Chevy 350

I would check the basic engine timing.

Use a dowel in a spark plug hole to find #1 TDC and be sure the flywheel timing is correct.

Then I would check the ignition to be sure you have not slipped a gear to fire #1.

Basic and free to do.

 

Assuming this is the engine you rebuilt a few months ago and I remember you were having problems when installing the pistons and bearings. The first thing if you have a knock would be what is the oil pressure. If you don't have an oil pressure gauge I would definitely install one temporarily a mechanical gauge would be best. If the problem is a rod bearing you will have very little oil pressure when the engine is hot and idling. Usually the knock will be at the top of the cylinder when the piston strikes the cylinder head and piston slap and will lesson as you advance the timing because firing the cylinder earlier keeps the connecting rod against the crankshaft at TDC. Usually the knock will go away when you open the throttle and be worse when you back it off. If the oil pressure is good then I would check to make sure the timing marks are correct. The best way to do this is with a stop plug in number one cylinder. You can make one with an old spark plug just break out the porcelain and weld in a bolt or piece of steel so that it will hit the piston and stop it when the motor is turned by hand. Make sure the piston is down when you screw it in. Turn the motor by hand until it stops against the plug in one direction make a chalk mark at zero degrees by the timing tag and then rotate it in the opposite direction until it stops and make another mark. If the the two marks are an equal distance from the original timing groove on the dampener then the timing tag and dampener are correct if not then 0 degrees is exactly half way between the two chalk marks.

 

Hi Dave T and Fast Fred,
Thank you both also for your ideas.
Looks like ive got a number of things to try.
Ill keep you all posted how it all goes.
And yes Dave T this is the same engine as you mentioned.
Just ironing out the final things
Cheers,
Mike

 

Hi all,
Ok so after work this arvo I have done the following as per suggestions

Found TDC on #1 and the timing tab and distributor are correct
Checked firing order again and this his correct

Checked oil pressure and this is running around 50

The sound is coming from around the #6 & #8 plug and on close inspection I could see a small amount exhaust fumes that must be coming from a hole in the under side of the riser and that seems to be the source of the noise

Would the engine make a popping sound thru the leak and would the noise get less has the timing is advanced ?

It's going to be a tricky job to fix the leak and I'm hoping that this is the source of the noise

Any thoughts please guys

Cheers
Mike

 

Where is this hole exactly? Riser, head, block, manifold?

 

Manifold
Lowest point where salt water would sit
I've always flushed engine with fresh water after using but who knows how well the previous did
Will see how big hole is tomorrow has engine was too hot to feel around
Im thinking it must be a small crack only as i checked for this before reinstalling the risers and they seemed fine

 

An exhaust leak can sound like a popping noise, if it's a small hole. A knock has a very different sound, much more metallic.

 

Get some JB Weld or similar epoxy putty-mix, and put it on as good as you can. Not to fix, but to see if that's the problem.

I was wondering if you have a lifter that's not pumped

 

Thanks Par / Westvanhan,
Ill let you know how I go

Cheers,
Mike

 

Hi All,
Update for you.
OK so I fixed the hole the exhaust manifold and the noise has gone.
Wouldn't have thought that such a bad noise would be caused by that.
Well you learn something every day I ques.
Thanks for all your input.
Cheers,
Mike

 

Ok so i took the boat out today and the patch job didn't work and blew out
The hole in in the position on the exhaust riser shown in the picture but it's in the exhaust port on number 8 not 2 in the picture
It on the under side of the round section I'm thinking this is where salt water sits if the engine is not flushed with fresh water
My question is the engine was running fine at low revs to get back to the boat ramp but if I tried anymore revs than 1300 rpm the engine stopped
Is this
Caused by the hole or is this telling me there is another problem ? ?
Thanks
Mike

 

A good welder can braze the hole closed. JB Weld (epoxy) and similar products will not work for very long (minutes).

 

Hi Par,
Yes ive got a good welder ive used before that ill ask if he can you this repair, im sure he will be able to.
Would this hole cause to engine to stop at revs above 1300rpm or is this something else ? ?
Thanks,
Mike

 

Are your manifolds aluminum??
Judging by the shine, they could be
If so, you can have someone tig the weld BUT any dirt, moisture, oil ANYTHING in the hole can cause the weld not to take AND if moisture can blow open the weld as the water expands.

Before I would risk welding this piece, and I have done a few, I would get about a 1/2 inch steel flat bar by 3 inches wide. mark out the holes on the exhaust manifold or use the gasket as a guide and make this piece capture all the bolt holes, You obviously must leave enough room to get the tig torch in to make the weld so you can cut out a relief there.

The reason is to try to limit the distortion when welding up the crack/hole. If you do not, the flanges can get out of line and perhaps the gasket will not seal. Then you will have to machine the surface to get things flat

We used Brakekleen to try to get rid of any junk in the crack/hole. Use it outside and let it sit about an hour after you clean the spot. Brakekleen and an arc ( if it is a trichloroethane base) is hazardous to you health

 

If an exhaust manifold is corroded through, it is time to replace it. The leaks will start on the inside, sooner or later and fill the engine with water.