Hi all.

I have a pair of LQ4s in a marine application. They have been good.

I have them out for a transom job, and I did some testing on them. It seems the valves are not sealing very well. I'm wondering if a switch to stainless valves is in order, but I don't know if they were perhaps stainless from the factory and I'm chasing my tail?

Here is the result of my compression and leakdown test:
comp leak down (80psi in) leak source
1 160 60 Mostly intake, some exhaust
2 145 28 Exhaust
3 180 72 Small exhaust/rings
4 175 68 Small Exhaust/rings
5 180 73 Small exhaust/rings
6 145 25 Exhaust
7 180 72 Small Intake/rings
8 210 68 Small exhaust/rings


My second engine is similar.


Thanks for any information of advice.

Chay

 

With a cranking pressure range from 145 to 210, I think at minimum a ball-HONE and set of rings is in your future.

 

Marine engines live in a harsh environment. I’ve done a lot of off shore big block stuff, as well as your run of the mill 350’s in a cruiser type deals. Corrosion is part of the equation, no matter what valve material you’re using. The seats that the valves are sitting on will have corrosion on them, after sitting for a while. We found this on every tear down. What we also found was that running the engine cleared things up. Get it up to temp and that corrosive layer will go away with heat and getting washed with fuel. I wouldn’t panic just yet, especially if it hasn’t been run this year yet.

 

Thanks for the posts gentlemen

I don’t think I have a ring issue as there is very little bypass into the block

i was wondering whether some heat and flow might get these valves to seal again, very much along the same lines as you have suggested

I think I will install them and see how it goes. I’ll test them again after some run time

Im not sure why I have a high reading on that one cylinder. Kinda strange for sure. Like someone stuck a domed position in one cylinder only. Have to think about it for a while


Chay

 

Try lapping the valves and see what comes of it.

I'm inclined to agree, having some experience with boats; especially if the boat was left in, or near, the water, over the winter. First spring startup can be a bit nasty, butt then it smooths out after an hour or 2.

 

If I can't get good results after running them I'll lap the valves for sure. I had lapped one engine in the past because it needed a hone and re-ring when I got it. It was a high miler. And I tested it after, so I know at least one of the engines had good valve sealing in the not too distant past.

I have a 'spare' 5.3 that was swapped into my '88 F body with the same 317 heads on it...I'm haven't taken it apart but it seems to have a rod knock. So I don't mind pulling the heads so I can prep those and swap, then prep the swapped ones...to lower the down time.

It won't be super fun to do in the boat, but it would be 'doable'. So it's time to roll the dice......

I have a second old boat with a 305 in it...I noticed the first start after 4 months was rough and like you said it smoothed out...Probably in about 10 minutes. Maybe I'll be that lucky again.


Chay