The V8 Owners Forum -

Could a damaged cam (due to oil pressure loss) cause slightly low (15 psi down) compression on the rear most pair of cylinders?

I'm also hearing occaisonal missfires when idling and a bit of tappet noise.

Depends on exactly what is damaged.

journals ? lobes ? which lobes ? lifters ? other ?

Is the misfire on those cylinders ?

stevieturbo wrote: ↑Tue Aug 10, 2021 5:10 pm Depends on exactly what is damaged.

journals ? lobes ? which lobes ? lifters ? other ?

Is the misfire on those cylinders ?

Not 100% sure. The missfire is coming from the odd bank. Not sure how I'd find which cylinder is missing? Plug on 7 was a bit grot. (black and a oily)

I guess I colud put the strobe on each lead and see when it flashes in time with the missfire?

Misfiring exhaust should be cooler?

Take each lead off and see when it stops misfiring?

I'll try the last one!

I've seen some pretty worn cams and the only real symptom a lack of top end grunt. I doubt it would affect a cranking speed compression test.

In lieu of other equipment, this is a standalone and easy to use device to pinpoint misfires.

https://gtc.ca/product/gtc505-engine-ignition-analyzer/

Wideband info on both banks when running could help too, to identify if both banks are same, different, etc etc

The black oily plug isn't a clue ? Put a fresh plug in and run it for a couple of mins then remove plug and look for oil on plug . Also see if you cant see in thru plug hole
https://www.ebay.com/itm/372847986968?_ul=NZ

If you have tubular headers, measure the temperature of each, either with an IR thermometer, or use the old school method of spraying water on each and noting evaporation rates, notably cooler cylinders are where the problem is.

Well, No.7 is oily again after fitting a new plug and the misfires stops when you take that lead off..

Will have a look inside with the borescope!

rich112 wrote: ↑Fri Aug 13, 2021 10:24 pm Well, No.7 is oily again after fitting a new plug and the misfires stops when you take that lead off..

Will have a look inside with the borescope!

If it is oil, rather than fouled by unburnt fuel, then I'd be guessing at a broken piston ring. If you are certain it is not an ignition problem - faulty lead or cap.

Thunderchief wrote: ↑Fri Aug 13, 2021 12:06 pm If you have tubular headers, measure the temperature of each, either with an IR thermometer, or use the old school method of spraying water on each and noting evaporation rates, notably cooler cylinders are where the problem is.

This was my 'go-to' when I was getting occasional miss-fires. My stainless headers are wrapped with exhaust wrap so I can 'quickly' touch each and the one which doesn't 'singe' is the faulty cylinder! If you haven't got wrapped headers then a welding glove would probably work also! but yes an IR thermometer is 'safer' although with a shiny surface not very accurate.

The cam was knackered. Some minor vertical scores in the bores too. Rings all good.

Just about to check the valves now!