Can this happen again?
 

I wanted some input before i ran the boat this weekend.
I have 2 509 BB. 500 HP large oval port 781 heads, EMI thunder exhaust, Crane cam 559 lift, 236 [email protected] LBA 114 edelbrock air gap manifold, msd ignition, initial base timing set at 14 and advance is 20 total 34 degrees.Last labor day 2010 I developed a water leak in a few exhaust ports on both engines..I have previous posts on white stuff under valve covers..I rebuilt both engines over the winter and installed 2 new sets of heads. I'm running 2 holley 4150 series 850 DP flowed to my specs..
The jets that the carb guys originally set it up with were 78 pri + 84 sec with a 6.5 PV in from and no PV in rear. I remember complaining to the carb shop about the boat eating so much fuel just cruising around 3200 rpms and a sooted transom each time I used it..I sent the carbs to them and they lowered the primary jet size down to 76 primary on one carb and the other to 75 primary.
My question is: Could the lowering of the jet size cause an excessive amount of heat in the cylinder heads , possibly causing cracks and the water leaks?. Pics enclosed..The valves without the white stains seem to be lean to me..
and should I raise the jets back to 78 or 77 primary.

Thanks

timing can do that as well....what did the plugs look like ? either lean, timing or water....

Its hard to say..they always looked tan but that could have been from idling.A few had rust on them. The old 781 heads had the bowls cut out for more airflow..On the new heads i told the shop to only install the bigger valves and not to cut the bowls out.. Everything i read about the 781 heads is that if you grind the bowl area you could get too close to the water jacket.. It seemed like the water was leaking from somewhere close to the valve guide area when i pressurized it

BBC valve guides go through the water jackets, so they can leak here if not properly installed. As you noted, it is also possible to get into the water jackets when enlarging the valve seats.

Have you verified that you are not having a reversion issue? I know your LSA is 114*, but 236* at .050 can cause reversion depending on the total overlap.

Have the exhaust manifolds been pressure checked?

If you have too much heat in the combustion chamber, it will sometimes show up as higher oil temps. If you don't have oil temp gages, it will show up as low oil pressure idling after a fast run.

Budman, These pics are last years before the rebuild.The exhaust manifolds are new 2 years old. There is no sign of failure or reversion.. I just had the risers off to fix the silent choice..No sign of water stains..As for the jet size , I contacted the carb shop and they said the carbs cam with 78 primary and 86 secondary..I replaced the primary back to 78's

Thanks

I have oil temp gauges.. 200 -225 at cruise and slightly higher after a hard run

20-50 amsoil oil also

Fixx
 

Emi's SS risers will condensate if theirs not enough heat in the water temps..run the boat and pull the risers and you may see white spots inside..

I appreciate all the answers..My question is based on the pics of my old heads..(see first post) Does any of the valves in the pics look like they were running lean..of couse not the one with the water stain...
I was running 3 sizes lower in primary jet size 75.
1-Could this be the cause of the lean condition and possibly cause the water leaks??
2-Do any of these valves look lean or do they look normal??

Water temp 155-160 thermostats 142's

Just for info I built a 505 and kind of followed the lines of the merc 460 cyclone which I have the manual on with all the specs. They ran a 850 dp on an aluminum dual plane. The jets called for in the manual are 84's front and rear. This is a 454 stroked 1/4" which made it 482 inches which they made back in the 80's. Only thing it has rectangular port heads if that makes a difference.

naw .... they never leak ......m


http://i829.photobucket.com/albums/z...s/P1000839.jpg


http://i829.photobucket.com/albums/z...P1000830-1.jpg

That looks like stock merc exhaust..My EMI's don't have water slots like yours show