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Need specs for l6 rods


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Ok I need to know the big end width of the l6 rods. A couple of other things though does anyone know the stock weight of a 133mm datsun rod with the 9mm bolts. Also curious on rods with advertised weights does that always include the weight of the rod bolts and or bearings? Sorry if these are dumb questions couldn't find the answers in my datsun books.

Thanks

Jared

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I'm surprised someone hasn't popped up with your answer yet. I don't have this written down but I'll supply a crude measurement for you to work with. I suggest you find the true spec though.

 

I just went out to the garage and found a box 'o rods and grabbed an inches-scale dial caliper on the way. I checked an L18/L28 rod and an L24 rod and I got 1.054" for both, or 26.77mm. Most likely that was 27mm when new but I'm guessing. They had some corrosion so maybe it was 26.5mm new, I don't know.

 

Please return the favor and let me know what you turn up for out-sourced rods in a useable big-end dia. that are equivilant or slightly larger than that spec. I remind you again to avoid V6 sources as they will likely be too narrow.

 

Regards,

DAW

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Well I have a set of mr2 3sgte rods in front of me and another set on the way 95 dollars total for both sets. They seem to be pretty thick. I heard they are very strong rods and looking at them I can tell no different. If I could find my stupid micrometer I could measure them. They look big enough by eyeballing but we know how far that will get us. I would like to compare weights one them though. I plan to have them polished and race prepped if they will work for me. They are almost 138mm in length so that should provide a much better r/s with the ld28 stroker combo. They are also bushed for floating pistons stock so these should be good for my ross pistons unless I find out of some stockers that will work. That would be even better.

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hmm according to this link: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7922456956&category=33623

 

The 3sgte big end width is

1.055 or 26.797mm

Meaning they are close so they may not need to be resized at all. Just would like to reiterate what I posted in the stroker thread that the 3sgte have a crank journal size of 1.889 which is also very close to the L series journal only a small amount of crank would have to be removed insuring that the crank retains in structural integrity.

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Excellent work, Jared! (although you may have just doubled the price of used 3sgte rods).

 

0.078" is a lot of grinding on your crank journals so you need to try to minimize that through thinner-walled bearing shells and big-end rod resizing.

 

If you already know, don't be insulted but when a rod bearing is spun and the surface of the big-end is torn up, a machine shop can remove material from the mating surface of rod-to-cap thereby reducing it's diameter. It is then machined to restore the original dia. to match the o.d. of the bearing shell. The center remains the same in location but there is a (minimal) loss of big-end material in the process.

 

So theoretically, you could have the big-ends of the 3sgte rods bored to a size matching the shell o.d. of an alternate choice of rod bearing which has an i.d. of larger than 1.889". I doubt you could bore it so far as to meet the o.d. of the Nissan rod shell without weakenning the Toyota rod, but you might be able to find a bearing closer to 1.967" i.d. with the appropriate shell width, oiling hole location, and tang configuration matching the 3sgte rod's which would fit the rods you have resized and afford less crank journal grinding/weakenning. DAW

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lol a partner in crime. If you have trouble finding another set assuming these work I know where to get a set for 65 shipped. A good machine shop may know of an alternate bearing. I really dont know where to start looking for one though sounds like a big job. Would be nice to not have to cut the crank though.

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Hey Jared,

I received my 3S-GTE rods and they look like they'll fit the niche nicely. I checked on other rod applications which would fall between the stock L6 journal dia. and the Toyota journal dia. and it looks like there were some Volvos (B23?) with around 1.925", which falls between 1.967" and 1.887". I think I stumbled on some 4 cyl Isuzu rods (4Z series) which could also potentially provide bearings for a modest grind of the Nissan crank.

 

However, I was struck by how relatively inexpensive it is to have crankshaft rod journals offset ground. What makes the most sense is to have the L6 (or L4) crank rod journals offset ground in the process of reducing their dia. by 0.080" (2mm) from 1.967" to 1.887" (in order to use the Toyota rods). This increases stroke (and thereby displacement) to the engine. An offset change to rod journal throw center doubles the distance of actual stroke change.

 

So the math...an 0.080" reduction in journal size done eccentrically, towards the outside of the throw, means that the journal centerline has been displaced by 0.040", increasing the stroke by 0.080" total. That means an L28 crank goes from a stroke of 79mm to 81mm, and an L18 crank goes from 78mm to 80mm. The Toyota rod length of 137.4 yields a rod/stroke of about 1.7 on the offset-ground L28 crank.

 

What's left is to find a set of pistons which suits the choice of n/a or turbo application. The 3sgte rods are full-floating 22mm pin. The piston selection is the final variable to nail down and then the block gets overbored (or not) after the piston dia. is selected from available sources. Budget dictates whether an OEM std. dia. piston from a JY core engine, or an aftermarket forged, hypereutectic, or cast OEM-style (but in o.s. dia.) will be the source. Delivered to your door vs rooting around in a JY is not an insignificant accessibility factor either.

 

I think I'll put together an L18 using this approach because I have one sitting around which I'll use in one of my PL510s as I have aluminum flywheels, etc., which won't work on the 6-bolt cranks of the larger L4s and I may want the shorter block to meet some vintage class requirements (vs the taller L20B, LZ20 & LZ22 blocks). This will be essentially equivilant to an L28 crank/block build (except for 78 vs 79mm stroke difference which means piston choice compression ht. for the L6 needs to be 0.5mm less than what I come up with for the L18 if the piston deck hts are to be the same in the calcs.

 

Theoretically, this approach would provide an approach to building an L6 mildly stroked to 81mm (between stock [79mm] and LD28 crank [83mm]), increase the ratio of rod/stroke, and allow a wider selection of piston choices than using L24 or L28 rods which are press-fit 21mm pins. DAW

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Addendum: BTW, using the above approach while using the LD28 block/crank foundation, stroke could be increased from 83 to 85mm using 1.887" big-end rods with the cap width of the 3sgte rods, L4-L6 rods. The rods would be around the 152mm range and the r/s would be relatively high, around 1.8 or so. DAW

 

 

(of course this could be done in an L28 block using L28 rods (130.2mm) and yielding r/s of about 1.5 if you want a r/s in that range). DAW

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Jared, Waterhouse Motors in Tacoma, WA will do the L18 crank for $100 ($25 per journal), so I'd assume an L6 would cost $150. I think that's the going rate because I saw a price listed in a racing engine site that does domestic 8cyl cranks for $200. I'm going to pick up Toyota bearings for the rods, have the crank ground and start searching for pistons. DAW

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Thanks for piping up Dan I was hoping for some concrete numbers in that department. Still weighing in on whether I want to risk that or not. If I can play with bearing sizes as DAW has mentioned Im hoping to maybe not have to undersize that much. However if I can get some more comments on strength it would be nice to have the extra stroke if offset grinding to achieve the mr2 journal sizing??? I would say Daw is alot safer doing this on his l16 then I on my l6 just because I would like to run about 550 crank hp but then again with a little extra displacement maybe I wouldnt have to push the engine so hard to get that number?

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Oops, I screwed up, bending strength and stiffness will be reduced by 15%, not 12%. I was thinking 1/12*bh^3 instead of 1/4*pi*r^4 (DOH!). 15% is SIGNIFICANT. I wouldn't consider ANY reduction in journal OD, even for my engine with less than half the power you're aiming for. Like the equation says, moment of inertia varies with the FOURTH POWER of OD, so even removing a little costs a lot more in terms of strength and stiffness.

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I am a little concerned about losing strength when removing metal but there are a lot of engines running the 1.889 size journals. Unless the SR20 and 3sgte and many others are running forged cranks then I'll take the risk, especially with the L18.

 

The L24 has a 1.967" journal and the L24E has a 1.768" journal. The L24E would never stand up to any hp, but it has twice the amount of metal lost than what I am planning.

 

BTW, it looks like I can use pistons from an Acura RSX-S (K20C) in the L18 (1mm over = 86mm bore). They are compession ht. = 30mm, pin dia. = 22mm, dish vol. = 9cc. The original pin ht. = 38.1mm and the rod length of 130.2mm combined = 168.3mm. The 3sgte rod = 137.4mm and the Acura piston has a 30mm pin ht., so 167.4mm is the combined length and the offset grind to the crank journal adds another 1mm for 168.4mm and I think the L18 piston may sit slightly down in the bore as the block ht =L28, rods are same length and piston pin ht. is the same but the stroke is 1mm less in the L18 so it must sit down 0.5mm below deck stock. DAW

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Im pretty sure the 3sgte and sr20 both run forged cranks. I really would like to find a bearing that allows me to take a little less material from the datsun crankshaft my power goals are where people start having problems with the stock ld28 crank. Also where are you finding your specs for journal sizes and etc. Is there a catalog I can order to scrutinize or is it just searching for random tidbits on the net. Let me know so I can claim to be half as knowledgable as you ;)

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