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rob935
06-23-2009, 06:15 PM
looks like head gasket needs changing on my 93 351 , just wondering if it is a job to tackle myself as it seems as straight forward as removing the rocker covers , inlet manifold and head and just replace the gasket ?? what are the pit falls :confused::confused:

flipper
06-23-2009, 06:55 PM
Not much to it really if the head isn't warped or cracked from over heating or something. Just make sure you torque to specs

rob935
06-23-2009, 07:21 PM
where would i find the torque specs ??

etduc
06-23-2009, 07:37 PM
where would i find the torque specs ??

Chilton engine rebuild book.(Cheap) Torque specs are very specific, with Fords, even year to year.

Also, tightening pattern every important. Don't skimp, at this point, don't take guesses.

Use a good torque wrench. When I did my 1990 Tristar, with standard heads, it was a three step torqueing process. 75lbs, 95lbs, then final torque 125lbs.(NOTE: This may not be the correct torque values, for you.) The trick is, wait about 15 minutes, between steps. Old mechanic trick. Makes getting the final torque much easier.

Chicago190
06-23-2009, 09:44 PM
I think you'll also want to replace the head bolts. As I recall, most head bolts can not be reused as they actually stretch slightly when torqued.

denverd1
06-24-2009, 03:45 PM
Not too bad, i'm in the process of replacing them on mine right now. Second verifying torque specs. And use marine gaskets and new head bolts.

Etduc, Sounds like we need to go as far as reading the production code stamped into the lifter valley, then verifying with Chilton's manual?

JimN
06-24-2009, 04:05 PM
where would i find the torque specs ??

NAPA has them and if you buy FelPro gaskets, they have a torque pattern chart available. Also, they can usually tell you what the torque should be.

If the motor has overheated, especially recently, have the heads checked for flatness. If the motor has high hours on it, you might want to have them put the heads on a flow bench, too. This is the perfect time to make the motor breathe better and better breathing means more power/torque.

denverd1
06-24-2009, 04:12 PM
This is the perfect time to make the motor breathe better and better breathing means more power/torque.

Any shop worth their salt can really improve these heads.

etduc
06-25-2009, 12:40 PM
Not too bad, i'm in the process of replacing them on mine right now. Second verifying torque specs. And use marine gaskets and new head bolts.

Etduc, Sounds like we need to go as far as reading the production code stamped into the lifter valley, then verifying with Chilton's manual?

Go with what, JimN says. Exact engine year model, is all that is needed. As to specs...

I like to see things, in writing. NAPA,etc. Can get the info,

AND never-ever use an impact wrench, to tighten ANY engine bolt.

rob935
07-01-2009, 02:07 PM
hi guys , got boat home yesterday and set about taking the heads off to check the head gaskets , stripped them out and expected to see a shredded gasket but no such luck !!
both gaskets are intact so im not entirely sure if ive got a problem elsewhere , checked both heads out neither are warped . found some sludge in the intake manifold but was only a tiny amount , any feed back would be great thanks .

AFX-30
07-01-2009, 03:10 PM
Do not take the head gasket looking ok as the truth. I have pulled several that looked fine but were bad. replace them and retorque everything. Run the motor and keep an eye on the oil to make sure no water is getting back in the system. One thing I have always done after replaceing head gaskets is run it for a lil while then change the oil after the first outing if everythng was alright.

CameronCarey
07-01-2009, 03:16 PM
Id check the Cyls for scoring and check the valves for leakage, you can do this a lot of ways........i prefer to just pour rubbing alcohol into the ports and see if the leak (once your done you need to spray some wd 40 in them to stop any corrosion if you didn't find any leaks)

Blown head gaskets are not always terribly obvious but usually you can see where any leak occurred on the block face or head, if you cant............pull the intake too and check the lifter valleys to make sure there are no cracks running fore aft on the block.

if all that checks out, get a new set of head bolts and Marine gaskets and re-install it. if you PM me i will be happy to share with you the service info on that PCM engine.

Good luck

rob935
07-04-2009, 09:46 AM
thanks for all the help guys , took the head to the shop yesterday and it needs to be skimmed , had it pressure tested and getting the valves redone too, hope to be back on the lake mid july.:D:D:D

mbeach
07-04-2009, 10:53 AM
some very good advice here. also, i believe the head must be retorqued in a certain order but the book referenced earlier can verify.

André
07-04-2009, 01:10 PM
Would emptying the manifolds before removal would be a good advice?:confused:
I vaguely remember BriEOD having dropped water in the block when removing them...
Took a couples of oil changes to get it all out.

JimN
07-04-2009, 01:27 PM
Would emptying the manifolds before removal would be a good advice?:confused:
I vaguely remember BriEOD having dropped water in the block when removing them...
Took a couples of oil changes to get it all out.

Remove the manifolds and drain the motor before starting. The intake manifold has water in it and that's probably where most of it will come from. You'll need to remove that first, anyway so if it's drained, it'll be cleaner. If you have a compressor, blow air into one of the hoses to clear out as much as possible before removing anything and watch for water draining from the block plugs (I recommend replacing the petcocks with plain plugs).

rob935
07-04-2009, 07:13 PM
i drained the manifolds but didnt think to empty the block..., ended up with h2o in the cylinder but got it out straight away , have drained the oil out and plan to change it out again first run after heads go back on .

denverd1
07-06-2009, 08:38 AM
Spray a little wd40 in the cylinder and turn it over a few times to keep that cylinder clean. If you got a lot of water, run diesel through it to flush it out.

SappDad
06-23-2010, 07:04 PM
Hello Guys, I am going through the same thing this week. 130 psi on all cylinders except the back two on the drivers side: 25 psi each. Boat has been running crappy on takeoff and temperature has been creeping up. Last week it made the "brappppp" noise on takeoff for the first time: hence the compression test.

I appreciate all the info you have provided in this thread. Can anybody state one-way-or-other if the head bolts really need to be replaced? I have always heard this also, but of the several manuals I have read, none of them specifically say to use NEW bolts. All just say to be carefull with the torque procedure.

Also, is it common practice to vat the exhaust manifolds while they are off? Or is it a "how does it look" decision?

Finally, while the heads are being decked and ground, what "modifications" should I ask for to enhance the performance? Thanks a lot. I look forward to hearing your input.

thatsmrmastercraft
06-23-2010, 08:35 PM
Use new bolts. Bolts stretch when torqued, and the second time around won't be the same as the first. All you get for saving a few dollars is a much greater chance to do it all over again when you lose a head gasket due to the torque not being right.

JimN
06-23-2010, 10:24 PM
Hello Guys, I am going through the same thing this week. 130 psi on all cylinders except the back two on the drivers side: 25 psi each. Boat has been running crappy on takeoff and temperature has been creeping up. Last week it made the "brappppp" noise on takeoff for the first time: hence the compression test.

I appreciate all the info you have provided in this thread. Can anybody state one-way-or-other if the head bolts really need to be replaced? I have always heard this also, but of the several manuals I have read, none of them specifically say to use NEW bolts. All just say to be carefull with the torque procedure.

Also, is it common practice to vat the exhaust manifolds while they are off? Or is it a "how does it look" decision?

Finally, while the heads are being decked and ground, what "modifications" should I ask for to enhance the performance? Thanks a lot. I look forward to hearing your input.

Replace the head bolts. Torque is critical and if the bolts are work-hardened, the reading will never be accurate and they won't hold the way they're supposed to. A bolt uses the friction at the shoulder of the bolt head, friction at the thread and tension in the shank. That tension relies on the shank stretching a bit and it's very similar to stretching a rubber band- before it gets to a certain point, it still stretches but when it reaches that point, it doesn't stretch very much. That's where the bolts do their work, not when it still stretches. If the bolt can't stretch at all because it has become hardened, it will fail prematurely.

If the heads are warped, they may need to shave more than normal- if they take off more than about .007", the compression will increase. Not necessarily a bad thing if you plan for it and tune the motor accordingly. Valve job, possibly new rocker arms/springs and seals, too.

What is 'vat', pressure test? That can be done in other ways but if it's easier, go ahead.

SappDad
06-25-2010, 05:33 PM
"Vat" is perhaps an older term to indicate soaking the part in a cleaner bath. Generally used at radiator shops and such. I have been told that the exhaust manifolds get crudded up and should be cleaned whenever removed.

I've been told by a materials engineer that 120 pounds of torque on a 1/2 grade 8 bolt would not stretch the bolt past the plastic limit. Hence, the material properties of the bolt should not be decreased. I was advised that if they looked OK, it would be fine to reuse them. Both machine shops said the same thing.

I agree that on the surface "replace the bolts" is the obvious thing to do. BUT, by continuing down the "just a few dollars more" path makes a minimal $125 task into a $400 rebuild. (If one gasket blew, the other is probably not far behind, for $45 I can do both. While I have both off, for 'only' $85 each I can get the heads rebuilt. While I have the heads rebuilt, for 'only' $$$ more, I can get the lifters cleaned and checked. While I'm doing that, for 'only' $$$ more I can get the pushrods checked. While everything is apart, for 'only' $100, I can replace the intake with a cool Edelbrock one. For 'only' $100 more, I could put a mild cam in it. . . . and so it goes!) The head bolt kit is about $50, so if they really don't need to be replaced, why spend it?

The Fel-Pro head gasket says to replace the locator pins, but doesn't say anything about replacing the head bolts. I want to know if anybody has seen anything written anywhere to support the "common knowledge" of replacing them.

Anyway, any input would be appreciated.

1redTA
06-25-2010, 07:09 PM
replacing the head bolts is a common thing on an engine rebuild but I think it depends on the type of bolts used like torque to yeild or just regular torque to this ft/lbs

JimN
06-26-2010, 02:48 AM
"Vat" is perhaps an older term to indicate soaking the part in a cleaner bath. Generally used at radiator shops and such. I have been told that the exhaust manifolds get crudded up and should be cleaned whenever removed.

I've been told by a materials engineer that 120 pounds of torque on a 1/2 grade 8 bolt would not stretch the bolt past the plastic limit. Hence, the material properties of the bolt should not be decreased. I was advised that if they looked OK, it would be fine to reuse them. Both machine shops said the same thing.

I agree that on the surface "replace the bolts" is the obvious thing to do. BUT, by continuing down the "just a few dollars more" path makes a minimal $125 task into a $400 rebuild. (If one gasket blew, the other is probably not far behind, for $45 I can do both. While I have both off, for 'only' $85 each I can get the heads rebuilt. While I have the heads rebuilt, for 'only' $$$ more, I can get the lifters cleaned and checked. While I'm doing that, for 'only' $$$ more I can get the pushrods checked. While everything is apart, for 'only' $100, I can replace the intake with a cool Edelbrock one. For 'only' $100 more, I could put a mild cam in it. . . . and so it goes!) The head bolt kit is about $50, so if they really don't need to be replaced, why spend it?

The Fel-Pro head gasket says to replace the locator pins, but doesn't say anything about replacing the head bolts. I want to know if anybody has seen anything written anywhere to support the "common knowledge" of replacing them.

Anyway, any input would be appreciated.

It's less a matter of how much torque than how many times and how severs they have been heat cycled.