Rhythmic tapping after cambelt change

[937carrera]

As title really. I have just done a cambelt change and there is a regular tapping on startup, deep rather than high pitched metallic.

It's the only thing I have done except for a fresh set of plugs. I have rechecked the timing and the camshafts are in the right place when number 1 is at TDC.

The car hasn't been run for a couple of weeks. is it just lack of oil to the hydraulic tappets which should cure itself if left running, or have I done something wrong ?

Cheers

[6n2stan]

Even after leaving my car for a month the tappets only rattled for about 5 seconds before they primed up. Is the oil in good condition and topped up?

[alexperkins]

As stan said. Also, give it a 5 minute run and see if it settles.

Can you record a video of the sound?

[937carrera]

The oil was full to the high level mark on the dipstick - I checked it after I had done air filter, fuel filter and plugs, and has probably only done 10,000 miles since it was last changed with a new oil filter.

I'll try and grab a video and post it.

With any luck the problem is the priming of the tappets and it will disappear while I taking the video. I was running out of time tonight and wanted to make sure the timing was still ok before I did any more damage if it was not.

Thanks

[6n2stan]

Another thought, are your spark plugs in tight? Ive heard some funny noises in the past with loose plugs.

[937carrera]

Plugs have been in and out, all fine, and I know from personal experience the resulting tractor sound effect when the threads on a plug fail and the whole thing gets ejected

Anyway, I have now been able to take a little video

http://937carrera.co.uk/VIDEO0012.MP4

I moved the camera around to see if it became louder or quieter as I moved it. Let me know what you think please, the 30 seconds for the video is probably the longest time I have run the engine for since doing the timing belts.

[6n2stan]

That doesn't sound as major as big ends for example. Does it sound like its misfiring if you listen at the tailpipe? I wonder if there is a stuck tappet so the cam is hitting it as opposed to sliding over it? Might be worth an engine flush?

[937carrera]

I'm glad you're confused as well.

The engine was running sweet as a nut before I did the timing belt, except for a bit of noise from the auxilliary belt pulley which has been fixed.There's no misfire, maybe I just need to be brave and let it run longer to get a bit of heat in, thin the oil and allow the pressure in the hydraulics to build

[937carrera]

Bit of an update:

I decided to take the belts back off and do the job again. Well, I didn't quite do all that, I essentially checked the belt routings and slackened the tensioners, then reset them, being very careful on the position of the adjusters, the pointers and torqueing the tensioners to spec.

After doing that I supported the engine on a jack and started her up before all the covers were back in place.

A slight rattle on startup for less than a couple of seconds and then she sounds sweet as a nut again. (better in real life than the video)

http://937carrera.co.uk/VIDEO0013.MP4

I didn't find anything obviously wrong, but there must have been

Any thoughts ?

[937carrera]

Curiouser and curiouser........

I put the aluminium engine mount bracket back on the block and started up. The tapping was back. Removed, sweet again, refixed, noise back, removed, sweet again.

I cannot see any evidence of contact onto the engine mount. Now I'm really confused.

[alexperkins]

Did you put it back onto the engine mount?

That mount is a hydro bearing. When they fail they can make noises

[937carrera]

No I didn't, I was deliberately just doing one component at a time from that point.

I have however found what the problem is and it's my fault, I know what I have done. I found it by doing something a bit naughty and used a screwdriver to flex the plastic belt cover while the engine was running (kids, please don't do this at home). I was able to make the noise appear at will. Here's what happened.

In preparation for removing the very tight crankshaft pulley wheel I not only put some penetrating oil on but used a butane torch to apply a little heat. The flame exited through the four holes that are there for people who have the special locking tool to hold the crankshaft pulley and melted the inner edge of the plastic cover in four places, each no more than 10mm wide.

Not to worry, it doesn't show, EXCEPT, by not removing the small amount of excess melted plastic it can now make contact with the rear of the crankshaft pulley wheel.

[6n2stan]

How strange, that had tappets written all over it! You did well to find that, must be a relief!

[937carrera]

Indeed it was, I had the wise old words of a proper (and very good) car engineer in my mind "if it was OK before, it's something you have done, you just need to find it"

I had two choices - grind the plastic off by using the crankshaft pulley, or do the job properly by removing the crankshaft pulley and plastic cover for proper clean up. Doing it the latter way gave me the knowledge that everything would be right on start up, and it was

This is the second one I have done and though I used heat on the first one there was no contact upon re-assembly. I'll refrain from doing that on the next one. Timing belts seem like a really easy job now.