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A15 Rebuild Progress
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Making progress. Crank and cam/lifters are installed. Is it necessary to move the rings around each cylinder before installation to get the best ring gap per specs? If so I do that with all of the rings or just the top 2? Also I noticed a B stamped on the rear main cap. I have another A15 block that has an A stamp. What is the difference if any? One more item, if there is a diagram on how to space out the ring gaps please attach that. Thanks!!

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jpg  block1.jpg (86.39 KB)
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Posted on: 4/11 3:50
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Re: A15 Rebuild Progress
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A and B are casting revisions, dunno what the difference is. They are machined to your block so are not interchangeable without line-boring

Some guys try each ring in every cylinder to find the "best fit", however this is unnecessary. As long as the gaps meets the spec range they don't need to be exact. You could also file the ring gaps to make them all exactly equal

ring gap position is in the instructions. See Piston Rings article

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Posted on: 4/11 5:17
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Re: A15 Rebuild Progress
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So on one of my other threads I mention I am on the top end of tolerances for ring gaps on the top and 2nd ring. Engine was honed out only. I question if honing is the right way to go on a motor that had 150000+ miles. To do this rebuild right should I go for an overbore and get everything within proper tolerance? Found a set of AE pistons .020". Vendor claims they are from Japan. Is this a good brand of pistons?

Posted on: 4/12 4:48
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Re: A15 Rebuild Progress
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did you hone it by hand or did you have a machine shop clean up the bores? I had to find a different A15 block because mine was already bored to .030 over and we couldn't find pistons if I recall....that was like 7 yrs ago

Posted on: 4/16 23:40
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Re: A15 Rebuild Progress
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Had a machine shop hone it for me. DD gave me some info on the gaps that should be checked at the bottom of the stroke and compare it to the top. If it is more than several thousandths difference then it should be bored. Haven't got around to it and plan to do that this week. There is an individual with an MG like mine with the Datsun conversion and just reringed his engine which was slightly out of tolerance. He said after 500 miles one of the rings on #3 cylinder broke. Wasn't sure the cause. If I do bore, replacement pistons do not disclose "dish" cc which concerns me because I want to keep using pump gas. I am using a GX head so compression is going up from the stock H95 head that was on the motor.

Posted on: 4/17 13:53
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Re: A15 Rebuild Progress
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Hi there, are you planning on a long-term build (ie: do it once and use it for high mileage) or is this a race engine (for time attack or short races), because these are either ends of the spectrum.
I've done the quick hone and wash up routine for a race weekend using a moly coated ring and had good short term success but a lot has changed with rings lately.
I would recommend you search the tech areas of several piston & ring makers online. Most are talking about plateau honing and All of them use deck plates for honing and some are even using a deck plate for valve jobs. Also, D-Sport magazine has a recent article series on proper ring gaps, honing and break in procedure.
Bottom line is, IMO, either method will work but the latter method is the one I would use if starting over now. Hope this is helpful.
Quoted from D-Sport article:
Years ago, the common practice was to hone a cylinder with a single grade of abrasive stone based on the type of ring to be used. This left a surface with sharp peaks that provided limited surface contact with the ring creating a challenging “break-in”. Today, high-performance machine shops employ a plateau honing procedure where stages of finer stones or abrasive brush knock down these peaks, establishing a better load-bearing surface during break-in."

http://dsportmag.com/the-tech/educati ... in-the-right-way/#respond

Good luck!

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Posted on: 4/17 18:50

Edited by Lorne on 2018/4/17 19:08:30
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Re: A15 Rebuild Progress
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Honing is the usual treatment for an engine overhaul. Boring is only called for if the cylinders are unusually worn. The machinist should check for excessive out-of-round or excessive taper before he performs the honing. Honing an A15 is good for 125,000 of normal street miles -- even without using a deck plate or plateau boring methods. Using those methods should result in an even longer-lasting engine


Quote:
I am using a GX head so compression is going up from the stock H95 head
H95: 35cc
GX: 29-31cc

Measure your GX head. If it is 31cc, you'll still be able to run on pump gasoline -- up to 11:1 compression. Instead of $2.49/gallon for Regular, pay $2.99 for Premium. The increased fuel economy means the dollar cost will be a wash in the long run. You can run more spark advance with Premium, resulting in more power and more fuel economy

Posted on: 4/18 3:11
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Re: A15 Rebuild Progress
No life (a.k.a. DattoMaster)
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The stock A15 pistons have a 6cc dish and aftermarket 10cc dish. With a 27cc milled GX head and the 6cc dish my next A15 calculates at 10.64 to 1.

OK this is shameless but I have an A15 flywheel lightened to 14lbs I'd let go stupid cheap. It's been in my parts stash for ages. I've used a 14lb flywheel for years in the race coupe and find it works well. A nice mix of tractability and response.

Posted on: 4/18 5:15
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Re: A15 Rebuild Progress
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Lorne-excellent link and understand that at initial startup it is critical to keep the rpms around 2000 until coolant starts flowing for proper seating of rings. I found a set of original cast iron Nissan rings for the A15 from a dealer. My goal for this motor is a long term build. The article touches on ensuring all systems are optimal so that the engine maintains the rpms, especially carburation. That leads me to the dual Hitachi's I have. Not knowing their condition, do I put the original H95 head with stock carb for the breakin period and once that is done, then remove and replace with GX head and dual Hitachi's? Those carbs may take a bit to get fine tuned and it isn't something that I should be tinkering with at startup. Not sure on the specifics of the honing that was done but know that the machinist finished with 45 degree hatch marks which were similar to the original hatch marks.

DD...My GX head has been shaved 20 thousandths over the last 40 years. It is now 28cc. A little under your range. Encouraging to hear that honing should suffice for a long time. I still haven't got around to checking ring gaps at the bottom of the stroke. Should do that in the next couple days and report out.

RT...Thanks for the offer on the flywheel, but had mine shaved down to about 15 lbs. MG weighs about 1,600 lbs which is about 500lbs lighter than the 210?? So taking some weight off was appropriate. Guys that have done these conversions recommended doing this. Not sure how your coming up with 6cc for stock A15 pistons. Mine measured 13cc. I have the offset dish type.

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jpg  flywheel2.jpg (50.00 KB)
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Posted on: 4/19 2:45
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Re: A15 Rebuild Progress
No life (a.k.a. DattoMaster)
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The pistons are factory Nissan with off-set dish and I measured them. Way back when member BigE had said that factory were 6 and aftermarket 10. I do recall measure a set of pistons were around 12cc I think they were deep dish nearly the full diameter of the piston.

Posted on: 4/19 6:18
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