J13 rebuild options.

[R4wb33]

Got my head pulled off my j13. I had compression tested it and had between 140-150 on cylinders 1,2,3 and 45 on the 4th. The cylinder with bad compression has the cylinder scored where I guess the ring gouged it. What’s the easiest repair at this point? Bore cylinder with oversized pistons? 

 

[wayno]

Can you feel them scratches with your finger nail?

[R4wb33]

Yes I can feel them. 

[zed1]

Do you have a machine shop nearby that could give you some recommendations?

Keith

[difrangia]

Where are you in Oklahoma ?

 

[R4wb33]

Ardmore Oklahoma. I do have a couple of machine shops nearby my concern is finding the oversized pistons and rings. Havnt seen much. 

[datsunrides]

It looks like there may be stampings on top of the piston that indicate it’s been bored out already. It would usually have something like .030 (inches) or maybe 1.0 (mm). Couple points I can make are if it’s already been bored out, check your head gasket to see how much larger you can bore it before the head gasket won’t seal. Most motors can go .060 over before a sonic check is in order to make sure the cylinder walls are not getting too thin. If the damage to that cylinder is too much to fix with a bore job, you can always consider a liner. Finding off the shelf oversized pistons will probably take a bit of hunting, most likely via forklift part suppliers but you can always get custom pistons made, but at a cost you may find unacceptable.

[datzenmike]

 

 

Not a ring or it would scratch up higher. Looks like the piston pin came out the side. That's DEEP.

[difrangia]

I believe datzenmike is right; looks like wrist pin score going by size and radial location. Keep in mind that E1 (1200cc) engine uses same piston as the J13 (1300cc) engine. A12 engine uses same piston dimensionally but has a dish in the top that will lower compression just a little. I scrounged 2 1/2 sets of oversize pistons about five years ago from Ebay when gathering stuff to rebuild my E1 engine. Used a set of 1.5mm oversize pistons. Sold the set of 1mm over A-Series pistons. Still have two new oversize Australian pistons with rings & pins. I'd have to take a look to see what oversize they are. Keep em in mind. 

 

Some British pistons might work. That J-Series engine is close kin to Austin-Morris engines of the period. Take a look at the page link that I'm attaching. It may have some interchange possibilities. BTW I'm in the McAlester area.

 

http://www.farm.net/~mason/datsun/datsun-parts.html

 

[difrangia]

Did a quick look on Ebay and here's a couple listings you might take a look at. 

 

https://tinyurl.com/qlk8scr

 

https://tinyurl.com/t7e5c38

 

https://tinyurl.com/qw3afea

 

Edited February 9, 2020 by difrangia

[R4wb33]

I had seen the first link. I assume the plus 1.0 is mm? That’s about .039” I hadn’t seen the 1.5mm that’s .059”. 

[difrangia]

Correct, R4wb33, although most everything on the old E & J engines are SAE inch measure, the pistons are usually marked in mm, I think. 

 

I use .03947 for converting mm to inch. A 1mm oversize might clean up your cylinder gouge. That would be .020 material removed. Thats a fairly 'Nasty Gash'; might take the 1.5mm to clean it up.

[R4wb33]

Just looked at the piston tops again and they all say “ra2561 std top 0.03 rh” does this mean it has already been bored .03”? How much further could I go safely or is a different block better at this point?

 

[wayno]

That STD makes me think they are not over bored.

[R4wb33]

I think I’ll try and pull the block then and see how much the machine shop needs to clean it up. Buy the pistons after they tell me how much to bore. 

[Rushnracin]

Arias pistons has the ability. They already have cad models for a set of 060 overs that i had make just a few years ago. My situation at the time was. Oversize forged pistons verses  the cost of sleeving and new std dia. cast pistons. Sleeves were $100 a hole installed.  I tried for months looking for a set. From what i found forklift pistons  were long skirted 3 compression ringed.   mike has more info than i but just my 2 cents. 

[datsunrides]

I would say the pistons are standard. Not sure what the other stamping means. If it was .003 then I would say its an oversize piston for std bore as they make slightly oversize rings for when the bores need to be cleaned up with an aggressive hone (like for a small taper), but not bored. Rushn is right that sometimes it is better to just get the pistons made. It was a while ago but I had some forged JE pistons made for a U20 engine for I think $400/set. Kind of hard to justify spending that coin on a J13. When I had my 520 and needed to re-ring it, I strongly considered looking into whether it was a drop in to use a MGB 1800.

[datzenmike]

It's almost impossible to mill a perfect size piston diameter or a block bore. What they do is measure both an assign a grade number. A piston that is 0.03mm over size is matched to a bore that is 0.03mm too large. It speeds up the assembly and cuts down on rejects.