Any engine builders out there? I finally got my engine block back from the machine shop. Reassembly is underway. Up to this point, everything has been perfectly in spec.
The block was bored 0.020 over and I bought new 0.020 over Hepolite pistons (9:1 compression). I pushed a few of the rings into several of the bores to see if the ring gaps are in spec. The Jaguar service manual says that the gap in the compression ring should be 15 to 20 thou and the oil control ring should be 11 to 16 thou. All of my compression rings are measuring 25 to 28 thou. Ugh.....
I did a lot of research on the piston to wall clearance as I saw in several place on this forum and elsewhere that the service manual numbers are too tight for the Hepolite pistons. After much discussion and reading, the machinist and I decided that 2.5 thou would be a good choice. Is it possible that the ring gap on the Hepolite supplied rings would also differ from the service manual? Does a max of 28 thou seem reasonable? I don't see any technical help lines for Hepolite so I'm not sure that I will get an answer from them.
Any input is appreciated!!

 

My machine shop reccomeded using a set of Hastings rings, with the Jaguar specified end gaps.

Hastings specifies for 75-90 mm bores (the 3.8 is 87mm) the end gaps should be 0.010-0.020", so .028" seems big.
Their base part number for a 3.8 ring set is 5957, for 20 over it would be 5957020

 

Thanks, Jagboi. I did find a customer service email for Hepolite. Hopefully they will get back to me first thing on Monday, say "sorry about that" and get a correct set of rings in the mail right away. I think I will start to look for the Hastings rings in the meantime.

 

Have you measured your bores for size, taper & ovality? Machine shops are usually pretty good but it's worth checking. You imply it's right in your first post.

 

Hi Glynl. Thanks for the input! I don't have the proper calipers to measure the bores any deeper than an inch or so. My measurements may not be completely valid but I got 3.443 near the top. The spec is 3.425 so I am in the neighborhood of a 0.020 overbore with my limited measuring abilities. I measured the piston at the bottom, 90 degrees from the wrist pin and got 3.445 which fits with the 0.0025" piston clearance we were shooting for. Even without the extra 0.0015 bore to accommodate the Hepolite pistons, the ring gap would still exceed the upper spec of 0.020" by a few thou. An extra 0.0015 of bore would lead to an increased circumference of 0.0045". My gaps are consistently 0.028" and subtracting the 0.0045" would still be 0.0235 or 0.0035 over the spec.
The machine shop came highly recommended from a fellow Jaguar club member and based on the number of questions and the amount of time he put into the piston clearance question, he did not rush this job.
The specs I mentioned in the first post were for the crank end thrust and the main bearing clearances. Both were right in the middle of the specs.

 

Understood. Seems fine.

 

https://www.practicalmachinist.com/i...ht-bore-gauge/

 

That takes me back to when I was an apprentice with the British Steel Corporation. The old chap who ran the apprentice machine shop made us do lathe work down to a few thou using calipers and a steel ruler. With practice, it's possible; it's very much a matter of calibrating your eye.

 

I love it when I have an excuse to buy a new tool! Thanks for the article!

 

Do all of the three ring type pistons (OE Bricco, OE AE, Hepolite, Mahle, etc) use the same rings, aside from some of the very early 4 ring pistons? SNG has a set of 0.020 rings IN STOCK (wow!!) and I'm thinking of picking them up in the hopes that I will have usable rings by the weekend. No mention of the brand. I will call them in the morning. I'm worried that if they are Hepolite rings I will have the same issue with an over spec gap. I can't find the Hastings rings in stock but it looks like 3 weeks or so to have them drop shipped.
Any thoughts on buying +30 rings knowing that they will be too long and filing them down? That would pretty much guarantee that they are not too short. I can't imaging that they are any different than the +20 rings aside from the length. I'm rambling......

 

I wouldn't. The rings are circular and when compressed exert a spring force on the cylinder wall. If it's oversized then it won't exert an even force through the spring, and is more likely to break prematurely. That's a real pain to fix. If you can get the right parts from SNG reasonably soon, I'd go with that.

I believe that each of the piston makers make their own rings, but I could be wrong on that.

 

They certainly make or have made for them rings to fit their piston design. All are not all equal in that regard.

 

The new 0.020" over rings arrived from SNG Barratt. They are US made Grant brand and fit perfectly in the bore. Did a quick check on a few compression rings in a few bores and all had a ring gap of 0.012" to 0.013". Interestingly, the oil control rings are all near the top of the factory spec. The Grant rings are identical to the rings supplied with the Hepolite pistons in every measurement (except the obvious "length") and they even come with the "top" marking where it matters and very detailed instructions.
Looks like piston installation weekend!! Thanks again to everyone for their input.

 

Good news!