• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

My very bad day: shattered valve, gouged piston

Shinchan

Member
Joined
Jun 28, 2018
Location
Lafayette, CO
Well, my Megasquirt/B20 project has come to a grinding halt. One of my exhaust valves sheared off at the lower retaining groove (I'm guessing it was defective, there is no sign of a broken valve guide) and dropped down into the block. Piston shattered the valve, but not before it made a pretty sizeable gouge in the piston. I haven't even assessed the head yet.

I'm trying to figure out next steps. Once I clean out the debris and carbon, I can get a good look at the piston. The block only has 5k on the rebuild, so I'm pretty frustrated.

So the question is, run it or replace the piston? I just put the engine in, so I'd rather not pull it. Is it possible to swap a piston from underneath, or am I just going to need to bite the bullet and pull the engine?

126486539_3530956743654449_2828172364542492287_o.jpg
 
Probably not a good idea. Better to swap it, rather than risk having it come apart later. You can replace pistons with the engine in the car, but generally speaking, it's going to be less work to pull the motor. It's not particularly easy to pull the oil pan with the motor in the car.
 
I might try lifting the engine enough to get the oil pan out and then setting it back down to do the work. I reeeeeealy don't want to pull the engine.

Probably not a good idea. Better to swap it, rather than risk having it come apart later. You can replace pistons with the engine in the car, but generally speaking, it's going to be less work to pull the motor. It's not particularly easy to pull the oil pan with the motor in the car.
 
Seems like it would be easier to pull the engine and trans all at once. Working under a car on a job like that sounds like a real pain in the a$$. That really sucks, sorry that happened to you OP.
 
Last edited:
Ream the ridge at the top of the cylinder, pull the oil pan (the trickiest part), remove the 2 cap screws at the end of the rod, push the piston out through the top of the block.

At least I'm hoping that it's that simple.

Seems like it would be easier to pull the engine and trans all at once. Working under a car on a job like that sounds like a real pain in the a$$. That really sucks, sorry that happened to you OP.
 
Last edited:
If you don't have an engine hoist and an engine stand, then doing it in the car might be easier.

I've pulled pans a couple of times, always seemed like a PITA. On a 140 I had to drop the front crossmember (while supporting the motor). You need enough clearance to remove all the oil pan bolts, then drop it down far enough to unbolt the oil pump. Then when reassembling, it's highly tricky to ensure you have the oil pump transfer tube seals in place properly when reinstalling the pump to the block while the oil pan sits in the way. Unless you *really* get a lot of room between the motor and crossmember and can fully install the pump, then put the pan on.
 
I have a hoist. The plan was to disconnect the driveshaft and lift the front of the engine while letting the nose of the trans drop down. Hoping this will give me enough clearance to pull the pan. I installed the engine by myself (no help where I'm at plus Covid) but I don't want to have to do that again by myself if I can avoid it.

If you don't have an engine hoist and an engine stand, then doing it in the car might be easier.

I've pulled pans a couple of times, always seemed like a PITA. On a 140 I had to drop the front crossmember (while supporting the motor). You need enough clearance to remove all the oil pan bolts, then drop it down far enough to unbolt the oil pump. Then when reassembling, it's highly tricky to ensure you have the oil pump transfer tube seals in place properly when reinstalling the pump to the block while the oil pan sits in the way. Unless you *really* get a lot of room between the motor and crossmember and can fully install the pump, then put the pan on.
 
The motor generally only tilts back a little before the head hits the firewall, but in our case, with no head on it, might work.

With the head off you're just a few more bolts away from pulling the rest of it out.

I've pulled motors with the trans on, and without. It's pretty much a wash in terms of which is easier. With an OD trans, it's long enough that you generally need to lift the front of the car up to give it room. Just take the radiator out, no need to remove anything else.

Do you have a load leveler? That makes installing motors super easy. Just crank the handle to change the angle of the dangle. Almost feels like cheating.
 
When pulling a red block and transmission I now remove not only the radiator / condenser / intercooler but also everything in front of and on top of it, including the light assembly: remove everything above the bumper and between the front fenders.
 
Ouch! I had the same thing happen on my Tundra this summer. The valve just fell off the stem 18k miles after I rebuilt the motor. The reason I had to rebuild was because on drivers side bank, the valves hit pistons due to timing belt slip. There was no apparent damage to the passenger side head, so I reused it after inspection. Turns out it must have had a micro crack in the valve stem.

At least your rod is still ok. Mine was bent so the piston top was about a mm lower at TDC than the other cylinders.

<a href="https://imgbox.com/g3meZFOE" target="_blank"><img src="https://images2.imgbox.com/7a/68/g3meZFOE_o.jpeg" style="width:600px;" alt="image host"/></a>
 
T5 trans, which is a little beefier than the original trans and a shade longer than the M41

The motor generally only tilts back a little before the head hits the firewall, but in our case, with no head on it, might work.

With the head off you're just a few more bolts away from pulling the rest of it out.

I've pulled motors with the trans on, and without. It's pretty much a wash in terms of which is easier. With an OD trans, it's long enough that you generally need to lift the front of the car up to give it room. Just take the radiator out, no need to remove anything else.

Do you have a load leveler? That makes installing motors super easy. Just crank the handle to change the angle of the dangle. Almost feels like cheating.
 
I had a T5 on the 16V motor. I'm not sure if I ever installed that with a complete 16V motor with the T5 bolted on. The 16V motor has a lot less room to tilt (at least in a 240). And the T5 was so easy to unbolt - leave the bellhousing on and just take 4 bolts off and slide the trans back.
 
This sad story again illustrates why you should replace exhaust valves when performing an overhaul. From my experience, it is rare to see an intake valve fail but the exhaust sides are the typical failure point due to the thermal stress on them.

I also pulled a redblock oil pan in situ in my 940; a PITA it was for sure..... and then I found out the rear thrust bearing was toast due to an incorrect AW71 swap, and ended up pulling the engine to replace it!

For the value of my time, I'm pulling the whole shebang.
 
The entire valvetrain was brand new including valves, guides, seals, etc.
I'm guessing the valve was defective from manufacturing.

This sad story again illustrates why you should replace exhaust valves when performing an overhaul. From my experience, it is rare to see an intake valve fail but the exhaust sides are the typical failure point due to the thermal stress on them.

I also pulled a redblock oil pan in situ in my 940; a PITA it was for sure..... and then I found out the rear thrust bearing was toast due to an incorrect AW71 swap, and ended up pulling the engine to replace it!

For the value of my time, I'm pulling the whole shebang.
 
Well, I guess the head could be worse. The broken valve slammed into the intake valve and it ended up 'S'-shaped. Both valve guides broken. Valve seats have some damage that I'm not sure can be cleaned up without going to oversized valves. Overall a pretty ****ty week...

<img src="https://i.ibb.co/1ZsjHLq/IMG-7678.jpg" alt="IMG-7678" border="0">
 
Probably not a good idea. Better to swap it, rather than risk having it come apart later. You can replace pistons with the engine in the car, but generally speaking, it's going to be less work to pull the motor. It's not particularly easy to pull the oil pan with the motor in the car.

You mean, an in-frame rebuild? Now we're talking.
 
Ream the ridge at the top of the cylinder, pull the oil pan (the trickiest part), remove the 2 cap screws at the end of the rod, push the piston out through the top of the block.

At least I'm hoping that it's that simple.
I'll add my 2 cents here:

I'd bet that you could get away with just putting a head on it. I don't think I would, but you could.

Having said that, if this is a performance engine, I would be concerned about a hot spot, from a high spot along the edge of the gouge, causing detonation. It probably wouldn't, especially if you cleaned up the top of the piston aggressively. But, knowing that it could be detonating in that one cylinder without me even being able to hear it, would be enough to have me pull the block and swap the piston if it was my car.


If the block only has 5k on it since the rebuild, I would be surprised that you'd have a ridge. Are you sure that you have a ridge?
 
It doesn't have a ridge, so I'll just be popping the piston out tomorrow.

New piston is on the way, I'm not taking any chances on this piston, it could be cracked for all I know.

I'll add my 2 cents here:

I'd bet that you could get away with just putting a head on it. I don't think I would, but you could.

Having said that, if this is a performance engine, I would be concerned about a hot spot, from a high spot along the edge of the gouge, causing detonation. It probably wouldn't, especially if you cleaned up the top of the piston aggressively. But, knowing that it could be detonating in that one cylinder without me even being able to hear it, would be enough to have me pull the block and swap the piston if it was my car.


If the block only has 5k on it since the rebuild, I would be surprised that you'd have a ridge. Are you sure that you have a ridge?
 
Back
Top