351 W Head Work

I have an '89 351W that seems to be a bit tired. It is only turning my 13X13 prop at 4000 RPM wide open (1 to 1 drive). I am hearing a hissing sound when I turn the engine over with the flame arrestor off. I have been told that is probably a leaky intake valve. the guy that owned the boat before me had the timing turned up to about 14-15 BTDC at idle, which may have damaged the valves. I am thinking about pulling the heads and taking them to a machine shop for a rebuild...and I started thinking why not get the heads port matched to my new Performer intake as well. My question is..will the new heads and increased flow wash out my bottom end. To my knowledge, the bottom end is still strong, but I havent been inside to check. The hour meter is broke, so I dont know the true hours.

Thanks
JB

When I said "washing out the bottom end" I meant is it likely that the increased compression could cause the original, aged bottom end (rings) to fail. I have heard this from a few people.

A local speed shop quoted me $450-$500 for the port match and head recondition. GT 40s are out of my budget.

While I am not a mechanic by any stretch, I have the ability to pull apart the top end and put it back together. One major plus to doing the top end is that I dont have to pull the motor. I dont have the equipment. The second is that I dont have the expertise to dismantle the bottom end of an engine.

What do you all think?

Thanks
JB

While the boat is no turd, I understand the point.

Define good compression. I have heard many different opinions on "good compression". The 15% rule seems to make sense to me. I have a cheap compression tester and all cylinders tested about 110 to 125. 110 seems low to me. I figure that my leaky valve is costing me about 400 rpm.

Thanks
JB

110 compression doesnt' sound to bad even for the low end. I always went by the 10 percent rule though, I don't know about everyone else. But like Eric said I would spray some oil in the spark plug hole and see how much if any that changes your numbers across the board.

87Bfn, recieved the e-mail, post some pics if you can or send them to darrin2078@verizon.net to my attention
   thanks eric

jb_dallas wrote: Thanks for the replies. I thought that GT40s cost alot more than $540...that seems like a good deal. Will the GT40s bolt up to my old PCM manifolds?

These are GT40p's which are a little different than the regular GT40's. The differences are well documented in this article as well as on this site (if you search). Several members here are using them (including myself) with no issues bolting up to the PCM manifolds.

Yes I did- I almost forgot about that. The GT40p's were original equipment on 5.0 (302) Explorers and Mountaineers, so they used the smaller (3/8"?) bolts. I had the machine shop take care of that when I had the valve job done.

Sounds like blow by on the pistons...Compression check tells part of the story so I would suggest doing a cylinder leak down test on each cylinder.That will tell you how well each cylinder holds the compression.

Also...How bad is the timing chain stretched?

With high hours If you have too much stretch in the chain say 10 degress then your base timing is off by the by that amount of stretch. Great loss of power right there.

With the base timing on that engine being 10 degrees BTDC then actualy you would be set a 0 degrees BTDC even though you are set at 10 degrees on the balancer.

Just a thought....Good Luck

Hoey. The crank can't stretch so if the strobe sez 10 degress, its ten degrees.

How many degrees "stretch" would you all say is normal wear and tear?

Thanks
JB

Yes, I had that chain jump conversation with a group on thehulltruth.com last year before I found this website. Either I am crazy, or the engine mysteriously got out of time last winter. Last year I couldnt start the engine to save my life...I tried everything...drained the gas, new plugs, new rotor, new dist cap, ect. Finally checked the timing and it was signifcantly retarded, not where I had set it last season. Long story short, I got it started and didnt really think much of the whole timing thing. Some of the guys on the other website were suggesting that the motor could have jumped a tooth...others said no way...some said it isnt an "interference engine"....others disagreed. Is it possible for an engine to jump time, owner adjusts the timing..and run fine (with power loss)?

Thanks
JB

jb, your chain will stretch, and i think the boat doc told you how to check it and another indication of stretch is when you are timing the engine and the mark on the balancer is bouncing that tells you there is some stretch in the chain. . first do a compression test at operating temp and that will tell you the condition of the motor. I had a problem today with a motor and 2 guys told me the cam was wiped out... I was skeptical, pulled the dipstick and no metal at all in the oil, it was hissing on the top end also fell on its face. DID a compression test and all normal 145/150 accross the board.
The compression test answered alot of my questions eliminating the could be this could be thats. it was on a truck and the converter ended up being clogged.
The moral of the story is if i listened to those 2 guys i would've torn that engine down and put it back together with the same problem. I wont tear into something until I am 100% sure I know the problem and to find the problem you have to diagnose it correctly or you'll only end up aggravated as hell

I haven't seen a motor that has jumped time ever run again with out realignment of the gears. If you were going to go through all that you might as well just change the chain and gears while your there. In fact boats are already loud enough, I would just spend a bit more money and go gear to gear and get rid of the chain. Not usually a good option in a car because of the noise the gear to gear makes. Just my opinion though.

jb dallas
save the money and instead buy a good double roller chain with matching sprockets, Sumitt has a good selection from cheap to hi dollar.
They sell a set for 69.95 to a hi of 150.00 save that money and spend it on an intake or ignition upgrade.
    boat dr............