351 W Head Work
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=5563
Printed Date: November-27-2024 at 7:26pm
Topic: 351 W Head Work
Posted By: jb_dallas
Subject: 351 W Head Work
Date Posted: January-19-2007 at 12:01pm
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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 |
Replies:
Posted By: TRBenj
Date Posted: January-19-2007 at 12:37pm
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Minor head work like youre describing wouldnt have any adverse effects on performance. GT40's, GT40P's or any other upgraded head will still outflow them, and dont sacrifice low end.
I would find out how much it would cost to do the work. Having some port matching done in addition to a valve job will likely cost more than a new set of heads (GT40 or GT40P), especially if you have damaged valves. Before you start throwing money at the problem, I would do a little more diagnostic work. If the engine has other issues, changing out the heads may not do anything for you. ------------- |
Posted By: jb_dallas
Date Posted: January-19-2007 at 1:35pm
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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 |
Posted By: GottaSki
Date Posted: January-19-2007 at 1:43pm
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Don't polish a turd. If the turd has good compression, just run it and look for the missing power elsewhere. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: jb_dallas
Date Posted: January-19-2007 at 2:00pm
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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 |
Posted By: eric lavine
Date Posted: January-19-2007 at 2:02pm
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As the doctor checks your blood pressure and weight first a mechanic will check the compression first, if its good accross the board but on the low side and if you spray oil in through the plug holes and the compression comes up higher then it may need to be re-ringed also. cylinder wash is commonly caused from gas washing down the cylinder walls and the rings making contact with un-lubed walls. thats why todays fuel injected engines last longer, the fuel is atomized and completely burns unlike the carb which has a tendency to wash the walls ------------- "the things you own will start to own you" |
Posted By: 87BFN owner
Date Posted: January-19-2007 at 6:20pm
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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. ------------- |
Posted By: TRBenj
Date Posted: January-19-2007 at 8:28pm
A set of fully reconditioned GT40p's with a 5 angle valve job and upgraded springs are only $540 at http://www.tristatecylinderhead.com/catalog/product_info.php?products_id=40&osCsid=e5f88784700790742c3e1c250b1e73b7 - Tristate Cylinder Head. Seems like they would be $40 well spent. ------------- |
jb_dallas wrote:Posted By: eric lavine
Date Posted: January-19-2007 at 8:32pm
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87Bfn, recieved the e-mail, post some pics if you can or send them to darrin2078@verizon.net to my attention
thanks eric ------------- "the things you own will start to own you" |
Posted By: jb_dallas
Date Posted: January-22-2007 at 9:42am
| 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? |
Posted By: TRBenj
Date Posted: January-22-2007 at 10:00am
These are GT40p's which are a little different than the regular GT40's. The differences are well documented in http://www.stangpro.com/html/articles/gt40p_files/gt40p1.htm - 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.  ------------- |
Posted By: jb_dallas
Date Posted: January-22-2007 at 11:13am
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TRB
Did you have to drill the bolt holes out to 1/2"? I found a few threads that said it is necessary. Thanks JB |
Posted By: TRBenj
Date Posted: January-22-2007 at 11:32am
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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. ------------- |
Posted By: 81nautique
Date Posted: January-22-2007 at 11:57am
I recently bought a set of gt40p from Tristate and they drilled them out for 1/2" bolts at no charge. I just stated that they were going on a 351 and they took care of it. Make sure you factor in about $80 for shipping. Mine were $620 out the door. ------------- You can’t change the wind but you can adjust your sails |
Posted By: Seperator
Date Posted: January-22-2007 at 12:43pm
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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 ------------- |
Posted By: jb_dallas
Date Posted: January-22-2007 at 1:35pm
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Seperator, you bring up an interesting point. I have heard of timing chain stretch, but never thought it was very common. I wonder if that is why the guy that owned to boat before me had the timing turned up so high...or what appeared to be high according to the crank. I think I will do the "stretch test" soon.
Thanks JB |
Posted By: GottaSki
Date Posted: January-22-2007 at 2:08pm
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Hoey. The crank can't stretch so if the strobe sez 10 degress, its ten degrees. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: Seperator
Date Posted: January-22-2007 at 2:24pm
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Timing chain stretch is a common problem with engines that get over 800 hours or so. It throws of the ignition timing by the amount of chain stretch. People tend to try to compensate by advancing the timing.
I would be interested to know what yours is since you really dont know what the total # of hours are on the engine. Good luck ------------- |
Posted By: jb_dallas
Date Posted: January-22-2007 at 4:39pm
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How many degrees "stretch" would you all say is normal wear and tear?
Thanks JB |
Posted By: Seperator
Date Posted: January-22-2007 at 4:58pm
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It was recommended to keep optimum performance that anything more than a couple of 3 degrees stretch that the chain and gears be changed. That amount was usally seen at around 5-600 hours depending on the operation of the engine.It's a pretty easy job and it can be done right in the boat.
It really starts to cause problems when you get between 5-10 or more degrees stretch and you risk the chance of the chain slipping a tooth....Thats when things can turn real ugly......Cam goes goes out of timing with the crank...valves open when pistons are up...You can see where it is going with this....Can you say BOOM. Good luck ------------- |
Posted By: jb_dallas
Date Posted: January-22-2007 at 5:29pm
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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 |
Posted By: jb_dallas
Date Posted: January-22-2007 at 6:15pm
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I found part of my old thread on thehulltruth from last year. Here it is
Last night after it was dark, I hooked up a timing light. I dont know how it happened, but it was way off, about 5 to 10 degrees ATDC I moved it again to 10 degrees BTDC and tightened down the bolt. It actually fired for a second and then coughed and spuddered a bit. I pulled a plug and the spark looked strong and bluish in color.... 5 to 10 degrees ATDC is a big difference from 10 BTDC...if the chain did slip, I cant believe that it would have ran all season. |
Posted By: eric lavine
Date Posted: January-22-2007 at 7:46pm
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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 ------------- "the things you own will start to own you" |
Posted By: jb_dallas
Date Posted: January-23-2007 at 8:56am
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Thanks for the replies
I agree...my next step will be to check the chain stretch by the method described above by the dr. |
Posted By: 87BFN owner
Date Posted: January-23-2007 at 4:34pm
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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. ------------- |
Posted By: jb_dallas
Date Posted: January-25-2007 at 10:57am
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Has anyone else heard of running a gear to gear timing system on a marine engine?
Thanks JB |
Posted By: boat dr
Date Posted: January-25-2007 at 2:32pm
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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............ ------------- boat dr /diaries/details.asp?ID=4631 - 1949 Dart /diaries/details.asp?ID=1533 - 1964 American Skier |