Knocking motor. What have I broken? (apart from my heart)

I have a 1975 308GT4 project.

The motor was rebuilt by an experienced Ferrari mechanic some time in the last 10 years and never run. I have owned it for the last 6 months and have been gradually finishing off things and getting it ready to run again.

I have had the cam covers off, valve clearances checked, cams out, new cam belts, seals, whatever I came across. I could see the pistons were brand new.

When everything was finally together, I cranked the car with the starter to check I could get oil pressure. It cranked for a while but no pressure. I disconnected the oil cooler line and fed oil directly into the hose and into the cooler. Cranked some more and I eventually had oil flowing. I could hear it, and see fresh oil when I took the oil fill cap off.

I finally started the car on Friday and it started easily and ran beautifully. After a few seconds of running the oil pressure gauge finally registered. I stopped and started it a few times, had it running to check the timing on both distributors, and a slight tune of the carbs. The radiator fans are off the car, so I was watching the temperature and called it a day when the temperature was getting on the high side.

I was so happy. But then ......

Today I started it again, I set up a fan at the front of the car, and was going to do some more tuning of the carbs.

As soon as I started it the engine was knocking. I gave it a few seconds, a few revs, still knocking.
I thought maybe the timing had moved so I ran it long enough to check the timing with a timing light. Timing was still good.

I noticed I didn't have oil pressure, but when I looked under the oil fill cap I could see oil had been moving around (the rear head at least).

I pulled all the plugs, and took off the alternator/water pump belt. When I crank the motor around by hand, there is a tight spot at the same point on every rotation.
I marked the spot on the crank pulley where the tight spot was, and its roughly 90 degrees from my TDC mark, so I am thinking it might be cylinder 5 TDC (in my least favourite head to remove)

I know I have a lot of work ahead of me, but from that description does anyone want to share some thoughts on what I might have done?
Are those symptoms consistent with dropping a valve?

I thought I would start by taking the cams out so all valves should be closed, and doing some pressure tests, or maybe if I get that far in there will be a visual indication as to what is wrong.

Any thoughts?

 

Rod knock happens from oil starvation either caused by your start up procedure or the rebuild was incorrect. When I rebuild a motor I pressurize the oil system including priming oil pumps the best I can depending on what I can access on the different motors. My 1st turn of the key will be plugs out and a couple of 2 sec. pulses. Then I'll start the car and I always see near instant oil pressure. There is no way to know how long you ran without oil, what the 10 year old assembly lube on parts looks like assuming builder used some, what clearances really were, or if there was debris from bad rebuild sucked into an oil hole. If you see a bad bearing that's it. If not I'd be looking everywhere like piston to wall clearance, oil pump all of it.

 

Sorry man.

 

You know where the tight spot is, that makes it a little easier.
Before the cams come out I'd take the valve covers off and check alignment of the cam timing marks and the valve clearances.

I suspect the engine is coming out but I think you should do your best in figuring it out before it is taken apart.

 

Thanks Mr Bob for the reply. Yes there will be a lot of checking.
If someone presented you with an engine that had a tight spot at the same spot on each rotation of the crank, what would you assume the damage is?

It ran beautifully with oil pressure for a few times. Then sat for a day, then had the knock on the next start up.

 

So if the timing marks dont line up anymore, and the mechanical timing is out, I would have bent a valve yeah?

 

Very possibly. Bent valves almost never make noise or cause a tight spot in rotation. Once they are bent out of the way from the 1st contact thats all pretty much over. If you have a tight spot rotating the motor combined with a noise and it is valve related it would more likely be from a broken valve. If during the overhaul either the OE exhaust valves were not replaced or if they were replaced with more OE valves a broken valve is a possibility. Pulling spark plugs will probably tell that story. I have fixed a lot of Ferrari engines with broken valves and never seen a case where the spark plug didn't get smashed. The very 1st Ferrari engine I ever took apart was in 1977 and it was a Lusso with a fresh engine and a broken valve.

 

A borescope that hooks to your phone is helpful too. If the piston has marks on top then it's hitting something. If it is has no marks then it's possible a rod bearing has gone. Have a good look around.

Sorry you're dealing with this. If it's a stock piston, I have a couple good ones floating around I'll donate to your cause.

one like this:
https://www.ebay.com/itm/314383960303?hash=item4932be88ef:gksAAOSwhN9j06eJ&amdata=enc%3AAQAIAAAA4N%2Ffwt2%2BvV99ziA%2FeN8Mu6FbRjVjo7urR%2F6davlh8DIUcAcnv%2BocgwsT34cxZnJhBPfa%2FuuORERRVO3WANuNaESuRX4Owm4VIi2N0awdzet68vKVniHiAW0QrZt1eOHnuY8bGJdn%2FTpIsBBiyUj2aeFm16MatjbkKM8Bcd%2ByRZnAjEofmaRRtQSXQ0AiVUkyzj1fczMmLM0hUYXWkhw37IUFQMayRGGWKjqKIv6Xg%2FQOUySSU094j5fmUPsORy0fo5CYgBSDwda1XOpOTlz8Dva2y27tWocWO9Ru042LDkln%7Ctkp%3ABk9SR5Sysab6YQ

 

Thank you so much for the help.
I pulled all the plugs and none where smashed. I had one where the gap was a bit smaller than the rest which was surprising (thought it may have been knocked in transit as they where taken out and put back in before startup), but that was it.

 

Thank you for your offer, that's really generous. It has been fitted with JE pistons during the rebuild.

 

Good news.

 

Proceed slowly and methodically. Have a look at the other stuff I mentioned.

 

Is it worth restarting it and using a stethoscope ( even a bit of fuel pipe ) to locate the area where the knock is originating.

If we are leaning towards it’s not “ up top “ by the condition of the plugs , and or a e bay phone cheapo borescope reveals no bent valves ?

 

No oil pressure can wipe a main bearing.
Clogging the Main Shaft with babbitt debris.
Reducing oil flow to the wrist pins.
Check cam shafts for debris, flush out the inside the cams, for they are hollow. ( use a coffee filter to catch. )
( note) in the event of a cam belt slipping, a bent valve isn’t going to be deduced by a clean set of plugs.

a beautiful car and a nice project.
good luck,
Go slow.

Edwardo.

 

Yeah, not knowing anything, I'd love to stick a boroscope camera down each spark plug hole and see what the top of the piston looks like and also the cylinder walls and valves. Even a cheap single camera scope would be helpful. I bought one from Amazon for under $40 that has been great. It has an optional 90 degree mirror that can attach on the end. But they have more expensive scopes that have multiple cameras on the end pointing along three axes. You could put one of those down the spark plug hole and very quickly see everything.

That said, knock always makes me think bottom end but without being there and hearing it, hard to say anything helpful.

So many things could go wrong after a rebuild. You might have great oil pressure overall but if it doesn't get to one critical spot, bad news.

 

Maybe just me, but there is no way that I am going to restart a motor that has any unexplained knock.

 

At this point it would be dumb.

 

And how would knowing that effect how you proceed?

 

Did we determine that? News to me. And just how will a cheapo borescope reveal no bent valves?

I want one of those cheap magic tools.

 

Well once that rod finishes sawing its way through the block well know exactly what it is.

 

They come with a reverse mirror .So with plug removed on the suspect cylinder simply insert ( not too deep re clearance of piston ) and turn by hand the engine watching the valves from the inside .Open and close fully .Or not !

 

Not. A bent valve is not always obvious when the head is off or the valve is in your hand. It certainly is not obvious with a cheap bore scope viewed through a mirror.
Measuring valve clearance is far more certain.

But its all BS anyway. When was the last time you heard a bent valve? I have been doing this for 47 years and never heard a bent valve. Just what kind of noise do they make? Help me so I can be smart too.

How long have you been diagnosing broken engines....yesterday?

 

I stand by my post #13 in its entirety.All of it !

Never said anything about “ bent valves “ but you have mentioned them not me .

 

Good. Now we can ignore you as a serious source.

 

I'm with Brian.....time to pull the engine and find out what is wrong with it before it destroys itself. The sooner you find out what is really wrong.....the sooner you get it fixed.