Crossflow Missfire and Engine Rattle

[88xflo]

Went for a quick blast this evening, car was running great; stopped for some fuel; pulled away and gave it a bit of a bootful; big missfire, popping and banging under load. Missfire went when I eased off, but there's an intermittent engine rattle, and a drop in power which co-incides with the rattle.

Had a look under bonnet; everything looks OK, oil pressure normal. manager to get home by going at steady 2000 rpm ish; at low, steady revs it sounded normal with  no re-occurence until pulling away or varying revs.

The only thing I can think of at present is timing chain / tensioner (have heard a duff timing chain before and I think this sounded a bit similar).

Quastions:

Any other ideas what this could be?

Could a duff chain / tensioner come on all of a sudden then be a bit intermittent?

Do crossflows have a timing chain tensioner?

Is the chain and tensioner easy to check / replace?

Many Thanks in advance of any advice, hoping this is'nt something more terminal.

Cheers,

Rob

[YouMustBeJoking]

When I had a similar problem on an MGB it was the vacuum advance in the distributor jamming.  This intermittently gave massive amounts of unwanted advance at high engine load and the rattle was the engine pinking.

[Andrew Mills]

Are you sure it wasn't just a bad batch of fuel.  Sounds suspicious that it started after you filled up and was pulling away from the station.

I have learnt the hard way to always check the easy, simple things first before going into expensive complex stuff.

Only a suggestion to add to the melting pot.

Andrew

[stu999]

Are you sure it wasn't just a bad batch of fuel.  Sounds suspicious that it started after you filled up and was pulling away from the station.

I have learnt the hard way to always check the easy, simple things first before going into expensive complex stuff.

Only a suggestion to add to the melting pot.

Andrew

Probably not, it would take a little while for the 'bad' batch to make it's way through.

Good call though...

I sincerely hope it isn't, and Andrews words are wise ones when he says check the simple things first, but the first thing I sadly thought about was a piston breaking up...

[chazpowerslide]

You did'nt put diesel in it did you?

And yes I have but it was in a 2CV and did'nt seem to make much difference

Chaz.

[88xflo]

Thanks for your responses guys:

I dont think its pinking, no vac advance, and it was a definate metallic rattle, rather than severe pinking; also did it at idle for a while.

Thought about the petrol, but there was a definate metal on metal rattle, which came and went, not just poor running.

Any more ideas?

Cheers,

Rob

[DickieB]

Maybe I misinterpreted what you're saying, but have you got a whole/crack in your exhaust manifold?  I took mine to a rolling road 'cos it was misfiring and popping/banging.  Turned out to be the exhaust manifold was cracked where 4 went into 2 pipes.

[88xflo]

Exahust manifold is OK.

Definately put super unleaded in not diesel.

The most worrying thing was the metallic rattle, this was'nt pinking, sounded more like a spanner rattling round inside the engine! Then went away completely, comes back when changing engine speed quickly.

[DickieB]

If it's only when under load, perhaps the engine mounts are weak, and something is rubbing under load - eg the exhaust manifold on a chassis member or similar?

[88xflo]

Dickie,

Thanks for help; engine mounts are almost new; the noise definatley sound like its "inside" the engine, and corresponds with power drop; it is now doing it intermittently at idle too, I am convincing my self that timing chain tensioner has somehow failed and chain is slack causing it to slap the timing cover and alter the valve timing hence the rough running.

I plant to strip down the front cover to check this theory; any other suggestions very gratefully received though.

[S8ight]

Then went away completely, comes back when changing engine speed quickly.

big end ?? if you blip the throttle does it rattle as you come off the throttle ??

dont see why this would cause pops etc ??

[Thrustyjust]

If you have a duplex chain and adjustable pulleys,then a tensioner is not needed.If you have a single chain,then tensioner is needed.If it has stretched that much,it would have probably sheared.

[88xflo]

Thanks for your advice.

Have had a look at camchain; was a bit stretched; replaced it today.

Have checked compressions:

1)160

2)145 to 150

3)160

4)160.

After the compression test I had a peer through the plugholes using a LED torch, 1 and 4 piston tops damp, 2 totally dry, 3 flooded with petrol; looks like I need to rebuild my dellorto's?

Could'nt run the car properly today as one of the water pump bolts sheared off (job for tomorrow morning). Did start it up for a few seconds, and it sounded fine.

I am totally mystified why I got the really ominous sounding rattle / clanking yesterday, ands why it was intermittent; when it happened oil pressure was very good; I think that a big end / piston sounds likely but that would'nt be intermittent would it?

This has got me totally confused; is there any possible way that serious intermittent fuelling problems could lead to dodgy metallic noises??

Any x flow experts out there?

BTW spec is fairly mild, 1630cc, mild cam and head work, 40 dellorts, lumenition optronic & big bore exhaust etc.

[Robandcolin]

I have a crossflow almost the same spec as yours.

A few weeks ago it started to rattle but only below 2k rpm. then it stopped  then it started again  

Although I've experieced no drop in power and no rough running  

It's not the big end bearing as there is no grumbling its not the timing chain and the compression is fine  

We came to the conclusion that its something like a sump baffle rattling around as it worse when the engines hot  

I haven't managed to check it out yet though.

Just a thought.

Rob

[88xflo]

Rob,

I found a thread written by someone with a Crossflow which was also making an intermittent clattering sound; seems the bendix drive on his inertia starter was faulty and was intermittently hitting the flywheel ring gear. I checked my starter and guess what, the ring that slides along the "corkscrew" thread of the bendix is shattered into four pieces, meaning that it is'nt always disengaging cleanly. The ends of the teeth also look pretty chewed.

Now this might explain the nasty clattering noise I have(here's hoping) but does'nt explain the backfiring etc. This was the first time the car had been out for a while and I'm hoping that the backfiring is down to either the carbs needing a rebuild (kits ordered) or dizzy cap and rotor, which look to have seen better days, (replacements ordered).

I'm hoping that when all of these little jobs are sorted, it'll be OK; but it still seems to be quite a coincidence that two seperate problems arise at the same time; I'm still concerned that there may be a piston / bearing related problem.

Cheers,

Rob