Flat tappet cam failure

racer5252

Member
When I started this project I thought it was a simple fix, hoping it was only a bad rocker arm, then thought maybe it was a lifter etc. etc., now I have it tore down to complete bare block after checking a few bearings and seeing something went through it.
After seeing how much damage was done it’s a no brainer to convert to a roller cam set up.
A few questions I have is about the block, the two center main cap oil holes have been chamfered, not sure if they were drilled bigger or for what reason. I can’t seem to find any write ups about prepping the block or what are some good mods to do to it. Also how do I tell if this is the correct crankshaft.
 

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750H.P.V6

Brutal 6 Racing
It looks like the oil feed holes to the bearings and the bearing shells themselves have both been modified. It does appear to be the correct crankshaft. Have you taken a measurement of the crank journals to see what size they are now?

Neal
 

racer5252

Member
It looks like the oil feed holes to the bearings and the bearing shells themselves have both been modified. It does appear to be the correct crankshaft. Have you taken a measurement of the crank journals to see what size they are now?

Neal
I haven’t measured yet but I know they are still standard. Hopefully just a polish job.
 

Chuck Leeper

Toxic old bastard
Staff member
Any trick to fix that besides billet caps and a line bore? More torque?
A line bore/hone would be one way. New caps, line bore is another.
What does the parting face on the caps look like?
Were the caps loose in the register, when you took it apart?
Could well be that the tune up contributed to the issue.
I'm w/ Neal, on the crank.. It's not going to polish out.
From the looks of the thrust brg, the crank thrust is also damaged, and would be an issue.
LOTS of 'dirt" went thru this engine.
Neal also mentioned the turbo. You can be certain the brg is also toast.
If the engine oil cooler is still working, it's toast, also. Either bypass it w/ an external, or replace the one in the rad.
Add the oil pump to the list.
 

750H.P.V6

Brutal 6 Racing
A line bore/hone would be one way. New caps, line bore is another.
What does the parting face on the caps look like?
Were the caps loose in the register, when you took it apart?
Could well be that the tune up contributed to the issue.
I'm w/ Neal, on the crank.. It's not going to polish out.
From the looks of the thrust brg, the crank thrust is also damaged, and would be an issue.
LOTS of 'dirt" went thru this engine.
Neal also mentioned the turbo. You can be certain the brg is also toast.
If the engine oil cooler is still working, it's toast, also. Either bypass it w/ an external, or replace the one in the rad.
Add the oil pump to the list.

+ 1 to what Chuck said about the engine oil cooler. You either need to get a new radiator or run an external cooler. It can't be cleaned, if you rebuild the engine and reconnect the oil lines to the existing oil cooler you'll get to revisit all this same heartache again.

Neal
 

racer5252

Member
A line bore/hone would be one way. New caps, line bore is another.
What does the parting face on the caps look like?
Were the caps loose in the register, when you took it apart?
Could well be that the tune up contributed to the issue.
I'm w/ Neal, on the crank.. It's not going to polish out.
From the looks of the thrust brg, the crank thrust is also damaged, and would be an issue.
LOTS of 'dirt" went thru this engine.
Neal also mentioned the turbo. You can be certain the brg is also toast.
If the engine oil cooler is still working, it's toast, also. Either bypass it w/ an external, or replace the one in the rad.
Add the oil pump to the list.
I did notice the two center main caps didn’t seem as tight as they should have been.
Not sure what do you mean by the tuneup could have contributed to the issues.
Would have all the dirt that went through the engine caused the thrust bearing issue or is that a totally different issue?I will definitely be looking for a new radiator and getting the turbo replaced or rebuilt.
 

Chuck Leeper

Toxic old bastard
Staff member
Would have all the dirt that went through the engine caused the thrust bearing issue or is that a totally different issue?
Looks like the dirt got the brg and crank surface. It could have been aggravated by high loads on the brg, by brake stalling the converter. When that's done, the converter is forced forward, in turn, pushing the crank forward, into the brg.
Does the car have the original trans?
 

turbodave231

Moderator
The crank is definitely a turbo/4.1 version. You can tell by the recessed areas on either side of the journal (they are called "rolled fillets")

Don't send the crank to just anybody. You'll end up with too much bearing clearance. Polishing a crank will only put you in the wrong direction .
Setting one of these Buick V6's up with too much bearing clearance is one of the biggest mistake I see backyard builders make. Some engine builders who are used to setting clearances in larger V8's don't understand the tight clearances needed in these engines.


In my professional opinion, the best way to fix your situation:
You'll need a dial bore gage and decent mike that reads to a ten thousandth .0001"
Measure the journals to see what size they are currently
Determine the bearing undersize needed.
Buy the new bearings
Install and torque the bearings in the block/rods
Measure the new bearings
Calculate your journal size needed to achieve the desired oil clearance
Tell the crank grinder exactly what sizes he has to hit with the grinder.

Chuck and Neal: Good to see the "old timers" posting on the board. Hope you guys are well!
 

earlbrown

runs with scissors
A few questions I have is about the block, the two center main cap oil holes have been chamfered, not sure if they were drilled bigger or for what reason. I can’t seem to find any write ups about prepping the block or what are some good mods to do to it.

They've defiantly been drilled. That heavy chamfer was a bad idea. It exposes the bottom of the bearing to pressurized oil. The last thing you want is to lube the press fit that's supposed to keep the bearing from spinning.

Make sure to match port the new bearings to those holes. So the oil can get in the hydrodynamic wedge where it belongs.
 

racer5252

Member
The crank is definitely a turbo/4.1 version. You can tell by the recessed areas on either side of the journal (they are called "rolled fillets")

Don't send the crank to just anybody. You'll end up with too much bearing clearance. Polishing a crank will only put you in the wrong direction .
Setting one of these Buick V6's up with too much bearing clearance is one of the biggest mistake I see backyard builders make. Some engine builders who are used to setting clearances in larger V8's don't understand the tight clearances needed in these engines.


In my professional opinion, the best way to fix your situation:
You'll need a dial bore gage and decent mike that reads to a ten thousandth .0001"
Measure the journals to see what size they are currently
Determine the bearing undersize needed.
Buy the new bearings
Install and torque the bearings in the block/rods
Measure the new bearings
Calculate your journal size needed to achieve the desired oil clearance
Tell the crank grinder exactly what sizes he has to hit with the grinder.

Chuck and Neal: Good to see the "old timers" posting on the board. Hope you guys are well!
I just ordered new .010 under King bearings for the crank and rods. I’m going to shoot for .0015 to .002 . I’m new at this so all this info is great. Now I have to find a machine shop that can do it.
 

racer5252

Member
They've defiantly been drilled. That heavy chamfer was a bad idea. It exposes the bottom of the bearing to pressurized oil. The last thing you want is to lube the press fit that's supposed to keep the bearing from spinning.

Make sure to match port the new bearings to those holes. So the oil can get in the hydrodynamic wedge where it belongs.
Should I try and chamfer the backside of the bearing?
 

Jerryl

Tall Unvaccinated Chinese Guy
The crank is definitely a turbo/4.1 version. You can tell by the recessed areas on either side of the journal (they are called "rolled fillets")

Don't send the crank to just anybody. You'll end up with too much bearing clearance. Polishing a crank will only put you in the wrong direction .
Setting one of these Buick V6's up with too much bearing clearance is one of the biggest mistake I see backyard builders make. Some engine builders who are used to setting clearances in larger V8's don't understand the tight clearances needed in these engines.


In my professional opinion, the best way to fix your situation:
You'll need a dial bore gage and decent mike that reads to a ten thousandth .0001"
Measure the journals to see what size they are currently
Determine the bearing undersize needed.
Buy the new bearings
Install and torque the bearings in the block/rods
Measure the new bearings
Calculate your journal size needed to achieve the desired oil clearance
Tell the crank grinder exactly what sizes he has to hit with the grinder.

Chuck and Neal: Good to see the "old timers" posting on the board. Hope you guys are well!
THIS!
 

earlbrown

runs with scissors
I just ordered new .010 under King bearings for the crank and rods. I’m going to shoot for .0015 to .002 . I’m new at this so all this info is great. Now I have to find a machine shop that can do it.

That was premature. First you need to polish your crank and get a measurement with an accurate set of mics. THEN you can make a game plan on bearings. If you have to have the crank turned .020, those bearings won't be of any use to you.

Should I try and chamfer the backside of the bearing?

NO!
 

racer5252

Member
Well I guess worst case I’ll have to buy new .020 under bearings. I measured them without polishing and thought I should be fine with .010 under. My thinking was why pay to have someone polish it just to turn around and turn it down. We’ll see, I’m still learning.
Is 3/8” hole the biggest I should go for the 2 center main bearings? That’s what it was before.
 

racer5252

Member
A line bore/hone would be one way. New caps, line bore is another.
What does the parting face on the caps look like?
Were the caps loose in the register, when you took it apart?
Could well be that the tune up contributed to the issue.
I'm w/ Neal, on the crank.. It's not going to polish out.
From the looks of the thrust brg, the crank thrust is also damaged, and would be an issue.
LOTS of 'dirt" went thru this engine.
Neal also mentioned the turbo. You can be certain the brg is also toast.
If the engine oil cooler is still working, it's toast, also. Either bypass it w/ an external, or replace the one in the rad.
Add the oil pump to the list.
I just got my new billet main caps so I’m ready to take the block and crank to the machine shop. You mentioned that by the looks of the thrust bearing that the crank thrust could also be damaged, is there a way to check it? Also I want to verify that the bearing clearance for the rods and mains need to be between . 0015 and .0023
 
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