the notorious 1800 to 2000 revs point.

Can someone please confirm that it is #2 TDC using lobes 7&8, then #1 TDC using lobes 1&2? I initially read it as using both rear lobes on each TDC?

Has anyone please got a photo of the bubble method to find TDC as it seems to be the most accurate? The first & last time I tried fitting a clear piece of hose with a film was a complete failure!

Thanks.

Bank#1 uses Cyl No.1 Bank#2 uses Cyl No.2..

Bubble method is great.. I just had to wrap a little tape round the end of the hose to help sealing.

Edited by Jhonno on Monday 11th March 16:03

[Wolvesboy]

Thanks

However, my big question not answered:
Which lobes to gauge when at TDC?

1. 2 cyl =l lobes 7&8
2. 1 cyl = lobes 1&2 or 7&8? ......... i was on the understanding it was the rear lobes for both banks but have read on these forums contrary to this.

[ukkid35]

Wolvesboy said:

When I take my foot off the accelerator, letting her roll in gear, an awful clonk/crash noise has started- kind of lurching.

This does not sound like pinking

My experience of pinking is at 2000 under acceleration, where the only way to stop it is to lift off slightly

It is much worse when the engine is hot, and more difficult to provoke when cold

However, you are right cam timing is critical, now that I have changed the cam timing to neutral with no advance (lifters level at TDC not 1.5mm diff) I have been unable to provoke any pinking

I will post a pic of the tubing I use later, it is basically the same diameter as a spark plug so it screws in, with a thinner piece of tubing to reduce the surface area of the film

Bubble may be a misnomer, because I am looking at the film within the tubing not outside, so that the surface area is a tiny fraction of the area of the piston surface

Once you have found TDC on the front piston of each bank it will be very clear which lifters are 'rocking'

[GT6k]

I cant really help with the clonking/crashing but iof the tune was off then the place where it would all go pear shaped would be lowish throttle opening at low revs. Mine had a fairly big flat spot at about 2000krevs as you can see from the attached which is the before and after of Jools remap



Sorry to hijack the thread but there is one aspect of this i don't understand. The manual goes into great detail about the safe position which is when the back cylinder on overlap. But but surely this means that front and back cylinders are all the way up the bore and therefore not very safe. I would have thought the safe position was quarter of a crankshaft turn from this position.

[Jhonno]

Wolvesboy said:

Thanks

However, my big question not answered:
Which lobes to gauge when at TDC?

1. 2 cyl =l lobes 7&8
2. 1 cyl = lobes 1&2 or 7&8? ......... i was on the understanding it was the rear lobes for both banks but have read on these forums contrary to this.

As per my post..

No.2 TDC uses No.2 lobes, No.1 TDC uses No.1 lobes..

[ukkid35]

GT6k said:

Sorry to hijack the thread but there is one aspect of this i don't understand. The manual goes into great detail about the safe position which is when the back cylinder on overlap. But but surely this means that front and back cylinders are all the way up the bore and therefore not very safe. I would have thought the safe position was quarter of a crankshaft turn from this position.

You are right the pistons are at TDC

It's safe in as much as it is safe to remove and install the cam, because it won't spin round due to the valve springs as you do so

It would be safe to spin the cam to check for valve clearances if the crank were 90 BTDC as you suggest, but that is not the recommended procedure because you would then struggle to get the cam timed again unless you had totally reliable timing marks for the cranks 90 BTDC position

[GT6k]

Paul, thanks it seems as if it is a belt an braces procedure to make sure the cam timing is preserved.

On the question of which cylinder to gauge, well if you are using the bubble method then the pipe needs to be on a closed cylinder at TDC and the front one is easiest to get at so yo would gauge the rear cylinder overlap. If you wanted to be clever you could reverse this or you could bubble from 2 and gauge three or the reverse.

I just did the bubble method re-timing on mine and found that they were already set for equal overlap. I spent an age doing the odd bank and then realised that after i had finished that the previously scribed lines on the cam/sprocket where exactly lined up. So on the other bank i put them together on the scribe lines then checked TDC and it was bang on equal overlap.

[Wolvesboy]

So...get #2 piston at TDC, #2 cylinder lobes should be on overlap. Then turn/ adjust the cam so the REAR two lobes are even (#8 cylinder).
Then.... repeat the process for the odd side begin using #1 cylinder TDC (lobes on overlap) then adjust cam so #7 cylinder lobes are even. Test, test and test again.

Someone please confirm that is the basic gyst of cam timing.