warped cylinder head, damaged piston l300

ontheebrink · Post by **ontheebrink** » Thu Jul 19, 2018 9:46 am

I had a glow plug tip fall into the motor and damage a piston. The mechanic removed the pieces replaced the cylinder head gasket and bolts and now it gets air in the coolant. He told me the piston is slightly damaged and the head is warped. He also said if I get the head machined it will cause the piston to no longer work due to pressure and it being loose. Stuck between a rock and a hard place.

It runs now and doesn't overheat so I'm in no rush but I am in need of a rebuild or used motor. I don't think any mechanics around me will bother with a rebuild. Any recommendations on where to get a motor? Could he be wrong and this could be fixed easy?

Post by **Growlerbearnz** » Thu Jul 19, 2018 1:37 pm

Slightly damaged pistons from a failed glow plug are common- as long as the edge of the piston (where it meets the cylinder wall) isn't chipped, the cylinder isn't scored, and its compression figures are about the same as the other pistons, it's ok.

Do you have any photos of the damaged piston? Here's the damaged piston from my old engine- note the dings and dents. It had no issues at all.

: piston.JPG (230.14 KiB) Viewed 3957 times

You can only measure a warped head while it's removed from the engine. Is your mechanic really saying he measured the head, found it to be warped, but reinstalled it anyway, and now it's leaking? Because that sounds like a very silly thing to admit to.

I think he's making it up because he doesn't know why it's leaking. 4D56 heads don't warp often, but they do crack. When the head comes off again, look for a crack between the valve seats or precombustion chamber. You might need to have the head crack tested, as the cracks can be subtle when the engine's cold.

A new cylinder head isn't expensive (relative to a new engine, at least), but make sure you get the correct one; recessed or protruding valves. Check the Technical Reference Library for a guide on knowing the difference.

It's not a great idea to drive with a cracked head. The cracks tend to get larger, and though it's not overheating now, it will soon. There's also the slight risk a valve seat could drop out, which *will* write your engine off.

ontheebrink · Post by **ontheebrink** » Thu Jul 19, 2018 4:00 pm

I doubt he measured it. It started out fine after the repair for a week or two then it started bubbling in the overflow. I took it back and he claimed he didn't tighten the bolts enough. That worked for a bit and now it's bubbling again, I took it back, he checked the bolts and said the head is probably warped.

I didn't have this issue before the repair so i don't think it's cracked. It hasn't overheated either. I am really wondering if he installed the gasket wrong or used the wrong torque measurements or air is getting into the system from somewhere else.

Post by **Growlerbearnz** » Fri Jul 20, 2018 2:21 pm

If he forgot to tighten one (or more) bolts, used the wrong torque, or tightened the bolts in the wrong order the new head gasket might not have sealed. (That would be a nice easy thing to repair). Did he have a printout of the workshop manual?

I still think it unlikely that the head is warped unless a bunch of bolts were left loose- it takes a serious overheat to warp a 4D56 head. They'll usually crack before they warp.

[rant]The kind of mechanic who doesn't check a head for straightness or double-check the bolts for torque also doesn't sound like the kind of mechanic who degreases the head and block properly, or checks the chamfer in the bolt holes, or notices a dozen other little things that would cause a head gasket not to seal properly. [/rant]

ontheebrink · Post by **ontheebrink** » Fri Jul 20, 2018 2:39 pm

I doubt he has a workshop manual.

Would I need to replace the gasket or can I re-torque the bolts? If i need to replace the gasket should I replace the bolts as well?

Post by **Growlerbearnz** » Sat Jul 21, 2018 12:20 am

If there's air getting into the coolant, you need to at least replace the head gasket. If the gasket hasn't sealaed, for whatever reason, tightening the head bolts won't fix it. *Overtightening* the head bolts is asking for trouble. While the head is off you should check it for straightness and for cracks. You don't need to replace the bolts unless they're corroded or have been overtightened, but it might be safest to order new bolts at the same time as the head gasket.

Download the workshop manual and read both the quick "replacing the head gasket" section, and the more comprehensive "rebuilding the engine” chapter. It's not actually rocket surgery, and following the workshop manual eases the learning curve.

ontheebrink · Post by **ontheebrink** » Fri Jul 27, 2018 3:09 pm

Ok, thanks for the advice. I'll give it a shot. Anyplace in particular I should check for cracks?

I'm going to check the compression of the pistons before hand. Will a bad gasket cause any issues while measuring or will I get an even reading across all four if they are good. It seems to only really boil when the engine is warm. When cold it's very slight.

Post by **Growlerbearnz** » Sat Jul 28, 2018 5:46 pm

Compression results: it's hard to predict if a slightly blown gasket or crack will make any difference. Only one way to find out. If they're all the same, the pistons are definitely ok. If one is low, it might be a crack or it might be the piston- but at least when you take the head off you know which cylinder to focus on.

Look for a crack between the valve seats or precombustion chamber and seats. You might need to clean the head with rags and solvent. If there's nothing obvious, it's a good idea to have it crack tested.