Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
Hi, I am hoping for some opinions on the damage and wear I have found on an engine I have stripped down and will be rebuilding. It is a 4U-GSE 2.0 boxer engine turbocharged.
Pistons - Cylinder 3 has severe detonation marks melting the edge of the piston crown, cylinder and combustion chamber. Cylinder 2 has light detonation marks. Scuffs on all piston skirts and cylinder walls.
Piston to bore clearance specified by the piston manufacturer is 3 thou (0.0762mm) the clearances I have measured after strip down are:
Cyl1 - 0.06 Cyl2 - 0.07 Cyl3 - 0.095 Cyl4 - 0.065. (mm)
The map is going to be revisited to sort out the detonation problem.
Also found wear on the main bearings and big end bearings. I haven't measured the clearances yet. I will do that tomorrow. There were also some brief oil pressure drops due to a sticky oil pressure relief valve in the dry sump pump. But I am trying to iron out any issues with the assembly of the engine.
Any advice is appreciated. I will try and upload some pictures shortly.
Thanks in advance.
Unfortunately some of the pictures you've uploaded aren't that sharp which makes it a little tricky to be specific. There is sign on all of the parts of dirt/debris that has been present which could be due to a lack of cleanliness during assembly. The main bearings actually don't look too bad, although that analysis does depend on exactly what sort of mileage the engine has seen and how much power it was making. There is some light debris damage obvious as noted, however you'll often see a slight polished appearance on the bearings that are visible in the pics you've attached in engines that are making high power levels. This could be reduced by a superior oil or possibly a different grade as it indicates that the oil film strength is marginal.
The engine has obviously been detonating severely and this in turn will beat up on other engine parts and in particular the big end bearings tend to get hammered due to the shock loading. This is normally more apparent on the upper bearing shell than the lower shell. From the pics I wouldn't mind betting that the bearing condition may be related to partial oil starvation or marginal oil film strength. I also wouldn't necessarily take much notice of the bore clearance on a piston that is that badly damaged as it's probable the piston skirt may have been affected. You can however get some idea by checking the bore diameter on #3 and comparing this to the piston manufacturers recommendation.
From my own experience with the FA20 there are a couple of problems that are easy to overlook if you're not aware of them and they can easily lead to damage. The first is that the recommended oil grade is 0W20 which I personally believe is marginal for even a stock engine if it's being driven hard. You'll see oil pressure reach only 40-50 psi at high rpm if you're tracking the car and the oil imho is too thin to support the higher loads of a turbo application. In addition the oil temperature gets very hot without an adequate oil cooler. In stock form we were seeing 140 deg C on the track before adding an oil cooler. Our initial oil cooler was fine for N/A use but we needed to increase the size dramatically when we added a turbo. I'm also running a high quality full synthetic Motul 5W40 oil now.
Hi thanks for the reply.
The engine shown ran around 15hrs race conditions at high power levels. There were some oil pressure drops due to a sticky PRV in the dry sump oil pump. The oil used is 15w-50 with an oil cooler. The temperature of the oil entering the filter housing is 80'c.
The map is currently being looked at to pursue the detonation. So i am starting the rebuild of this engine now. The block is being replaced with a brand new item.
I am getting piston to bore clearances of :
Cyl 1 - 0.675
Cyl 2 - 0.675
Cyl 3 - 0.07
Cyl 4 -0.07
Choosing the minimum bore diameters from my mesurements
The specified clearance by the piston manufacturer is 0.762.
Do you think these clearances are acceptable or does it need a bore?
Thanks in advance.
Oil surge will very quickly result in damage in a high power engine so that certainly needs to be addressed.
I'm going to assume that you mean 0.0675 and 0.0762 as your specified clearance? It's hard to add much to this without knowing the piston manufacturer, however I'd certainly not recommend going tighter than their spec. 0.0762. This is already quite a tight piston to bore clearance for a 2618 forged piston. Particularly if you're seeing signs of wear on the piston skirts I'd be inclined to increase the clearance very slightly.
Hi. Yes a new oil pump is going on.
Piston manufacturer is carillo. Yes sorry they specify 0.0762.They block is going off for honing.