604 engine question

[bmchone]

My friends 604 got a little too hot over the weekend. Well 250+, so ill say more than a little. But never pushed any water out of over flow. We cooled it back down to 215 but noticed like steam or white smoke coming from the breather tubes. Im thinking rings or blow by. Guessing we should also do a leakdown check as well. What are you thoughts? Thanks.

[brad hibbard]

leak down is an excellent idea----
I suggest removing the water neck from the intake so you can closely monitor the water during the leak down
with the waterneck removed and water level at the top of the intake any air passing into the cooling system during the leak down will be easily noticed

the white smoke or steam as you call it-- out of the breather is not necessarily bad
its common to have moisture in the oil and undoubtably the oil temp was very high and any moisture in the oil was boiling and showing steam out of the breathers

250+ is HOT--- but I have seen them survive after that

I suggest doing the leak down as described above and also re torqueing the heads
especially the short row below the headers

Brad

https://www.race-1.com

[Matt49]

At what amount of leak down should one consider having the motor freshened up?

[brad hibbard]

great discussion question Matt----------

depends on where the leakage is from

I described a procedure in my original post to watch for air leaking into the cooling system and with that procedure it does not matter what the number is ---if bubbles present when doing the test you must address the problem

but if there is no cooling system leak ----then there are 3 areas of leakage
Intake valve
Exhaust valve
Rings

as a number--- below 6% leakage is preferred
BUT
I have seen many engines in the high teens run very well

the one place I hate to see leakage and feel it has the most affect is an intake valve

exhaust valves commonly leak and although they will not get better with time (only worse) a ex. valve leaking in the teens has very little power influence

rings leaking in the low teens can be attributed to position of the piston---reposition and test again

I like to do my leak down with all the rockers off and a blow by gauge attached ----makes it easy to isolate the leak

hope that helps

Brad

https://www.race-1.com