mercruiser 7.4 big block knocking or popping through carb help needed

[xjdriver]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

You also need to make sure the valve that the broken push rod actuates is not seized and the rocker arm is not cracked or brocken.Or youll just bend the new one.

 

[NHGuy]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

As Chris said, the piece could have fallen down the oil return into the valley under the intake. Hopefully it's just sitting there. Remove the intake and have a look before you run the motor any more. Maybe you dodged the bullet!

 

[bonzoscott]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

I can't see a "push rod" breaking. Seen many bent, never broken. Which end was missing. If bottom, it's likely laying the valley. If top, likely laying top of the head. And usual cause of bent was collapsed lifter allowing play in the valve train.

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

thanks everyone . bonzo ask which part was broken, it was the bottom one inch broke off.
nhguy i realy hope i dodge the bullet on this one. xjdriver i will try an free up every with mystry oil pb blaster you name it before i run it again. after work tuesday before i get to play with it again.. thanks yalll i will keep posting.

 

[achris]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

Doesn't matter if it fell all the way to the oil pan. If it's in there, it's there for good. The oil pump won't pick it up. Once you have the intake off, I would be looking at replacing all the lifters. If one has collapsed, all are likely in a similar condition. And yes you can replace the lifters without pulling the heads. Just back the rockers off and lift the pushrods out, then use a hook to pull each lifter. Easy. Just make sure you put the pushrods back in their original positions, and adjust the rockers as per the book...

Chris......

 

[04fxdwgi]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

That sound is an intake valve leaking by, badly. Probably bent or stuck in the valve guide, which probably caused the pushrod to fail. Bending usually happens when engine hits a high rev condition and the lifter or valve spring "floats", causing the piston to hit the still open valve, bending the valve stem or valve head. This causes it not to seat properly, causing the severe valve leak you are hearing.

Seen it happen many times before. Valve bent, OR stuck in guide in an engine that sat for a long time causes pushrod to bend / break. Pushrod stub usually ends up sitting on head or in the lifter valley under the intake, more often than falling past cam and into pan. Have seen the pushrods pierce the rocker arms / valve covers (one even went though the hood) on SBC's before too. If stub did make it's way to oil pan, and you don't want to pull engine, just leave it there, as it'll just sit in the bottom of the pan, stuck in the sludge that's probably in there.

Sometimes, if just stuck, the valve can be freed up by applying mystery oil and thumping w/ a hammer (have done it on a clunker engine and lasted for years afterward). Personally, though, I would pull the engine, pull heads, do a valve job, pull pan and find the piece of push rod. But I would also check the bearings while in there too.

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

Lots of info thanks guys. Am still at work at the moment i just went to advance auto parts and perchase a few new push rods part number rp 3263 and big bittle of marble mystry oil n where do i need to poure the mmo to loisen up the valve thanks

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

after doing a lots of reading online last night guys i have one big q am thinking i might be the cause why the engine probly hydrolock amd broke the push . ok here is what i did , i connect the garden hose to the inlet hose of the belt driven water pump , mind the garden hose has a very high water presure because its coming straight from the main. i did turn on the water before i start the engine, so without the engine running the garden hose was already blasting away. would that cause water to gets inside num five cilinder. anyway tonight i went and strip the intake of all the hardware but i could not pry the intake off any tip , i

 

[achris]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

after doing a lots of reading online last night guys i have one big q am thinking i might be the cause why the engine probly hydrolock amd broke the push . ok here is what i did , i connect the garden hose to the inlet hose of the belt driven water pump , mind the garden hose has a very high water presure because its coming straight from the main. i did turn on the water before i start the engine, so without the engine running the garden hose was already blasting away. would that cause water to gets inside num five cilinder. anyway tonight i went and strip the intake of all the hardware but i could not pry the intake off any tip , i

Unless you have a corroded manifold/elbow or faulty gasket, no.

 

[04fxdwgi]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

after doing a lots of reading online last night guys i have one big q am thinking i might be the cause why the engine probly hydrolock amd broke the push . ok here is what i did , i connect the garden hose to the inlet hose of the belt driven water pump , mind the garden hose has a very high water presure because its coming straight from the main. i did turn on the water before i start the engine, so without the engine running the garden hose was already blasting away. would that cause water to gets inside num five cilinder. anyway tonight i went and strip the intake of all the hardware but i could not pry the intake off any tip , i

1st, see if the valve is stuck. With that piston at bottom dead center (or close to it) thump on the valve w/ a brass hammer and see if it moves. If it is moving, chances are the valve head is bent or badly burnt (or the seat is trashed) and valve or seat needs to be replaced. If it doesn't move, squirt the mystery oil anywhere you can to try to get it to wick to the valve stem. Lots of MMO won't hurt anything. Let it sit, then repeat w/ brass hammer.

From the sound of it in the video. it seems as as though it's time to pull the head (both of them) and do a valve job..

As far as getting intake to budge, ensure all bolts are out and use a putty knife between the intake and head surface in a few spots to break the gasket loose. Sometimes one will need to use a screw driver in the corner where the block meets the head. Once it moves a tiny bit, you got it. That intake is heavy and can take some "force" and still not be abused.

As far as water in #5 hole, that is a whole different problem. If it's substancial, then possibly cracked head, cracked intake (but that would show up in more than one, probably) cracked block, crack / pin hole in exhaust manifold..... The list goes on. Possible freeze damage....

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

update udate, i found the culprit . the problem is a frozen/rusted up valve on #5 cilinder i take the head of and bingo no matter how much mmo or rust buster i would have sprayed in that cilinder would not loose that valve up it is that bad. the lifters are working fine i turn the engine by hand and when the pusshrod comes up it just bend it up because the valve/spring was not compresing down. when i first got the boat i notice the engine has on two brand new risers, new stud ect. now i know what happen the previous owner did have a fail riser that dump water in the cilinde,r and they must have just install new risers and did not get the salt water out off the cilinder . could be a fail riser gasket too the manifold look almost new too. i will give the head the the mashine shop to get it done , am not even going to go crazy spending on this engine i will just get it running and see what happen i dont trust the previous owner on his word. want to say thanks much to all the great info u guys gave me and yall was on the money. now base on my serial number can someone points me to the part number for the correct intake and head gasket , i think it is oval port .. thanks

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

you kno what i dont even want the mashine shop try fixing this head base on how that port rusted up i think i migt get one off ebay. wher is the part numper located on the head there is so much numbers oll over it.

 

[Bondo]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

you kno what i dont even want the mashine shop try fixing this head base on how that port rusted up i think i migt get one off ebay. wher is the part numper located on the head there is so much numbers oll over it.

Ayuh,.... After a trip to the machine shop, you'd never know it was like that,....

If it's Junk, they'll tell ya so,...
Then find another 1, with Matchin' castin' numbers....

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

no bondo it still sitting in my truck , got to the shop too late so as u state if he said it junk i will just get another. ebay got a few on there just hope i get the correct one.

 

[HT32BSX115]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

no bondo it still sitting in my truck , got to the shop too late so as u state if he said it junk i will just get another. ebay got a few on there just hope i get the correct one.

Howdy,

I would take it to the machine shop and let them tell me it was junk.

After they clean it up you'll never know it was rusty. As long as it's not cracked, it'll be better than a used head because you'll know what you have.

I'd also pull both heads and have them rebuilt instead of just one.

 

[04fxdwgi]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

Glad ya got it figured out. Rebuilt heads are as good as it gets. They will change any bad valve guides (the part the valve rides in) and / or valve seats too. I have had dozens of pairs of heads rebuilt over the years and never had one fail. Just choose a good machine shop. Let the machine shop inspect / rebuild them or tell you they are a fancy door stop. They won't rebuild a junk head. You will be assured they are 100% OK or junk. I would absolutely do BOTH heads, that way you'll have even compression on both sides. After a head change / rebuild, the compression will definately change and you want it to change evenly across all engine holes..

Buying used ones may be as bad as the old ones, or worse. Don't ask how I can make a statement like that...

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

up date here guys,. just want to say thanks for telling me to go ahead and do the other head i took it off tonight and i was glad i did. now i realy need some re instalation info, i has not get my manual as yet.

# 1 what kind of permatex to use on the head bolt ?
# 2 should i put any permatex on the head gasket itself ?
# 3 is it ok to re used the head bolts. the ones that sits under the valve cover look real good
# 4 how much pound to torque the head bolt i lalready kno the bolt pattern .
# 5 what kind off gasket permatex to use on the intake i herd that is very important dont want water in the engin.

now i almost foget the new push rod i can get is just a hair shorter that the original i mean very close have to look real close to tell the diffrent.

 

[achris]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

ENGINE MANUAL

Download and SAVE it!

 

[04fxdwgi]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

up date here guys,. just want to say thanks for telling me to go ahead and do the other head i took it off tonight and i was glad i did. now i realy need some re instalation info, i has not get my manual as yet.

# 1 what kind of permatex to use on the head bolt ?
# 2 should i put any permatex on the head gasket itself ?
# 3 is it ok to re used the head bolts. the ones that sits under the valve cover look real good.
# 4 how much pound to torque the head bolt i lalready kno the bolt pattern .
# 5 what kind off gasket permatex to use on the intake i herd that is very important dont want water in the engin. Inow i almost foget the new push rod i can get is just a hair shorter that the original i mean very close have to look real close to tell the diffrent.

Here is what I do and have done for over 40 years with no failures and no ill effects.

# 1 what kind of permatex to use on the head bolt ? Do not use permatex on head bolts. Clean bolts with just oil on them to get a good even torque.

Note: Be sure to run a "thread chaser" or a thread tap down thru the head bolt holes and blow out the debris before putting on the heads. Those holes get rust and crap in them, making torque readings wrong. Always start with good, clean bolts and bolt holes or you risk a blown head gasket from bad torque settings..

# 2 should i put any permatex on the head gasket itself ? I use Permatex spray gasket sealer on head gasket, IF it isn't a permaseal gasket that has sealer on it already.

# 3 is it ok to re used the head bolts. the ones that sits under the valve cover look real good. Re-using head bolts on a BBC is OK, especially an older one.

# 4 how much pound to torque the head bolt i lalready kno the bolt pattern . Look that one up in manual.... But I always torque in 3 progressive steps, like: Torque all to 25 lbs, then torque all to 50 lbs, then torque all to final setting, but go around and do the final setting 2 or 3 times to be sure everything is even.

# 5 what kind off gasket permatex to use on the intake i herd that is very important dont want water in the engin. I use Permatex Aviator's gasket Sealer on intake gasket, especially around the intake runner / head ports, and silicone gasket sealer on the end gaskets, with a good dollop at the corners where the head, block and intake meet. never use silicone around the intake runner ports, as gasoline can break down the silicone and cause a vacuum leak

 

[bolo78910]

Re: mercruiser 7.4 big block knocking or popping through carb help needed

very important on the thread chaser i would never thought off that, what size for my bolt hole.

realy grateful for the help god bless.