Engine Knock

[Kjay]

Recently purchased a 1978 fiat spider. Had to replace both condensers, broken rotor, replaced bad fuel pump with an electric pump and changed oil, had gas in it from bad fuel pump. Once that was done it started right up. Idled smooth and quiet. Then knocks like crazy at rpm over 2000. Checked timing belt and all marks line up at TDC. Is there anything else to check before I pull the engine.

[18Fiatsandcounting]

I responded to your post under "Introductions", but here it is again.

How about the pulley for the auxiliary shaft? On some engines if not timed right, the lobe on the auxiliary shaft for the mechanical fuel pump (even if replaced by an electric) can strike the #2 connecting rod.

With the engine at TDC and both cam pulleys lined up, the auxiliary shaft pulley should have its timing mark at about the 1 o'clock position as you view it from the front. Kinda lined up with the pivot bolt for the timing belt tensioner bracket (the pivot bolt that the spring rides on).

If that's not the issue, then yes, it could be something internal to the engine, especially if the engine was run for a while with gas in the oil.

-Bryan

[Kjay]

I responded to your post under "Introductions", but here it is again.

How about the pulley for the auxiliary shaft? On some engines if not timed right, the lobe on the auxiliary shaft for the mechanical fuel pump (even if replaced by an electric) can strike the #2 connecting rod.

With the engine at TDC and both cam pulleys lined up, the auxiliary shaft pulley should have its timing mark at about the 1 o'clock position as you view it from the front. Kinda lined up with the pivot bolt for the timing belt tensioner bracket (the pivot bolt that the spring rides on).

If that's not the issue, then yes, it could be something internal to the engine, especially if the engine was run for a while with gas in the oil.

-Bryan

I checked auxiliary pulley,timed correctly. I think probably a rod knocking. Was hoping someone had some ideas I haven’t tried.

[18Fiatsandcounting]

I checked auxiliary pulley,timed correctly. I think probably a rod knocking. Was hoping someone had some ideas I haven’t tried.

Two thoughts:
1. You could try a thicker engine oil and see if that reduces the noise. Straight 40 weight or maybe 20W-50 or the like. It doesn't fix the problem, but it might help for a while.

2. Sometimes you can "feel" the looseness in the rod bearings. Remove all 4 sparkplugs. Rotate the engine by hand until the #1 piston is starting to go down. Then insert a socket extension or long metal bar or the like into the spark plug hole, on top of the piston, and push on it with your palm. If the piston "clicks" downward a bit, any movement at all, you've got a bad connecting rod bearing*. If #1 appears OK, repeat on the other cylinders to see if you feel any looseness.

*The knock could be in the wrist pins, but let's not go there for now.

-Bryan

[Kjay]

I checked auxiliary pulley,timed correctly. I think probably a rod knocking. Was hoping someone had some ideas I haven’t tried.

Two thoughts:
1. You could try a thicker engine oil and see if that reduces the noise. Straight 40 weight or maybe 20W-50 or the like. It doesn't fix the problem, but it might help for a while.

2. Sometimes you can "feel" the looseness in the rod bearings. Remove all 4 sparkplugs. Rotate the engine by hand until the #1 piston is starting to go down. Then insert a socket extension or long metal bar or the like into the spark plug hole, on top of the piston, and push on it with your palm. If the piston "clicks" downward a bit, any movement at all, you've got a bad connecting rod bearing*. If #1 appears OK, repeat on the other cylinders to see if you feel any looseness.

*The knock could be in the wrist pins, but let's not go there for now.

-Bryan

Yes have 5w30 in it now with a pint of STP. Could add another stp oil treatment. I have thought of using that method to check for loose rod. I saw in my Chilton manual that on timing belt it shows the auxiliary pulley dowel pin in a 9:30 position. My aux pulley has 2 timing marks on it. Big mark is a couple teeth from dowel pin. This is how engine is currently timed. If I were to use the smaller timing mark that would put the aux dowel in 9:30 position as in the Chilton manual. Beside the Chilton manual everything I read online says go by timing mark close to dowel pin. Maybe worth a try. Crank it slow by hand a couple rounds to be sure it doesn’t hit anything.

[redcars]

10w40 is what fiat recommends. I like 15w40. 5w30 is way too light for an engine from the 60's.

[18Fiatsandcounting]

I saw in my Chilton manual that on timing belt it shows the auxiliary pulley dowel pin in a 9:30 position. My aux pulley has 2 timing marks on it. Big mark is a couple teeth from dowel pin. This is how engine is currently timed.

Hmmmm... Not sure I'm following you here. The auxiliary shaft pulley should have a timing "hole" just like the camshaft pulleys. In fact, I think the auxiliary cam pulley is the same part as the exhaust camshaft pulley. Ignore where the dowel pin is. The auxiliary cam pulley should have a small hole just like like the exhaust cam pulley, and like the exhaust cam pulley, that hole on the aux. pulley should be at the 1 o'clock position when the engine is at TDC and the cam pulleys are lined up with their pointer bracket.

Is that what you've got?

Not saying this is an issue, but just trying to eliminate possibilities.

-Bryan

[Nut124]

If it were the aux shaft lobe hitting the crank/rod, would that not happen regardless of rpm. Should hear at idle just the same?

Knocks at over 2000? Like detonation knock? Did you check ignition timing at various rpms? If not, I would do that. Spark way advanced can sound very bad, like a major mechanical problem.

If it's a bad bearing, I doubt that oil viscosity or additives will fix it. Then again, bottom end bearing problems are not common in these engines.

[Kjay]

If it were the aux shaft lobe hitting the crank/rod, would that not happen regardless of rpm. Should hear at idle just the same?

Knocks at over 2000? Like detonation knock? Did you check ignition timing at various rpms? If not, I would do that. Spark way advanced can sound very bad, like a major mechanical problem.

If it's a bad bearing, I doubt that oil viscosity or additives will fix it. Then again, bottom end bearing problems are not common in these engines.

Ok tried setting to other timing mark. Hit solid before making a full revolution. So reset timing. Ran engine and advanced and retarded timing still knocking. Ran compression test all cylinders between 120-130. So now going to pull oil pan and see what knocking. Probably a bad rod bearing. Thanks for all the useful information.

[Kjay]

If it were the aux shaft lobe hitting the crank/rod, would that not happen regardless of rpm. Should hear at idle just the same?

Knocks at over 2000? Like detonation knock? Did you check ignition timing at various rpms? If not, I would do that. Spark way advanced can sound very bad, like a major mechanical problem.

If it's a bad bearing, I doubt that oil viscosity or additives will fix it. Then again, bottom end bearing problems are not common in these engines.

Ok tried setting to other timing mark. Hit solid before making a full revolution. So reset timing. Ran engine and advanced and retarded timing still knocking. Ran compression test all cylinders between 120-130. So now going to pull oil pan and see what knocking. Probably a bad rod bearing. Thanks for all the useful information.

Got the oil pan off. What a pain to drop the oil pump. That back 13mm bolt was a real fight to remove.. Found my knock, spun bearing on # 1 cylinder. I guess I’ll be pricing parts and a cost for a crank or machine work. Haven’t pulled any other bearings yet to see how everything else looks.

[18Fiatsandcounting]

Main bearing or connecting rod bearing? Do you have any idea how long the engine was run with gas in the oil?

I'm just curious what else you find out.

-Bryan

[Kjay]

Main bearing or connecting rod bearing? Do you have any idea how long the engine was run with gas in the oil?

I'm just curious what else you find out.

-Bryan

It be later next week before I can work on it. So haven’t removed any other bearing caps. When I purchased the car it had fresh oil change and oil had a slightly gassy smell. Once I got fire to plugs I was putting 2 cycle boat gas down carb to start. Unsure how long since it last ran.Probably cranked it a lot before I realized that old wire to points was bad and spark was intermittent. So checked oil then and saw oil was about a quart over full and had real strong gas smell. Changed oil. Repaired points wire took fuel line to fuel pump off. This time started on 2 cycle gas . Replaced mechanical fuel pump with electric. Car started and idled smoothly. When rpm was over 2000 heard a rattling knocking noise. I now believe PO probably knew of the knock. After he let the car sit for awhile decided to sell. As he didn’t want to mess with it. He told me when I bought it that was hard to start, but would run if you poured gas down carb. Guess I’ll be borrowing my brothers cherry picker and pulling the motor. Yes / no pull trans and motor together.

[18Fiatsandcounting]

Yes / no pull trans and motor together.

There's no right or wrong answer; some do it one way and some do it another. My method is to remove the cylinder head, then separate the engine from the bellhousing (and motor mounts), then slide the engine forward and out. Advantages of this method are less weight to deal with, and with the head off, the two top engine-to-bellhousing bolts are easier to remove.

Whichever way you go, remove the radiator first. Gives you more room and avoids potential damage as the engine comes out.

-Bryan

[Kjay]

Yes / no pull trans and motor together.

There's no right or wrong answer; some do it one way and some do it another. My method is to remove the cylinder head, then separate the engine from the bellhousing (and motor mounts), then slide the engine forward and out. Advantages of this method are less weight to deal with, and with the head off, the two top engine-to-bellhousing bolts are easier to remove.

Whichever way you go, remove the radiator first. Gives you more room and avoids potential damage as the engine comes out.

-Bryan

Thanks for your input. I may pull engine your way but install engine and trans together. Since engine will be refreshed going to get trans out clean it up. Give it a new clutch pressure plate and throwout. Brother is encouraging me to replace clutch cable as well. Something I learned today. Gas wasn’t in the crankcase from fuel pump, was leaking past needle and seat. With car closed in garage I smelled gas. Took off gas cap whoosh, fuel tank was really pressured up. Not sure why so much pressure in the gas tank.

[redcars]

Above the rear axle there is a vent valve that gets plugged up over time. It can be cleaned so as to let the tank vent.