[steve25]

From your picture of the bearing it shows that there is or was a lot of fine grit in that motor and the fact that each bearing near its ends show no ware means that the rod bore is out of round to some degree.

That condition can lead to spun rod bearings and potentially a rod failure which 99 % of the time takes the block out.

How many rod bearings look that way?

Before you take the crank out to look at those bearings check the crank end play and note that down.

[BILL BOWMAN1]

Its a good thing that it didn’t start!!

[chiphead]

Originally Posted by Mikael Nielsen

I have now aligned the crank and the cam as good as possible, and is now trying to turn the piston.

While removing, I noticed the upper rod bearing having some small scratches. Are these okay? Or do I need to replace all of them?
The previously owner replaced them all, but I am not sure if it's damaged.

Picture attached

That is a lot of bearing damage if it only ran for a few minutes. As one of the other guys said, that indicates there was contamination of the oiling system when the engine was built. Check some more bearings for the same condition. Any bearing with that much damage should be replaced. If I saw that in an engine that was removed from the car, I would fully disassemble the engine and clean the block's oiling passages. That level of bearing damage is unacceptable for a motor you want to live a long time.

Also be aware you cannot just turn the rod around to fix the orientation of the piston. The bearing chamfer must face the outside of the rod journal. Usually this means having a machine shop press out the wrist pin and correct the orientation of piston to rod. Is this the only piston that is backwards? The notch or arrow on the top of the piston must face the front of the engine, and the chamfer on the big end of the con rod must face the outside cheek of the rod journal. The prevents the rod bearing from contacting the radius at the journal's edges where the crankshaft journal meets the edge of the crank throw.

Are you in the US or somewhere else? In the US, its fairly easy to find other heads. The 6X-8 heads are very low compression. I would find a set of 5C-4, 5C-9, or 6X-4, or 96 heads to use instead. If you're stuck with the 6X-8, then have them milled about .050" and check intake fitment.

Not a Pontiac but the basics are the same:

https://www.youtube.com/watch?v=F6hQ6W8jobs

[Mikael Nielsen]

Perfect!
I didn't expect this to be a complete rebuild, but here we are I guess 😅.

Tommorow I will take out all of the pistons, to check the bearings and their orientation.
Then also do a check of the crank play and check all of the main bearings.

I am pretty stuck with the X6-8 heads, as parts are difficult to come by in Europe..
The plan is to get the machine shop to remove 0.060 from the heads and remove 0.045 of the intake manifold as per Steves recommendation.

[Stan Weiss]

Originally Posted by Mikael Nielsen

Perfect!
I didn't expect this to be a complete rebuild, but here we are I guess 😅.

Tommorow I will take out all of the pistons, to check the bearings and their orientation.
Then also do a check of the crank play and check all of the main bearings.

I am pretty stuck with the X6-8 heads, as parts are difficult to come by in Europe..
The plan is to get the machine shop to remove 0.060 from the heads and remove 0.045 of the intake manifold as per Steves recommendation.

As I said before.
Measure everything and calculate your current CR.
Measure / Identify what your cam specs are

BEFORE YOU DO ANYTHING TO THE HEAD

Stan

[chiphead]

Originally Posted by Mikael Nielsen

Perfect!
I didn't expect this to be a complete rebuild, but here we are I guess 😅.

Tommorow I will take out all of the pistons, to check the bearings and their orientation.
Then also do a check of the crank play and check all of the main bearings.

I am pretty stuck with the X6-8 heads, as parts are difficult to come by in Europe..
The plan is to get the machine shop to remove 0.060 from the heads and remove 0.045 of the intake manifold as per Steves recommendation.

Post pics of the crankshaft journals. Its possible the bearing damage is due to rough crank journals that were not properly machined the last time the engine was rebuilt. Condition of the cam bearings can help tell the tale. If they are in good shape, the crank was rough. If the cam bearings are all chewed up, then debris in the oil is more likely.

[Mikael Nielsen]

I have now removed all the rod bearings and pistons. It's almost the same on all of them.

I measured the crank play before I removed one of the main bearings. It showed 0.0078 inches.
I have attached a picture of the bearing and crankshaft. I guess I have to order new main bearings also with new bolts..

I could not find any information on the cam, so I measured the height of the intake and exhaust cam to 0.275 inches.

I have calculated the CR value as good as I can to 7.72:1
I have attached a photo of the data I have used.

Thank you everybody.

[Mikael Nielsen]

I can see the pictures were pretty bad. I will take new ones tomorrow. I hope I don't need to machine the crank also.

[Mikael Nielsen]

I made a mistake on the calculation, due to the wrong type of piston I chose. The new value is 7.27:1

So not really better..

[chiphead]

Originally Posted by Mikael Nielsen

I can see the pictures were pretty bad. I will take new ones tomorrow. I hope I don't need to machine the crank also.

That crank absolutely needs to be polished or maybe turned to the next undersize. A quick check is if you can catch/feel your fingernail drag on any of those grooves on the journal, the crank must be machined.

Those journal surfaces are not serviceable as they are. The brown wear mark between the rods bearings indicates long term wear. This crank was not machined properly the last time the engine was built. I would say the bearings are also too tight, but without knowing the condition of the journals beforehand, or knowing if the oil was contaminated, it hard to say why the bearings were moving metal the way they are. The contact patch looks too long on the main bearings, so I suspect the main bolt torques were incorrect. What size are those bearings? Are they marked STD or some undersize on the back side of the shell?

The correct way to figure bearing clearance is to mount new bearings into the main caps and torque them without the crank in place. Measure the internal diameter of the bearing inserts with a dial bore gauge. Use those measurements to determine the exact diameters to machine each crankshaft journal to achieve the desired oil clearance of .0025". That's the way the pros do it. The easy way is to just turn the crank journals to the next undersize, but the actual clearances can be wrong/scattershot doing it that way if the block is out of spec.

Your next job is finding a very good machine shop close to you. Do not order any parts before bringing that crank to a machine shop.

[Mikael Nielsen]

Damn. As I feared.. I will get in touch with the machine shop.

Strange thing is, when I tried to loosen one of the main bearings, it was almost completely loose.
But thank you for the long explanation.

[johnta1]

Pontiac 400 specs are different than what you input.


Here a screenshot of what I would use. (don't know what you actually have)

[steve25]

You mean a main bolt was loose or you mean a bearing was loose such that it was not snapping into place?

Thats a late thin wall block so as posted above do not order any new parts until ,

1) the block passes a mag test, especially the main web area and the main cap bolt holes.

2) the line bore of both the crank and Cam are checked.

[Dragncar]

Originally Posted by Mikael Nielsen

I have now removed all the rod bearings and pistons. It's almost the same on all of them.

I measured the crank play before I removed one of the main bearings. It showed 0.0078 inches.
I have attached a picture of the bearing and crankshaft. I guess I have to order new main bearings also with new bolts..

I could not find any information on the cam, so I measured the height of the intake and exhaust cam to 0.275 inches.

I have calculated the CR value as good as I can to 7.72:1
I have attached a photo of the data I have used.

Thank you everybody.

You are not going to need new main bolts. The old ones, if OEM will be fine.

[steve25]

If you have factory pistons with the chamfer around there perimeter then your compression is less then 8 to 1.

[chiphead]

Originally Posted by steve25

You mean a main bolt was loose or you mean a bearing was loose such that it was not snapping into place?

Thats a late thin wall block so as posted above do not order any new parts until ,

1) the block passes a mag test, especially the main web area and the main cap bolt holes.

2) the line bore of both the crank and Cam are checked.

Steve, he said it was a '73 block, so it should be one of the stronger castings with the thicker webs. Thats good. FYI for OP, the blocks starting in mid year '75 had a lot of cast iron removed from the bulkheads that support the main journals. Thats why the '75-79 blocks that end in '557" are the weak thinwall blocks.

The good news is your '73 is very strong for what you're doing. I would suggest having a shop check the block's main bores for size and distortion. It appears that the last builder had no idea what he was doing, and that could include doing some crazy things to the block or main caps. Checking the housing bores to make sure they are within tolerance of 3.1880 to 3.1890". This is the diameter of the main caps when installed on the block and torqued to spec WITHOUT bearings. This confirms the block will retain the bearing inserts properly and this has a direct impact on bearing to journal oil clearance.

I'm terrified at this point to ask a lot of questions about the pistons or rods. Checking the piston-to-cylinder wall clearance and condition of rod big-ends should be done as well. I would not assume that any of this build could be re-used without proper inspection. I know this is a lot to digest, but I don't want you to spend the time and money just for the engine to fail again because some issue was not found and fixed.

[steve25]

Yes, sorry I forgot the year of his block.

[johnta1]

Here a screenshot of what I would use. (don't know what you actually have)

The stroke should be 3.75 for a 400, was thinking 455.

[Mikael Nielsen]

Alright. I will have the block checked out, and get the crankshaft overhauled.
Strange thing is that the previous owner had the block testet and honed with new pistons and everything. I have attached a picture of the piston installed.
It was the bolt to the main bearings that was loose, and the rest was pretty easy to loosen with very little power.
If the compression will be that low, maybe it's easier to just buy some alu heads? (when I know the rest is OK).

[steve25]

That's a 8 notch aftermarket piston and it's lowering the motors compression even more then stock, and there not that durable if you have tuning problems.

Those Pistons will not survive if the wall clearance is too great and with signs of grit that has gone thru that motor the piston skirts might be worn .

Once again have everything checked out before you go spending money on heads that you might not need.

On aside note if Rods are stock I would plan on replacing them, not rebuilding them.

All your decisions need to be based on how hard it might be to replace that block where you live if a major failure takes place.