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Discussion Starter #1
Finally have the car on the road after three months fighting many problems with the rebuild.

There is a vibration in the engine that was not there before the rebuild.

If I put the piston rods in backwards could this be the cause? Is this even possible?
 

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I think before jumping to potential causes it would be better to describe the vibration, i.e. what revs?, does what gear the transmission in make a difference?, does it change if the engine is cold or hot?

Pete
 

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Yes, is it related to engine rpm or instead road speed? Does it change whether sitting still or driving?
If the rods are in backwards you shouldn't have been able to turn it over, they bind. Although I took apart a 750 engine once with the rods backwards and all the pistons were worn sideways.
Andrew
 

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Discussion Starter #4
Yes, is it related to engine rpm or instead road speed? Does it change whether sitting still or driving?
If the rods are in backwards you shouldn't have been able to turn it over, they bind. Although I took apart a 750 engine once with the rods backwards and all the pistons were worn sideways.
Andrew
The engine vibrates both warm and cold . With the clutch in on the highway you can still feel the vibrations . The vibrations get stronger as the rpms increase. Now that i think about it , the engine was harder to turn by hand as the pistons approached the top .
I thought this was from the compression... maybe not.😭

I will be able to pull the lower oil pan in a few days and get a look at the piston rods on #1 and #2. Then I’ll know if this is the problem. I will post what I find here .
Larry
 

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If the vibration is the same at the same rpm in any gear, it's coming from the engine. What did you do re engine mounts and trans mount?
Andrew
 

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If I put the piston rods in backwards could this be the cause? Is this even possible?
The offsets of the rods do require that they be installed in a particular way. Your manual (you do have a manual?) will show this. But as Andrew wrote, if one or more rods were installed incorrectly, the engine would bind as you tried to rotate it.

Tell us what else you did as part of the rebuild: new pistons? new clutch? were the rotating parts balanced before assembly? Not balancing new parts - or installing old parts in different locations - could be the source of your problem.
 

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In general, Alfa's standard balancing and assembly were good enough for any normal use engine. But if you have a mix n match of parts, etc. it could be unbalanced. But factory balance of crank and flywheel are done separately and normally can be assembled in any orientation and work. Unless they were redone by someone else.
Anyone local who can help give an informed opinion?
Andrew
 

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Richard Jemison
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If you can feel the vibration with the car out of gear, have someone run the car at different RPMs while you feel the various areas of the engine, clutch, & trans. Best to do this on a lift. But not one that lets the rear axle droop if you are thinking it might be the drive shaft.
Look also for any contact of any part of the driveline or headers to the chassis.
 

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Discussion Starter #9
If you can feel the vibration with the car out of gear, have someone run the car at different RPMs while you feel the various areas of the engine, clutch, & trans. Best to do this on a lift. But not one that lets the rear axle droop if you are thinking it might be the drive shaft.
Look also for any contact of any part of the driveline or headers to the chassis.
Found the problem!!!! I installed at least one piston rod in the wrong orientation. Pulled the lower pan and looked at pistons#1and 2. They were both facing the same way, so at least one was installed incorrectly.
I was very careful when I installed them.. I am still having trouble seeing which way they are offset which caused the mistake.
Now , I think the offset is in the direction opposite the big lip on the piston rod nig side . Below is a photo I found on another post in this forum . It shows the big lip facing the middle between #1 and #2 and facing the middle between #3and #4 .
I think I got confused and probably put the large lip facing out on #1 and # 4 which is incorrect.
Yes the engine is running . Actually very well... just vibrating .. fixing the orientation to match the photo I believe will solve the vibration proplem
1681570
 

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Discussion Starter #10
Found the problem!!!! I installed at least one piston rod in the wrong orientation. Pulled the lower pan and looked at pistons#1and 2. They were both facing the same way, so at least one was installed incorrectly.
I was very careful when I installed them.. I am still having trouble seeing which way they are offset which caused the mistake.
Now , I think the offset is in the direction opposite the big lip on the piston rod nig side . Below is a photo I found on another post in this forum . It shows the big lip facing the middle between #1 and #2 and facing the middle between #3and #4 .
I think I got confused and probably put the large lip facing out on #1 and # 4 which is incorrect.
Yes the engine is running . Actually very well... just vibrating .. fixing the orientation to match the photo I believe will solve the vibration proplem
View attachment 1681570
I went back and looked at the photos I took today with the oil pan off. I am not convinced that both visible piston rods are facing the same direction. Just getting more confused. Tomorrow I will turn the engine by hand and see if it is binding more in any portion of the rotation .This won’t tell me for sure if the puston rods are installed wrong, but it will tell me if something is going on in the engine .
 

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Not sure why this would cause a vibration, but yes you need to get this right

Pete
 
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Richard Jemison
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In your first pic all rods are correctly positioned.
Rods 1 and 4 face outward, 2 and 3 face the middle(towards each other( as you show..
 

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Discussion Starter #13
In your first pic all rods are correctly positioned.
Rods 1 and 4 face outward, 2 and 3 face the middle(towards each other( as you show..
Unfortunately, thst is not my picture, but a photo from another post showing the correct orientation.
I was able to see into the first two pistons from below. There was clearance on both sides of the piston rod where I could see the silver wrist pin.
I spoke to Wes Ingram last night( the spica rebuilder) , he was of the opinion if there was clearance I could see on the wrist pins, then the rods were installed correctly. Can anyone confirm this?

I spoke to the owner of the engine shop which re-did the crank. It was his opinion that the vibration was caused by a balance issue . Either the weight of the piston and rods, or a balance problem on the flywheel/ clutch.

I did have the flywheel resurfaced . the pressure plate and the clutch disk were not changed. Maybe I created the problem here.

He said there was a possibility that there was a problem with the combustion in on of the cylinders. I will check the spark plugs. The engine is running well except for the vibration, so I doubt this is the cause.

Before I put the engine back together, The machine shop measured all the bearing surfaces, and found no problems . The owner told me that the crankshaft was checked for straightness.

Tight bearings,I don’t think would cause a vibration, butI’m not sure. I am not even sure a reversed piston rod would cause a vibration.

The only thing I can think of now is to pull the engine. Check the balance on the flywheel and pressure plate, Then the pistons, and if necessary, finally the crank.

larry
 

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Discussion Starter #14
If the vibration is the same at the same rpm in any gear, it's coming from the engine. What did you do re engine mounts and trans mount?
Andrew
The engine and transmission mounts were not changed for the rebuild. The
 

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the pressure plate and the clutch disk were not changed. Maybe I created the problem here.
Yes, maybe. If the flywheel and pressure plate were balanced together and then assembled in a different orientation, that could throw things off. Each should be balanced separately OR balanced together and marked so they are always assembled the same way.

The only thing I can think of now is to pull the engine. Check the balance on the flywheel and pressure plate, Then the pistons, and if necessary, finally the crank.
Without knowing for sure what is wrong, I don't have a better idea. But don't be surprised if you go though the balancing process and find no issue. Troubleshooting this sort of problem often goes that way.
 

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Discussion Starter #16
I am beginning to think the problem might be in the balance of the flywheel clutch assembly. I did weigh the pistons / piston rods before assembly and they were all within 4 grams of each other.

I plan to pull the engine (again) next week and after marking the orientation of the pressure plate ,bringing the flywheel and clutch assembly to the engine shop to check the balance. If nothing is óbvios, I’ll then remove the head and oil pans , and bring the Pistons/ piston rods to be balanced to 0.5 grams, at the same time I will confirm the orientations of the piston rods from my rebuild, and also confirm all the big end bearing clearances.
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I can’t imagine that that engine vibration could be caused by anything else.
I will post the results here as things progress
Larry
 
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