Too oval bores?

[cygnusx1]

So I measured the bores carefully today and found that they are oval on average by about 0.0012" and the max allowable spec in the FSM is 0.0008". The bores are extremely clean with zero scoring. The taper and maximum bore is within spec. I am on a very tight budget so I plan on doing a re-ring, bearing shells, and a timing kit. I had planned on flex honing and calling it a day. Should I fret over the oval spec? I know leaving it oval is not the "right" thing to do...but what are your opinions. What am I losing with slight oval? Ring sealing compromise? Piston slap? I am going for an OEM L28ET rebuild on my current setup, which is in the 320-350rwhp range at 16psi boost. I am not too concerned if the side effects are minimal. It was running great, albeit, a bit oil consuming (1qt every 1500 miles or so), but that could be due to the 160k mile rings that were in there, no? I didn't do a leakdown or compression test before the motor blew the head gasket. The plugs showed signs of oil too. The downside to boring it is that it will add machining costs and piston costs to the budget, which is a significant cost increase for this particular project.

Edited April 14, 2011 by cygnusx1

[inline6]

I'm no engine builder, but I think it is somewhat common that bores are out of round by .001" even when freshly machined. At least, that is what I recall a performance L series engine builder telling me once. I recall him saying something about his cylinders being rounder than many because of his equipment (and something about honing technique) and that because they were rounder, engines he bored would break in quicker than some. So, I'm sure one of the more qualified will weigh in (and their comments should be worth more than mine), but I'm thinking all you may have to deal with a slightly longer break in period. Other than that, with fresh hone and new rings, I think you will be fine.

[cygnusx1]

Found an informative article discussing cylinder dimensions and wear.

 

http://www.realclass...ch05031600.html

He says that in his experience cylindricity up to 0.005" is workable (on a morotcycle bore), so I should be fine at 0.0012 and just expect slight oil consumption..which will undoubtedly be better than it was with the old rings anyhow.

Edited April 14, 2011 by cygnusx1

[rayaapp2]

So I measured the bores carefully today and found that they are oval on average by about 0.0012" and the max allowable spec in the FSM is 0.0008". .... I am going for an OEM L28ET rebuild on my current setup, which is in the 320-350rwhp range at 16psi boost. I am not too concerned if the side effects are minimal. It was running great, albeit, a bit oil consuming (1qt every 1500 miles or so), but that could be due to the 160k mile rings that were in there, no? I didn't do a leakdown or compression test before the motor blew the head gasket. The plugs showed signs of oil too.

 

Oil consumption can be very bad for your tune esp at high load and cruise. Besides why would you build a "320-350rwhp range at 16psi boost" L series and not make sure it was perfect to ensure longevity of your build? I actually built an L28et with around 320rwhp @ 18psi boost on a modified T3 turbo so I can attest to how critical everything must be for longevity. Slapping stuff back together without taking the time to ensure every little thing is right can and will be the failing point in any build. Now if you were a stocker and could deal with the oil consumption you'd still run into the same issue, but it wouldn't be as critical for longevity.

[rossman]

As you already know, engine specs are not arbitrary. If it were my engine, I'd save up the money and fix it right.

[DRIVEN]

I think you'll be just fine. Remember, we're only talking about around 1/1000th of an inch out-of-round on a component that is almost 3.4 inches. What's that, equivalent to about an inch on a 30 story skyscraper? Another thing to consider is that the bores and the deck surface will change shape slightly once the head is torqued down anyway anyway. The only way to get a truly accurate bore measurement is by using a torque plate. As for the oil consumption, as long as your valve guides/seals are dealt with and your piston's ring groves are clean and within spec you should okay. If money was no issue I would definitely say bore it and use new pistons. You said it's a budget build so obviously you have to make some compromises. Good luck.

[z-ya]

What will the minimum piston to bore clearance be using the worst out of round measurement, not the average? After the rings seat?

[cygnusx1]

I got the block out today and will go over all the measurements again. I'll look for the worst out of round, and measure piston clearances all around. I certainly understand the benefits of pouring money into every detail but I want this thing back together as soon as I can, with as little dough that I can put into it. It survived 6 years as it was, running 14-18 psi, so I think with new wear parts, I can get a few more years+ out of it at 16psi with a real dyno tune and maybe a knock sensor loop. The head is almost brand new, and my hunch is that a fresh lower end, even stock with that little ovality, is very strong.

 

My gray area is the initial question, of how much am I REALLY giving up with the bores ever slightly over-oval spec.

 

I'll spec the pistons and bores out again carefully to make a final decision. Thanks for the thoughts and suggestions!

Edited April 14, 2011 by cygnusx1

[z-ya]

I got the block out today and will go over all the measurements again. I'll look for the worst out of round, and measure piston clearances all around. I certainly understand the benefits of pouring money into every detail but I want this thing back together as soon as I can, with as little dough that I can put into it. It survived 6 years as it was, running 14-18 psi, so I think with new wear parts, I can get a few more years+ out of it at 16psi with a real dyno tune and maybe a knock sensor loop. The head is almost brand new, and my hunch is that a fresh lower end, even stock with that little ovality, is very strong.

 

My gray area is the initial question, of how much am I REALLY giving up with the bores ever slightly over-oval spec.

 

I'll spec the pistons and bores out again carefully to make a final decision. Thanks for the thoughts and suggestions!

 

 

When you say giving up, do you mean performance? I would think that the more out of round the bores are, the longer it will take for the rings to seat. And per my previous post, if the cylinder is out of round enough, the piston skirt could contact the bore once the rings fully break in. What do the pistons skirts look like?

[cygnusx1]

When you say giving up, do you mean performance? I would think that the more out of round the bores are, the longer it will take for the rings to seat. And per my previous post, if the cylinder is out of round enough, the piston skirt could contact the bore once the rings fully break in. What do the pistons skirts look like?

Pete, I am waiting on an engine stand and I'll dismantle and inspect all the parts. Right now I have the head off and measured the bores mid stroke, and 1/4" from the top, wide, and long. As expected, they are wider perpendicular to the crank by about 0.00010" and the worse case is #4 at 0.0015" mid bore. I am confident in these numbers as I double and triple measured. The motor ran great before, other than some oil consumption, some from the turbo, and some from the rings for a total consumption of about 1qt for 1500 miles or so. The head is new for all practical purposes.

 

Here is a photo to show how clean the bores appear.

 

 

 

[jt1]

It will be fine. Bolt the head back on it and check it from the bottom and see what it looks like.

 

jt

[cygnusx1]

Really thinking that Nissan probably didn't even have it much closer than what I am finding. I quickly measured above the swept area tonight, and it was out by just about the same amount. I am thinking that I am well within the "functional zone" for an engine that will never see competition. Or, I am seeing block distortion from not having the head on it.

[z-ya]

Or, I am seeing block distortion from not having the head on it.

 

Could be.

[cygnusx1]

I had a friend of mine stop buy to look at it today, he is a fairly experienced engine builder who taught the subject at a local tech school. He feels the same as I do about it, but stressed that it's imperative that the block and head are also checked for flatness, which I already plan to do anyhow. His thought was that if the block is flat, then leave it alone. If not, then it needs to go to the shop anyhow.

Edited April 16, 2011 by cygnusx1

[z-ya]

I had a friend of mine stop buy to look at it today, he is a fairly experienced engine builder who taught the subject at a local tech school. He feels the same as I do about it, but stressed that it's imperative that the block and head are also checked for flatness, which I already plan to do anyhow. His thought was that if the block is flat, then leave it alone. If not, then it needs to go to the shop anyhow.

 

I think you need to check it with a head or torque plate installed and torqued to spec. It doesn't really matter how round the cylinders are without the head torqued in place. It really only matters when it is all put together.

[Oddmanout84]

Wish I had a torque plate... My block was rebored without one...

[cygnusx1]

OK I discovered that two of my pistons lost their skirts. So I will definitely need pistons. So much for the budget...I called a local machine shop and they will prep the block, boil, bore, hone, deck if needed, for $400. I suppose that really is wise money spent.

[z-ya]

OK I discovered that two of my pistons lost their skirts. So I will definitely need pistons. So much for the budget...I called a local machine shop and they will prep the block, boil, bore, hone, deck if needed, for $400. I suppose that really is wise money spent.

 

 

Sorry to hear that you have to open up that can of worms. At least you now know what was causing the oil consumption. Not sure what your schedule is, but my torque plate is going to Ron St. Croix in Newfoundland first, then it is available if you need it.

 

Now comes the "while I'm at it" costs...

[cygnusx1]

While I'm at it...lol. There is nothing else so true. Not even a torque-plate milled L block. I will ask the machine shop if they have a torque plate for the L if not, I'll keep you in the loop. Thanks for the generous offer!!

 

I ordered the whole engine kit today from RPM Rons. I thought it was a good deal.

 

http://www.rpmrons.com/Nissankits.html

 

$535 for +0.020 ITM Pistons, wrist pins, all clevite bearings, chrome rings, full gasket set, turbo oil pump, and timing kit.

 

I am cleaning up the E31 "A" cam and spray bar, to install in the P90A that was rebuilt last year. Should I bring the E31 rockers over with the E31 "A" cam? Both sets of rockers look good.

 

All I need now is some job interviews to pan out so I can get ahead again.

Edited April 19, 2011 by cygnusx1

[z-ya]

While I'm at it...lol. There is nothing else so true. Not even a torque-plate milled L block. I will ask the machine shop if they have a torque plate for the L if not, I'll keep you in the loop. Thanks for the generous offer!!

 

I ordered the whole engine kit today from RPM Rons. I thought it was a good deal.

 

http://www.rpmrons.com/Nissankits.html

 

$535 for +0.020 ITM Pistons, wrist pins, all clevite bearings, chrome rings, full gasket set, turbo oil pump, and timing kit.

 

I am cleaning up the E31 "A" cam and spray bar, to install in the P90A that was rebuilt last year. Should I bring the E31 rockers over with the E31 "A" cam? Both sets of rockers look good.

 

All I need now is some job interviews to pan out so I can get ahead again.

 

That's not a bad deal. I like the ITM stuff. Their timing set looks like OEM. Depending on the gasket set, you may want to use a different oil pan and valve cover gasket. The cork ones suck. The Felpro oil pan and valve cover gaskets are the best. Clevite bearings are the way to go. Nissan bearings are good too, but the last set I ordered were super expensive (2x Clevite), and I had to return them because they were scratched.

 

I would use the rockers from the E31 cam you want to use. If they are in good shape that is. Same with the lash pads. Keep everything sorted so that it goes back on the same way it came off.