[Slick]

Hey everyone,

I'm rebuilding the bottom section of my G13a engine in my 1986 Samurai. Currently, I've gotten to the stage of installing the new piston rings but I'm at a stand still because I don't know what the correct end gap measurement should be.

I will be grateful for any assistance on the issue. Thanks in advance.

Slick

 

[fordem]

Ring end gap...

Top ring - 0.20~0.30mm
2nd ring - 0.20~0.30mm
Oil ring - 0.20~0.70mm

 

[Slick]

Wow...that's fast...thanks alot fordem.

A few other things:

Honing - is it recommended to hone the cylinders before installing the pistons?? The reason I ask is because there seems to be a lot of mixed feelings about honing cylinders.

Break in procedures - same as honing, there are a lot of different and opposing ideas about properly breaking in an engine with new piston rings.

Regards,

Dill

 

[fordem]

Factory service manuals don't have any recommendations on honing, or break-in, although I believe break-in is covered in the owner's manual (which I don't have) - if you want my personal recommendations, I would bore very slightly undersized and then hone to the required dimensions, honing gives a better surface finish and a cross hatch pattern that supposedly holds oil and improves the break-in.

Manufacturer's break-in is usually nothing more that a warning to limit speeds for the first thousand miles or so, and not to allow the engine to lug, my preference is to limit engine rpm and load for the first few hundred miles, and to raise the rpm limit gradually, brief higher rpm runs are permitted and in fact encouraged, as long as they are not sustained or repeated.

Accelerating briskly through the lower gears allows the combustion pressures to "load" the rings against the wall, helping them to seat.

Don't forget to retorque the head bolts at the first service.

Question for you - is this a re-bore (oversize piston & rings) or a re-ring job - my suggestion on honing does not work for a re-ring job, but, if you're not boring, honing is even more important because it breaks the glaze on the cylinder walls, and so allows the new rings to seat properly - the issue becomes how much can you hone without developing excessive clearance.

 

[Slick]

Thanks for the advice.

I'm only actually doing a re-ring job along with changing my valve seals. I just got the service manual for the jeep so i will search for the break in process. I can't seem to find any mention about honing the cylinders in the section that deals with installing new rings but I will take your advice about deglazing. There seems to be some brown / goldish marks on some of the cylinder walls to. Will try and take some pictures and post them in a few minutes.

A friend of mine reminded me about re-torquing with first servicing a few days ago .

Slick

 

[Slick]

Here are the photos of the cylinders I promised. What do you think?

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[Max]

A "Flex Hone" may better serve your glaze breaking needs.

I can't attest to the fitness of your bore and pistons though with regard to being concentric, having excessive wear (size) nor cylinder taper. :huh: IF that is an issue now, it won't get any better, with new rings.

 

[Slick]

Ok but what are those brown marks from??

 

[Max]

How long has the engine been open to the atmosphere? Looks like just a light surface rusting to me, is all.

 

[fordem]

My suspicion is rust - I would also suspect you have quite a bit of wear on those bores - notice there appears to be a "ring" at the top edge? If you have enough of a ridge to catch your finger nail on, you may need more than just a hone & "re-ring" - have a machinist check those bores for concentricity and piston to wall clearance, anything over 0.004 piston to wall is out of tolerance.

 

[hotrodsami]

Having a shop check you cylinders is a good idea there is just to much that can be missed on a visual inspection alone.

The topic of brake-in procedures can be a hot one, this thread way get busy. The brake-in method I adhere to what some call the hard brake-in method because there is some good science behind it.

Under hard acceleration and engine braking the rings get pushed against the cylinder walls and when you have new rings and freshly honed walls this will ware the rings into the cylinder walls and give you a better seal. After the first hundred miles or so the cross-hatching on the cylinder walls get will loose its sharpness and will no longer ware the rings as effectively so if you don't load the rings up hard enough early you loose the chance to get the best seal.

To brake it in hard when you first get your motor assembled and running let it warm up to normal operating temp. and then find a empty road where you won't disturb the peace (can be done on a dyno) put it in second or third at a low rpm then floor it until it hits the red-line then take your foot off the accelerator and let the engine slow you back down to where you started. Do this two or three times and watch your temp don't let it get to hot (more of a problem when on a dyno) after doing this avoid holding a steady throttle until around 500 miles.

No matter what any one says here it is your rig so brake it in as you see fit.

 

[Slick]

Hey,

The engine has been opened for about 2 days now but i haven't cleaned the cylinder walls yet so there is still oil on the walls. The marks were there when i removed the head and cylinders.

The rings at the top are stain from the carbon that i removed to get the pistons out. There wasn't much carbon though. It would be quite difficult to get the block to a machine shop as it's still in jeep and the nearest shop is about 20 miles away.

Dill

 

[Max]

Lets go back to square one. Why did you originally pull the engine apart? Did it use oil? Did you find any broken rings? Rework the head to include valve stem guide work? Are the cylinder walls scored? You already know how I feel about checking the pistons and bores for wear.

 

[Slick]

Max

I bought the jeep from an OLD guy (I doubt he ever went over 10 miles an hour, lol). When I got it there were no problems other than the distributor was too advanced and the jeep was very low in power; adjusting the distributor took care of the power issue. I then proceeded to install an MSD Ignition Kit with control box and coil; the jeep was running like my AWD 2L Mazda Familia .

About 2 weeks after that i noticed smoke at start up so right away i changed my valve seals and everything was fine. Then I noticed if i use the engine to slow the jeep I get a puff of blue smoke when I reapply gas. A few times the jeep will just drop power out of nowhere; on close inspection, it's always the #3 plug fouled with oil. I did a compression test and everything was level across all cylinders but the technician suggest that the oil ring on #3 might be bad.

I went ahead and disassembly the engine and here i am now...

The cylinder walls arent scored and none of the rings is broken.

Dill

 

[Max]

Understand.

Your oil consumption may still be an issue though, even w/new rings and stem seals. If the valve stem GUIDES are severely worn or the piston and bore specs are beyond allowable limits, then you won't be able to achieve adequate results.

The mechanic assuming a number 3 piston oil ring problem is a wild ass guess, not based on actual inspection and measuring.

 

[Slick]

So you're suggesting replacing the valves to??

 

[Max]

There are two ways to go about this.

1. A full scale inspection and repair.

2. Replace only the parts that you think may be bad without inspecting for wear (seals and rings only) and then cross your fingers.

We also don't know if you are aiming for a long lasting ride, or a quick fix and drive it for a short while and sell it off, so as not to spend a lot of cash on repairs.

 

[Slick]

I would really like to have a full scale inspection but mechanics here like to exploit people when it comes to stuff like that. If changing the rings doesn't fix the issue and the same smoke conditions remain i will just use it as is and try to avoid too much engine braking. If it gets worst, an engine upgrade will be my next step.

Just after my last post a mechanical engineer friend of mine popped up at my house (wanted some music ) so I had him have a go at the cylinders. His verdict is that the rings I took off are good and in fact he would of used them back if I didn't already bought new ones. He also said that the cylinders are glazed and he is suspecting that there is a high chance this is the reason for the smoke to. He went on and explained why but that's wayyyy too much information to retain in such a short time .

Tomorrow, I'm going to hone the cylinders and start re-assembling the engine.

Thanks for all the help everyone. I will keep you posted.

Dill

 

[Azelgin]

#3 cylinder spark plug will show more oil on a worn motor. The intake runner for #3 is where the pcv valve is. Any blow by from the crankcase is pulled in there and oils that cylinder more than the others. Personally, I would have done a simple compression test first, before condemming the whole engine to a re-ring job. Be aware that the chrome rings you are putting in can be tough to seat properly. Hone crosshatch angle can have a lot to do with how easily the new rings seat. Google it to get the information you need, or, you'll end up blowing more smoke than you did. Good luck to you.

 

[Slick]

#3 cylinder spark plug will show more oil on a worn motor. The intake runner for #3 is where the pcv valve is. Any blow by from the crankcase is pulled in there and oils that cylinder more than the others. Personally, I would have done a simple compression test first, before condemming the whole engine to a re-ring job. Be aware that the chrome rings you are putting in can be tough to seat properly. Hone crosshatch angle can have a lot to do with how easily the new rings seat. Google it to get the information you need, or, you'll end up blowing more smoke than you did. Good luck to you.

Azelgin, I did do a compression test and it was level across all 4 cylinders. This was mentioned in this thread to.