Outer Limits 4x4 Board

I just compression tested my 350 Chev in by boat & found no# 6 cylinder down to 90 psi. (did the oil in cyclinder test, no change)

1. 170 psi
2. 155
3. 160
4. 155
5. 160
6. 90
7. 170
8. 145

Im assuming the valves need attention.

Does anyone know how much it would be to have the valve seats replaced or whatever needs doing to be able to run unleaded instead of LRP ?

fair bit of variation of some of the others too :( start with the valve clearances, if it has bad valve seat recession it could be that there is a valve not closing fully on that cylinder.

can you just run a lead substitute or valvesaver type drip system instead of expensive head work? if it's not a race boat I'd just drive it to death.

I removed the rocker cover & kicked it over to the compression stroke & the rockers were just loose & not holding the valve down at all.

I could just use an additive but the reason for this thread is that i dont know how "exensive" the head work would be.

By the looks of it i have to re-seat the valves anyway.

Edit- double post

Should be able to get them done for$300-400 depending on condition of parts like the valve springs etc.
Valves cost about $12-18ea ex and $8-15 intakes these are what I use to pay a few years ago tufftrided valves or stianless one piece are the go.
What condition was the inside of the engine like oil gulgie or clean.

I havent pulled the engine down yet so dont know much about the inside, i do change the oil from time to time & recently used a oil flush before the last re fill.

One thing ive noticed is it does run a little cold as its cooling water is straight from the dam via the exhaust manifolds, always been that way.

I suppose one way to tell if its the valves is to swap the heads around & see if the problem moves.

fair bet your problem will be the valves , pull the head from the offending cyl. quick check would be once the heads off just pour abit of petrol diesel etc into the comb. chamber if the valves aren"t sealing fuel will leak through into the ports pretty quick.
providing your guides ,margin on valve head & valve seat recession are all ok just give it a valve grind . BTW the variation between your cylinders is still within allowable tolerences, bar the 90 psi .
If it's just a social ski boat I wouldn't worry about the inserts unless you have bad valve seat recession , it will go for years on unleaded with out any problems!

Heads are comming off tomorrow so i might swap them around & do the test again, if the problem moves it will be a valve problem.

Scout, you say the heads as is will be ok on unleaded without re seating them, why would this be the case ?

G'dayKev,
do a search " no more decent fuel? "
It's been explained before.
The valves should be reseated, what i meant was unless the seats are badly receeded don't waste your money on INSERTS.
Andrew