Once again I'm seeking knowledge.  I took out the spark plugs today as i was going to check the compression in my 272 that is in my 60's classic ski boat as I thought she wasn't pulling that hard on the weekend.  To my dismay the spark plug for #2 has been smashed off as per the photos.  The really surprising thing was that she was running really well and has been continually.  No misses or rough idle, happy to rev up to max 5800 if you push her but I don't have to when skiing and stay at about constant 4000 after the take off.

Back in March she dropped the exhaust pushrod for #2 twice as she had been sitting forgotten by th eprevious owner for 7 years, never started and must have had a sticky valve.  Both times when this happened the pushrod was recovered (hadn't fallen in), checked and luckily not bent, and replaced back in.  These occurances were about a week apart, not back to back.  All the rockers were rechecked and set at 19thou and haven't missed a beat since, with skiing every second weekend or so.

With my little experience (1st y block), I'm chasing a rough idea of what to look for and to do next.  Please forgive my stupidness, but I'm guessing the heads should be removed to have a look at the pistons and check the valves.  Is it worth doing the compression test before this too check each cylinder?  If so (as I haven't done one), should I leave the other spark plugs in while doing it or take them all out?  I've been reading here and see that it should be cold and with wot, with 4-5 on each cylinder, but I didn't see about the spark plugs in or out.  Should I turn her over by hand and feel in to check for any pieces etc in number 2?

Any advice is greatly appreciated as it looks like I have some work ahead of me.

Cheers WHITEY (Down Under as well)

i would recheck the valve clearance on # 2 that plug looks like a valve hit it if the piston had it would be smashed in not sideways like it is

Looks like the spark plug took a hit by something.  Examine the interior of the carburetor closely for any missing parts and especially around the fuel discharge nozzles.  At this point, I’d slowly turn the engine over so the #2 cylinder is at TDC and take a look inside the sparkplug hole for damage.  If it looks clear, then spin the engine over and listen for any strange noises.  Then a compression check. 

By the book, remove all the spark plugs and block the throttle in the wide open position when performing a cranking compression check.

If you have suitable compression and don’t have a bent valve, consider yourself lucky and just put another plug in it and go.

Carby was checked and nothing missing at all, and I have recently put a brand new carby on and nothing missing there as well.  On saturday (day before I pulled the plugs) we skied all day with no hiccups at all, missing etc, but just seemed to be lacking a bit of power hence I pulled the plugs. 

I definately think the plug got smashed back in march when she dropped the pushrod on exhaust valve, but very surprised that she's been running so well on 7 cylinders since then.   I'll wind her up to tdc on #2 and have a look and feel and complete a compression test and let you know how it goes.

Cheers  Whitey

Bought a new spark plug today for $3.45 so at least she will be running on eight cylinders for a change.

Did the compression test this arvo and got the bad news and it's no wonder she's been struggling.  Results as follows:

#1 -100psi, #2 - 60psi, #3 -100psi, #4 -100psi, #5 -72psi, #6 -110psi, #7 -100psi, #8 -105psi.

Now to start saving for the inevitable rebuild coming my way.  Surprising though I could not see / feel any damage to #2 piston and there was no bits in the chamber.  Have to take the good with the bad I suppose.   Possible plan is to take off the heads and check the chambers to see if there is any lip, and the possibility of putting in new rings.  Would also check all the valve seats as well while they're off.

Always happy to accept any advice!!

Cheers Whitey