Guest Paul Felker Posted August 27, 2002 Share Posted August 27, 2002 Hello everyone, in my earlier post i wanted to put a n42 head on a 260 short block. but im going to run into problems, the motor that is in my 78 280z is a f-54 block with a p79 head on top. well the motor turs out to have a rod knock !!! well any ways i got over that, now can i put my 260 short block in and use the p79 head and use the 260 head gasket? or is that too much trouble the reason for all the questions is im just trying to patch a motor together untill my turbo motor is complete.. so can this be done or what??thankyou for your patience Quote Link to comment Share on other sites More sharing options...
Mike C Posted August 27, 2002 Share Posted August 27, 2002 From my limited knowledge, I believe the 260 and 280 have the same bore (while the 240 and 260 share the same stroke?) and the N42 has same size chambers as the late E88 so valve clearance should be fine on the bore and compression should be stock. Please get confirmation from somebody else! Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 27, 2002 Share Posted August 27, 2002 Actually, Mike you have that backwards. The 240 and 260 share the same bore, the 260 and 280 share the same stroke. I bet you will find that the P79 head will not give you much in the way of compression on the 260 engine. You would be better off in this case to run the N42 (yeah I know I am going to get some static for this advice). That said, if you milled the P79 and shimmed the cam towers to comprensate and adjusted the lash pad thinkness, the P79 would be a better choice, but for simplicity's sake, the N42 makes more sense for you. You are losing 3mm worth of bore diameter between the 260 and 280, and a P79 gave mid 8's to one compression on a flat top 280 engine which is why I think you should leave the P79 off. I am going to be putting a milled P79 with a large cam on a 260 bottom end this weekend, and can let you know what I end up with. Quote Link to comment Share on other sites More sharing options...
DAW Posted August 27, 2002 Share Posted August 27, 2002 Step back and think about what you need and what you don't, in order to achieve your goal. "More" can be less...a P79 head on a L26 is good only if you're turbocharging it as the compression will be abysmally low. If you've got the P79, can we assume your car is f.i.? I'll cut to the chase, the best performing head for your application (and already set up for unleaded gas and f.i.) is the Maxima L24, N47 head (NOT the 280Z, N47 as it is totally different). Use it as-is or swap in the cam from your P79 (and matching rockers/lash pads) and swap the intake valve springs from your P79. If you do this you will have the strongest, otherwise stock, L26 you can put together for very little money (Maxima heads are cheap and abundant in JYs). An N42/N47 (L28) head will yield a stock L26 c.r. P79 is way too low a c.r. Maxima N47 (L24) head will put you at about 10.2:1 with less tendency to ping than an E88, E31,or N42 would at the same c.r. If you want to drop the c.r. by .5 or so, you could run 2 head gaskets (I've never done this but 12 sec SU Norm says he often does this). DAW Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 28, 2002 Share Posted August 28, 2002 Don't tell me Norm runs 2 head gaskets. I have got to say, I think that is really a bad idea. Does he advocate doing that? Buy the headgasket from HKS or NISMO and be done with it. It comes in less than 1mm thickness, 1mm and 2 mm thickness. If you blow out two head gaskets, by the time you replace the head gasket(s) and put it all back together, you will be way ahead with the Nismo or HKS gasket. I think they are reusable too. I need to scope out this Maxima head deal, although since I have gone thru the trouble to mill and set-up my p79, I am going to run it just the same. Sounds like setting up the Maxima head would be alot simplier, and I could just have the valves replaced with the one's in my P79 and go to town. Might need seats though. Quote Link to comment Share on other sites More sharing options...
Guest Paul Felker Posted August 29, 2002 Share Posted August 29, 2002 thanks for the replys guys, ive been thinking, the motor in my 78 is a f54 block and i have a p79 head on top it has a rod knock, turns out that i have another f54 block in the garage, how bout if i used the crank rods and pistons out of that block and used them in the motor thats in my car?? the motor in my garage dosn't have a head on it and it got some light rust in a couple of the cylinders, but you can still see the cross hatch marks in the cylinders so i don't think it had all that many miles on it. so are all f54 guts the same, like the cranks rods and pistons? and can i use the piston rings off of the pistons that are in my motor and put them on the pistons that i plan to put in? reason im asking this is maybe there is something wrong with one of the rods, like bent or twisted, hence the rod knock!! so i put my other crank in with all new bearings and new gaskets and i should be in business right? last could a rod knock make a motor skake? my motor shakes a reasonable amount and you can hear the knock getting a little louder(this motor is supposed to only hve about 6k on a rebuild) this all started when i first gotthe car and the auto tranny input shaft was broken off and the car wouldnt go at all(DUH), so i converted to a t-5 got all that finished finally and it still shook like crazy, did a complete tune-up and still ran the same, then we started to putz with the timing and like magic it almost cleared up, but the you could hear the rod knock a tiny bit, ran it longer and you could here it more. so that it where i stand at this moment, sorry for the rambling, ill go away now, thanks again for the posts guys. Quote Link to comment Share on other sites More sharing options...
DAW Posted August 29, 2002 Share Posted August 29, 2002 You're making my head spin! What the **** are you trying to accomplish? Why not use the F54 short block you have in the garage? Don't sweat a little surface rust on cyl walls from sitting...take some Kroil penetrating oil, a super fine drywall sanding screen, and freshen up the walls using a horizontally circular motion, followed by wiping with a clean cotton towel. "Rebuilt" is not a good thing; run away! If you do use the F54 shortblock then forget about the Maxima N47 and use the P79 (or an N42/47 from an L28). DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted August 29, 2002 Share Posted August 29, 2002 You're making my head spin! What the **** are you trying to accomplish? Why not use the F54 short block you have in the garage? Don't sweat a little surface rust on cyl walls from sitting...take some Kroil penetrating oil, a super fine drywall sanding screen, and freshen up the walls using a horizontally circular motion, followed by wiping with a clean cotton towel. "Rebuilt" is not a good thing; run away! If you do use the F54 shortblock then forget about the Maxima N47 and use the P79 (or an N42/47 from an L28). DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted August 29, 2002 Share Posted August 29, 2002 Lockjaw, I think you should check out the Maxima N47, but maybe for a future project, I wouldn't abandon a P79 you've already milled. BTW you can't swap P79 valves into the N47 Maxima head because they're too short. That is basically the crux of it though, the P79 valves are shorter because the chamber roof has been raised by that amount, decreasing c.r. The Maxima N47 is basically a P79 with the roof dropped down, something that big milling of a P79 duplicates but from the other direction. DAW Quote Link to comment Share on other sites More sharing options...
Guest Paul Felker Posted August 30, 2002 Share Posted August 30, 2002 Daw don't blow a gasket ok? i just noticed that i had a f54 block in my car 2 days ago, when i took the fuel injection off thats when i saw the f54. Im going to have a kid in a few days and i want to get this stupid car on the road before that happens cause i know ill have NO time to work on it. the reason i want to put the spare crank and rods in is that i already took them out of the block in my garage. Im trying to save as much money as possible as ive already spent almost $800.00 in just putting the t-5 in my car and i still cant drive it!! plus i don't want my wife to have a **** hemorage if i keep throwing heeps and gobs of money at this thing with a new born knocking at the door! anyways sorry to piss you off Daw thanks as always for you guys' time Quote Link to comment Share on other sites More sharing options...
DAW Posted August 30, 2002 Share Posted August 30, 2002 Hotshift 13, I'm not pissed off I'm just trying to help but I don't want to misguide you. There's enough displacement difference between the cylinders of the L26 and L28 that the cyl head recommendations would not be the same for both blocks. I didn't know that the engine in the garage was diassembled rather than an intact shortblock. Why is the shortblock with the rodknock better than the garage one? I'd be apprehensive that if a rebuilt engine has a rod knock that it wasn't done properly and there may be other problems (like, do the pistons match the bore? do the rings match the piston dia., etc). Do you want to use the bareblock F54 from the car because it was freshly honed? The Nissan engine factory puts these together with finely matched individual piston to bore clearances and the cyl walls are very durable. You might consider putting the garage engine back together, using the new rings and bearings from the car engine (make sure they are std. size) and put the pistons back into the cyls they came out of. Congratulations in advance for your baby! In the interest of expediting the car repair, just focus on getting an F54 in there and use the P79 head. Good luck and let us know if you run into a problem. DAW Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 30, 2002 Share Posted August 30, 2002 Man I would be getting excited too. First of all, your rod knock is likely due to the rod's big end being out of round, and it may or may not have spun a rod bearing. You would have had to have something major happen to bend a nissan rod. You should never re-use rings, new one's are less than 100 bucks, and trying to remove rings from one piston and moving to another is a bad idea. If you are worried about the cylinders, run down to a parts store and buy a hone (30 bucks), hone the thing out and put new rings and bearings in it and go. You should also use the P79 head on the 280 engine, but on the 260, you should use the N42 as previously stated. A properly tuned and mechanically sound inline six should not shake at all. If it has a larger camshaft in it, that will make it shake, but in your case, the shake is likely due to the rod knocking issue. Daw, so if the maxima head uses longer valves, seems to me I could take valves out of a Z n42 head and get larger seats installed in the maxima head. I am going to have to look into this because it would be a way to skip the huge amount of milling we are doing, and it gets rid of those cam tower shims. Plus, i could actually mill the maxima head and make some maor compression. Quote Link to comment Share on other sites More sharing options...
Guest Paul Felker Posted August 30, 2002 Share Posted August 30, 2002 hey guys thanks, i think will put the short block in my garage back together again(i knew it would be a bad idea to take that one apart !!!!!)SO i figure ill go to the parts store and get a honing tool and clean up the clyinder walls real lightly, and put the pistons back in with the old rings bearings a new gasket set with the p79 head. the old rings should be alright right, cause you can still see the cross hatch marks in this block(and a little bit of rust), and cleaning them up should be just fine right? oh DAW im glan i didnt upset you i should type my questions a little bit more clearly(I hate to type ) thanks guys Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 30, 2002 Share Posted August 30, 2002 I don't like the idea of reusing rings, but it is your engine. It is not uncommon to see crosshatch on datsun cylinders after a lot of miles. Why not just get a set of sealed power economy rings for about 55 bucks, ( part number E-488k) and make sure the thing is sealed up right? Seems to me it is cheap insurance, and a lot less hassle then taking the engine back out for oil consumption problems. I would not hone it if you are reusing the rings, just put them back in CAREFULLY if that is the route you choose. I don't think scuffing the cylinder wall is a good idea if the rings have already seated, but that is me. I would get some new rings and hone it. Thats my 02. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 30, 2002 Share Posted August 30, 2002 I would not use the old rings even if you can see cross hatch on the cylinder walls. I rebuilt my L20B and allowed my brother to abuse a fresh engine. After about 2 months ,He sneaked it back with a blown head gasket. When I changed the head gasket, I could see the cross hatchs in the cylinders that I had earlier done...... And the engine learned how to begin burnning oil after the head gasket replacement. Quote Link to comment Share on other sites More sharing options...
Guest Paul Felker Posted August 31, 2002 Share Posted August 31, 2002 so ill still use the old crank and rod bearings get a set of the sealed power rings, hone out the cylinders with one of thoes things that put the cross hatch marks in, with a new gasket set and put it all back together. now remember this motor dosn't have to last forever, just untill i finish putting my turbo motor together. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 31, 2002 Share Posted August 31, 2002 No sense playing around with an oil burning pig. You can reuse the bearings as long as there is no copper showing, if there is copper showing, they have to be replaced as well. Good luck with it. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 31, 2002 Share Posted August 31, 2002 There is this plastic thread called plasti-gauge that you place across a bearing half ..then re-torque...unbolt and measure the crshed plastic thread with the plasti-gauge scale on the paper wrapping to determine bearing tolerances or in other words if the plastic thread is really crushed and spread out the bearings are good.. easy to use //simple to read Quote Link to comment Share on other sites More sharing options...
Guest Paul Felker Posted September 1, 2002 Share Posted September 1, 2002 Well i finally got around to pulling the motor out and got it on a stand, and what do i find? every one of the main bearings were spun or squished or just plain screwed. the rear bearing was so bad that they actually spun together to make 1 half bearing. the rear one was the worst and they got less worse as i worked my way to the front of the motor and even the front one was in bad shape. the rod bearings were in like new condition except for #5 that one was spun too. oh well back to the drawing board. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 1, 2002 Share Posted September 1, 2002 (from the condition of the engine)You must have loaned that car to my brother. Quote Link to comment Share on other sites More sharing options...
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