My '85 MGM, "Maisa"

[sly]

They don't typically have any interface material at the exhaust flanges on the manifolds. They do have the gasket at the H-pipe to cats location though. If yours is leaking from the manifold flange, the surfaces aren't interfacing well. Too much rust or maybe a dent?

Double check the firing order and timing. RPM at idle at operating temp should be about 650 IIRC.

Lopo firing order: 1-5-4-2-6-3-7-8
HO/351 firing order: 1-3-7-2-6-5-4-8

[Arquemann]

They don't typically have any interface material at the exhaust flanges on the manifolds. They do have the gasket at the H-pipe to cats location though. If yours is leaking from the manifold flange, the surfaces aren't interfacing well. Too much rust or maybe a dent?

Double check the firing order and timing. RPM at idle at operating temp should be about 650 IIRC.

Lopo firing order: 1-5-4-2-6-3-7-8
HO/351 firing order: 1-3-7-2-6-5-4-8

I highly doubt I have any basics related issues, I've gone through everything and anything that I can think of. Engine runs great, just makes a helluva racket.

The manifold to head flanges were block sanded before install with new quality gaskets, they're not great. I can't feel any leaks from the tops or sides of the exhaust ports. Didn't seem to leak before re-dismantling the engine and I didn't remove the manifolds off the engine last time.

Probably is the manifold to cat joint that leaks. I did inspect them, no visible issues atleast. Kinda hard to put goop on them, any extra bits would go into the cats. Dunno if I could've clocked them wrong, there's not much adjustment that way, mainly avoid hitting the frame. The end on the manifold looks like it could accept a donut gasket, but the ball flange on the cat pipe is too small.

[Arquemann]

Here's a video clip of my "diesel" 302 in action, vol 2.

https://drive.google.com/file/d/1MBRzMFSQUuR__jiKJEt6zu7RyoEY2iRH/view?usp=sharing

[sly]

Sounds like every lopo/truck engine I've ever dealt with. I say run it. It should quiet down a little as things seat in. That may take several thousand miles though. Also, it could just be the timing chain initial wear in. Is the sound louder at the front of the engine than the rear? (Mechanic stethoscope would help with this - poke the timing cover behind the water pump on the driver side (nice clear access point away from moving bits) and then poke somewhere in the rear like the bell housing)

The sound kind of reminds me of the timing gear noise from a Ford 300 big six.

[Arquemann]

Sounds like every lopo/truck engine I've ever dealt with. I say run it. It should quiet down a little as things seat in. That may take several thousand miles though. Also, it could just be the timing chain initial wear in. Is the sound louder at the front of the engine than the rear? (Mechanic stethoscope would help with this - poke the timing cover behind the water pump on the driver side (nice clear access point away from moving bits) and then poke somewhere in the rear like the bell housing)

The sound kind of reminds me of the timing gear noise from a Ford 300 big six.

Timing chain has about 7000 miles on it, done in 2019 so I reused it.
Noise might be coming more from the front, hard to say by ear. Probably should get my hands on a stethoscope, tire iron hasn't worked much better than without anything.

[sly]

Then yeah... I got nothing. Yeah, it's louder than some engines for sure, but it also doesn't sound different in tone. Strange.

[Arquemann]

Surprisingly the pass. side manifold-cat flange doesn't seem to be leaking, I can't really feel anything, maybe the slightest hint of a leak. Tried jamming my finger up between the block and manifold, but can't feel anything leaking from there either.
But the flanges between the Y-pipe and cats are totally blown out already. I had previously slathered the joint with fiber-reinforced exhaust putty, taken it apart, filed the surfaces flat and re-gooped them with gaskets and they've blown out totally in like 20 minutes of runtime. The rearward cat flanges and Y-pipe flanges are garbage and completely shot, honestly everything between the tailpipe and manifolds should be redone. Too bad it's expensive to get it done custom, shipping exhaust parts is ridiculous anyways.

Prolly going to remove the pass side cat pipe, make sure the manifold flange isn't leaking, goop up and double gasket the y-pipe flange and reinstall. Exhausts suck. And blow.

[sly]

Yeah... I had to weld the part between the cats and H pipe of my exhaust up even with new parts. That joint is just crap. As a temporary fix, you could cut the flanges off and use a clamp on exhaust coupler if those are allowed over there.

[Arquemann]

Yeah... I had to weld the part between the cats and H pipe of my exhaust up even with new parts. That joint is just crap. As a temporary fix, you could cut the flanges off and use a clamp on exhaust coupler if those are allowed over there.

Not a bad idea at all! Though I'll have to measure if there's enough straight section of pipe to be able to slide a clamp coupler on and off the joint, since there's not much back and forth movement in the Y-pipe and tail section.

[Arquemann]

Progress! I think?

On a cold start the rattle is very quiet, pretty much indistinguishable over the high cold idle noises. As the engine settles to a lower idle and starts warming up, the rattle starts getting louder and louder. I had it running for about 10 minutes, and held up the revs for some time, but it definitely wasn't all the way to normal operating temps. Even so, the rattle is noticeably quieter than previously, as in somewhere around concerning, instead of obnoxious.

So what I did to achieve this noticeable change in rattle volume? I changed back to the original motor mounts. The chinesium mounts must've been defective (or just garbage altogether), and transmit a lot of the engine noise into the frame and body, which seem to have functioned as a megaphone to the rattle. The vibrations felt leaning on the fender and sitting in the car are also reduced by quite a bit.

A couple things worth mentioning:
- Every time the engine has sat long enough to cool down all the way, the lifters clatter loudly for the first few seconds. Seems like they're bleeding down quite fast.
- There's sometimes a more persistent tick after startup, it has changed place twice now, so it hasn't been an exhaust leak.
- I installed a cheapo mechanical oil pressure gauge for sanity's sake. On 20W-50 the pressure was 60psi on cold start and went down to about 55-56psi after ~15 minutes of running.
- Engine seems somewhat shaky and vibrating on idle and on slight throttle, idle exhaust note sounds fine, no popping, plopping or puffing sounds.

From these things I've made 2 possible conclusions, shit lifters or poor oil flow to the lifters.
- The latter one doesn't have much to back it up, nothing should be impeding oil flow to them and if there were any debris blocking a passage or couple, the rattle should have a slower tempo.
- Cold and thick oil probably keeps the lifters quiet for a short while, before it starts getting warm and flows easier.
- Still don't know why there wasn't a rattle upon first start and 30 min of running after the engine rebuild.
- This causes concern as I do not know if the rattle is coming from the cam and rollers eating eachother or just the plungers not staying pumped up properly.

[friskyfrankie]

Is the factory recommendation 10W30? I understand you have used a heavier oil perhaps for another purpose. Could it be the present oil is too thick to get everywhere and that is the issue?

[Arquemann]

Is the factory recommendation 10W30? I understand you have used a heavier oil perhaps for another purpose. Could it be the present oil is too thick to get everywhere and that is the issue?

The symptoms would almost indicate the opposite, it's quietest when the oil is the thickest.
It has 20W50 in it just as a why-not-try and because it was on discount. The rattle was the same with 5W30 previously. Also this is a factory spec Ford small block, hardly a high-precision - low tolerance engine.

[gadget73]

How freely did the lifters move in the bores? If they didn't slide in easily that might be it. If they fall in there like a hot dog in a hallway thats not good either. The oil feed is a drilling that runs through the length of the lifter galley with a hole roughly mid-way up the hole. There is a necked down area in the middle of the lifter where it actually gets oil in, and whatever isn't required for the lifter itself flows around to the next hole down. if the bores are worn out or the lifters are undersized, instead of pumping oil through each lifter it will just piss out around the lifter and some won't pump up correctly.


if they sit real tight it may be binding a bit and forcing the oil out instead of just moving the pushrod.

[Arquemann]

How freely did the lifters move in the bores? If they didn't slide in easily that might be it. If they fall in there like a hot dog in a hallway thats not good either. The oil feed is a drilling that runs through the length of the lifter galley with a hole roughly mid-way up the hole. There is a necked down area in the middle of the lifter where it actually gets oil in, and whatever isn't required for the lifter itself flows around to the next hole down. if the bores are worn out or the lifters are undersized, instead of pumping oil through each lifter it will just piss out around the lifter and some won't pump up correctly.


if they sit real tight it may be binding a bit and forcing the oil out instead of just moving the pushrod.

They sit very nicely in their bores, and seemed to move appropriately when oiled up. When I had it apart again, I inspected all the lifters and rollers, no marring or scoring on the sides of the lifters, some tiny marks of debris on a couple rollers.
Same thing pre-rebuild, the original flat tappet lifters had barely any wear marks on the sides and the bores looked good and clean, so they weren't even touched up.