Deep knock at idle, any ideas?

[HairbearTE]

My money is now on rattling catalytic convertor innards, and he just can't work it out for himself.

This is a common occurance with ceramic cats. Mettalic cats are on average 50% more expensive but don't shatter when they kiss a speed hump. Cats should also be run-in properly too (15mins @ idle is enough) if you want them to last. I wonder how many garages do this?

[katanaman]

This is a common occurance with ceramic cats. Mettalic cats are on average 50% more expensive but don't shatter when they kiss a speed hump. Cats should also be run-in properly too (15mins @ idle is enough) if you want them to last. I wonder how many garages do this?

So how do you do this and run a cam in at the same time?

[The Original Tom]

This is a common occurance with ceramic cats. Mettalic cats are on average 50% more expensive but don't shatter when they kiss a speed hump. Cats should also be run-in properly too (15mins @ idle is enough) if you want them to last. I wonder how many garages do this?

So how do you do this and run a cam in at the same time?

The same way you run in a brand new engine - compromise.
I had a new cam, which requires treating rough to harden it up, and new main bearings and freshly-honed bores that require gentle treatment for a while.
All on a brand new set of carbs that were running god knows what mixture, and timing that could have been many degrees out!
I had to compromise with 5 mins of idle running, then opened it up for a thrash on the cam for 15 mins.
That said, I wonder how many SD1's etc and crate engines left the showroom/warehouse and were never 'run in' at all. These are probably running fine at 150k+ miles...

[katanaman]

there is another compromise because its not the bores that need bedding in gently its the pistons. The bores and rings actually need a bit stick very early on for them to bed in properly. Trouble is on the rover you will scuff your pistons unless your very careful trying this if its standard gear. Your right though as everything is at odds with each other.

[HairbearTE]

This is a common occurance with ceramic cats. Mettalic cats are on average 50% more expensive but don't shatter when they kiss a speed hump. Cats should also be run-in properly too (15mins @ idle is enough) if you want them to last. I wonder how many garages do this?

So how do you do this and run a cam in at the same time?

Good question, In fairness to the cat manufacturers 99+% of all cat replacements aren't accompanied by a cam change! I did a short course on catalytic converters at work and picked up a few interesting bits of info from it. The run in period is to break-in the cat gently at a temp lower than the usual operating temp (around 1600 degrees). I guess if you're building a new engine then you'd obviously run-in the engine before installing the new cat.

[Boosted LS1]

I lube the piston skirts but leave the rings and bores on the dry side so the rings bed in quick. This assumes the customer will start the engine soon after he gets it. Otherwise I lube the lot.

Boosted.