2013 1.8l Prius cylinder head gasket replacement

Can someone tell me what the average roughness Ra of the cylinder head deck should be in order to seal properly with the 3 layer metal head gasket? This cylinder head is just about perfectly flat but has a small scratch touching the number 1 cylinder opening. I can't catch my finger nail on it but I'm worried that touching the cylinder opening, it could allow hot gasses to penetrate. Gasket I am planning to use in from Felpro and I'll probably run this by them as well.

On a related subject, is it likely that an auto machine shop will produce the correct surface finish? I was thinking I could do that myself with sandpaper glued to a hard flat surface, maybe twice the surface area as the head.

 

I've looked a bit more carefully at cylinder number 1. This was coincidentally the cleanest piston but I was thinking this was caused by a head gasket defect. The car has 127K on the original motor so I figured a head gasket problem might account for all the coolant that was getting lost. Anyway, the number 1 cylinder has two polished/scored vertical stripes on opposite side of the cylinder, about an inch wide. It can't be detected by touch but it's clearly visible. Other parts of the cylinder and all of the other cylinders have the cross hatching expected on a motor in good condition. I put a couple ounces of rubbing alcohol in each cylinder and they all seem to hold it well...no leaking. No oil burning was seen before the head was removed. But, I'm worried this wear pattern will continue and eventually cause a problem. I've read that there are counterweights on or near the piston rod to prevent cylinder wall wear but don't know whether these could have fallen into the oil pan. The motor is factory original.

 

Talked with felpro technical about average roughness on the head and they said their gasket will work well with anything below 60, if I recall correctly. The shop I used typically does 14, although they can dial in other numbers.

 

Could be. I'm really not an expert on this. My understanding is that the Toyota spec is 30 to 60 ra which means average roughness and has to do with surface variations over specific distances. Felpro told me today their triple layer metal gaskets for the Prius work with anything below 50. Any roughness from that number down to a mirror finish will work. There is a special tool to measure surface roughness

 

Felpro told me today that any average roughness 50 or less will work with their Prius gasket. Most machine shops have a tool that will measure average roughness and apparently they aren't cheap tools.

Sorry, I duplicated a post or two here but can't figure out how to delete these last two.

 

I have taken the Prius on a long drive...maybe 30 miles, city and freeway. It runs great with no trouble codes, although it does say "maintenance required" along with odometer mileage in the box. I need to reset this but haven't found good Gen 3 instructions.

Now the possible trouble. I think there might be a little oil/coolant mixing going on but I'm going to drive it a bit more to be sure. I'm hoping this was just some old stuff left in the block? Is there anyplace other than the head gasket where this can happen? I do recall that when I took things apart, the intake manifold was completely coated inside with the chocolate milkshake situation. I think I got most of this cleaned out but maybe it will just be sent out the tailpipe. There was also a fair amount od white smoke on startup, both under the hood and through the tailpipe but that seems to be gone now.

 

while the Prius seems to run well and does not smoke, it does have the dreaded white foam under the oil cap and I think it is losing coolant. One thing I am concerned about is the head gasket. When I had incorrectly torqued the head bolts, the Felpro tech advisor to me to remove them, check their length, and then install them again. He said the triple layer metal gasket would be fine and all the bolts measured within spec for new ones. ImI thinking this is the neighborhood of the problem but wondering whether it could be something else and whether there's a way to tell for sure without taking it apart again. I could do a compression test.

 

I also thought of pressure testing the cooling system on the theory that this might inject coolant into the problem area or areas, although this would be far lower pressure than combustion pressure.

 

I called Felpro which made the head gasket kit and the bolts. They had a spec for bolt length min and max for new bolts and max length for stretched bolts. The guy I talked with was somewhat cagey about my question and required me to read a number off of the box before he would answer. Unfortunately, I did not write down the number so if I call them back again, I will get that. I will say they are quite helpful and I think they are all ASE mechanics.

 

The other thing nagging at me is a spec of 30 to 60 rA for average roughness of the cylinder head deck. Felpro also to me smoother is better for average rouhgness. The machine shop routinely uses 14 rA which is pretty much a mirror finish and below the minimum specification. Obviously, going over a max roughness spec could cause head gasket seal problems but what about too smooth?