7age using Honda rods???

[Mooro]

But was that just a standard grind to make sure everything is good for a rebuild? I would imagine things like knife edging/balancing and offset grinding would be more expensive but I hope you are right and it is only around the $200...it would mean 1 more piece of the puzzle fits...I'm getting more excited about the prospect of building up a 20V 7age.

[MRMOPARMAN]

yeah it was only a standard grind and linish, and the bearings. i cant imagine an offset grind costing much more. maybe a tad more for labour? balancing knife edging etc wouldbring the price up though

[DX20VT]

Well i can say I put a 4AGE piston onto one of my 7A conrods and fitted it to the 7A block,

And put a 7A piston on a 4AGE conrod and fitted it to the 4AGE block.

I can say that in both cases the top of the piston cam to exactly the same place in the bore, both down a little in the 7A and both flush with the top in the 4A.

This to me means the height form the gudeon pin to the top of the piston is exacly the same between a 4age piston and a 7A piston.

[MRMOPARMAN]

according to club4ag faq the 7a bigends are 48mm

i think datsun L16 rods with honda B18c/b18a/b16a pistons would be the go. the honda pistons come in 81.5 and 82mm, varying comp heights and dishes, 21mm pin to suit the L16 rod. the L16 rod is .5mm longer than the 7a rod, and a 52.997mm bigend, so the 7a crank would need welding.

with that combo you can get the comp super high, or turbo comp depending on what head gasket, piston dish and comp height you choose.

[RonRob]

All of this modification for a 7age. I could understand if it where a 7agte or possibly a 7agze. But as I stated in my prior post, there are many people out there running 7age's with the stock rod modified. Turning to 9K on the stock rods and road racing with this application. Furthermore my 7agze and a few others are running to this day with the stock 7a rods. Remember, the stock 7a rods are the same thickness as the 20valve black top. And to be completely honest with you, the 1 person I know who attempted to use Honda rods on club4ag about 5 years ago failed miserably.

Good luck
Ron

[JP]

it's not really the rod's that are the problem in a 7age, it's the rod bolts. The 7A rod bolts screw into the main section of the rod, they have no nut on them like the 4A rod bolts. Some people machine the 7A rods to take ARP bolts and nuts.

[Mooro]

It's not so much that the 7a rods are heaps weaker than say a blacktop rod, it's just that you are increasing the stroke by a fair bit and therefore increase piston speed and tensile loads on the rods at the same rpm, so for instance say a safe limit for a 4age rod is 8500rpm, this equates to a piston speed of 21.8m/s. A 7a rod at 7500rpm has a piston speed of 21.4m/s, so given the 7a rod is smaller than a normal 4a rod it stands to reason that 7500rpm is about right for a 7a.

As far as doing all this work for just a 7age, the peak stresses on a high compression NA motor are actually higher than those of a lower compression turbo motor. THe turbo motor will have a higher average load but generally the peak loads are lower so it is actually more critical for a 7age compared to a 7agte or 7agze.

The honda piston, L16 rod idea sounds good except that adding weld to a crank journal sounds a bit dodgey to me in terms of reliability...I would prefer the CA rod and 4a piston if it can be made to work with an offset grind.

[Mooro]

it's not really the rod's that are the problem in a 7age, it's the rod bolts. The 7A rod bolts screw into the main section of the rod, they have no nut on them like the 4A rod bolts. Some people machine the 7A rods to take ARP bolts and nuts.

Yeh I've heard varying opinions on this as to whether it is the rod or the bolting that is the problem. THe bolting maybe the first thing to let go but the rod might not be far behind. I'm still learning towards the extra security of something like a CA18 rod if it is not too difficult or expensive. If it is not feasable then I would probably still go ahead an build it with prepped 7a rods...at the end of the day it's not like a 7a bottom end is expensive or hard to come by.

[Mooro]

according to club4ag faq the 7a bigends are 48mm

Yeh I have had conflicting info on this, some say 50mm, others say 48mm. I wonder if the rod big end and the crank journal diameter gets confused...ie it stands to reason that if the crank journal is 48mm then the rod big end would be 50mm to allow you to fit a bearing shell in there.

But if anyone can clarify this for me I would appreciate it...maybe I'm the one getting confused?

[MRMOPARMAN]

i finally found a listing on CA18 rods, they are indeed the right length, but big end bore is 48mm, just like the B16a rods, so you'd need to machine down the crank journal to suit the rod

[RonRob]

it's not really the rod's that are the problem in a 7age, it's the rod bolts. The 7A rod bolts screw into the main section of the rod, they have no nut on them like the 4A rod bolts. Some people machine the 7A rods to take ARP bolts and nuts.

Now that sounds like and Excellent idea and wish I would have thought of that. Again folks, the 7a rod has been used by road racers and builders like Topi from Club4ag. He modified the stock rods to full floating ($100US) and I tell you people where reving thier 7ages to 9K with no problems. Modify the stock rod and JP's point of machining the rods to accept Arp bolts and nuts makes for a reliable 7a project in my opinion. One given from experience as our 7agze is on the road with 7a rods.

Ron

[Mooro]

There is so much conflicting info on the internet regarding 7afe rods and their strength...it's confusing

Anyway I have just been offered a complete and running CA18de engine and gearbox for free! It's almost a shame to pull down a good engine just to get a rod but it's free so I can't complain...Hmmm I wonder if a CA18de would be a better base for a build up than a 7age????? Quads, cams and increased CR..there would have to be close to 200hp on offer there

[RonRob]

Definately conflicting info on the web with regards to the 7ag. I usually find the info comes from those that are not running them and/or has never built one before.


Ron

[Mooro]

Yeh probably but I have definitely heard from some reliable sources and people who have built them that the rods fail with sustained use over 7,500rpm...It probably has a lot to do with the amount of rod prep, whether they are left press fit or fully floating, and what bolts are used...maybe if everything is done properly they would be reliable for an 8000rpm street driven/odd track work car.

[DX20VT]

maybe these can help.





Matt