2000$ recipe for 401 rebuild including machine work?

roadgrime

welp my 401 is toast # cylinder broke the rings and piston. i caught it early and there isnt any real scoring in the piston not even enough to hook a finger nail on. but i got to get the rig back on the road. its in a 79 wt so obviously i am more concerned with low end for my days of wheeling. i have a holley dominator intake and edelbrock 1406 at the least i am thinking new cam and i know i ned pistons. so what do you recomend for a good reliable rebuild with a dollar limit of around 2000? part numbers vendors websites all are welcome so i can research what you are saying.

tufcj

I rebuilt my AMX 390 for around $2500. That included bore, balance, turn crank, new rings, bearings, FORGED pistons, new cam and lifters, and valve jobs on the heads including a mild port/polish. I did all the assembly myself.

I got a lot of the parts from www.fastengineparts.com (Mad Dog Racing). If you call them, ask for D.W. at x-113, he can point you in the right direction on a lot of AMC parts.

First thing I'd do is scrap that Holley intake. They're just too restrictive for a good breathing 401. Go to an Edelbrock performer or air-gap.

Bob
tufcj

roadgrime

well a little background on what went on with the motor. at christmas i got the oil pump mid plate from bulltear and put that in while redoing all the gaskets and seals on the front main timing cover etc. adjusted the timing and every thing seemed real good. i drove the rig 600 miles home with no issues and it ran real good. about 3 days later i notices substantial amounts of oil all over the top of the engine blowing out the breater valve and a very slight miss. i tweaked the timing and carb a bit and while it ran better i still wasnt happy with it. i drove it about 10 miles and notices i had lost alot of power. got the rig home and of course i had no compression on the #3 cylinder. so i parked it. this weekend i pulled the head off andi noticed that i on all the sylinders i could see the rings there was that large a gap between the piston and the cylinder wall. and then i notices i was missing about 2 in of ring on the #3 cylinder. after pulling the piston i found the rings had folded in on the piston breaking the lands. it didnt score the piston. its one of those supposedly rebuilt engines from the PO with maybe 20,000 miles on it so i am guessing all they did is slap a hone job and throw in new rings or possibly they went .010 over and used the same pistons with new rings judging by the gap i see between the piston and wall? I am going to have to look up some specs on the Z series holley intake as I hear from some it suck and others that its great so if anyone has any hard data i would like to see it. as for the rebuild i think i would like to get the comprssion up to 9-9.5 and then probably look at a cam. I dont see any stamps on the piston so i am thinking i might be able to take it to .020 -.030 over . nothing radical just a good solid reliable runner

tufcj

My buddy bought a Ford pickup with a remanned engine in it. It had this annoying tick that we couldn't find. We finally pulled the motor and disassembled it, and found that it had been bored .030", and had standard pistons in it. This thing had been driven that way for over 10K miles. We miked the bores for round and taper, and they were still in spec, so we honed it, dropped in .030 pistons and new rings, and he still drives it daily. A lot of time when a ring land breaks, it's a sign of severe detonation. are there any "dings" int the tops of the pistons, like something had bounced around in there? That's also a sign. I would get out a set of calipers, size the bore and piston, and see the difference. There should be only around .004-.005 piston to wall clearance, some are built a bit sloppier. If you can see the ring past the piston, somethings surely wrong. Bob tufcj

roadgrime

I cant see anything that would indicate detonation other than the broken rings and i was fairly religious in checking adjust timing if i thought i heard any "pinging" which wasnt often, as near as i can tell the only two ways to know for sure if it is detonation instead of pre ignition is to run a knock sensor tune to 6400 htz or to monitor the exhaust gas temps (temps will drop when its detonating) i dont see any dents in the top of the piston as you mentioned and the only other symptom i know to look for would be cracked spark plugs wich i didnt have either. as for the tollerance using my feeler guages i have about .030 gap between the top of the piston(inboard towards intake)and wall on the top of the piston and .010 on the bottom (outboard to outside the block)

Rogue Racer

Another cause of broken ring lands can be excessive ring to land clearance in combination with excessive piston to bore clearance, which sounds reasonable and consistent with the evidence you have given. If their idea of a "rebuild" was to hone it to get rid of a top ring groove, run a ring groove cleaner around the pistons to get rid of carbon buildup and then throw a cheapy set of cast rings in it, it wouldn't take much to create the situation you describe, especially if they only honed it with a dingleberry type hone and did not take the taper out of it. If you can get a .010" feeler guage between the skirt of the piston and the cylinder wall that's way too much clearance for a stock cast piston. Forget those pistons and plan on a new set with an overbore. Forged low compression pistons (SpeedPro L2380F) can be had for around $400 and would be well worth the money. Other choices are the Ross pistons from www.fastengineparts.com ($599) or the Wiseco pistons from www.flatlanderracing.com ($629). In either case, use moly rings and take your time rebuilding to make sure everything is right. Oh, and use one of MC's front covers - well worth the money for the perfromance and piece of mind.

Rogue Racer

I left this off the revious message. I heartily agree that the manifold of choice here would be the Edelbrock over the Holley. The Edelbrock Performer or AirGap will give a smoother power curve and less sensitivity to changing conditions. The Performer will not make as much power as the AirGap will, but will give a bit more grunt on the extreme bottom end (under 2000 rpm). There are many good camshafts out there, just remember to stay in the under 215 degrees at .050" range. I would look at an Engle K-52HYD cam. It is short (209 degrees at .050") so the idle quality should be good; it has fast ramps and good lift (.489") but not so much that you would have to do major modifications to the valve train or worry about piston to valve clearance. It comes ground on 112 degree lobe separation (would be nice to get 110 or 108) and would probably work best installed at 106 or 108. One final thing, take the time to do what ever to calculate exact compression ratio, even if you have to pay somebody to CC a few combustion chambers. If you need help with this, email me and I will step you through the process. Too often I have seen engines that do not perform up to expectations due to incredibly low compression ratios. People assume when a piston is advertised as a "8.5 to 1" or whatever, that their engine really has that.

roadgrime

I looked at the air gap but i seem to remember that its range is 2500-5500 and since this is a heavy 4x4 i want to get as much grunt in the low end as possible even if it means sacrificing some of the top end. as for the CC i am currently trying to figure out what dish head I have (since i cant find numbers stamped anywhere) as I know the volume of the head will have alot to do with my CC. i will probably drop you a line as i begin to work through the numbers on what i should expect and start deciding on parts.

tufcj

The casting number on the head is on top, between the number 1-2 or 3-4 valves, you have to pull the valve cover. It will start with a 319, 321, 322,or 323. But basically, unless you have a rare set of 1970 heads with the casting # 3196291-C, they'll be 58 CC. The 1970-1974 heads have Chevy style rockers, the 1975-up have the bridged style rockers. Bob tufcj

roadgrime

well i have the head off the engine so i will take a look tonight since i have the bridged rockers I am assuming either 75-76 since i think 76 was the last year of the 401 in the FSJ? unless it came out of something else?

jeepsr4ever

could be up to a 78 or even a titled 79' with a 401...seen that too. Good luck

Dusty

roadgrime wrote
I looked at the air gap but i seem to remember that its range is 2500-5500 and since this is a heavy 4x4 i want to get as much grunt in the low end as possible even if it means sacrificing some of the top end.

as for the CC i am currently trying to figure out what dish head I have (since i cant find numbers stamped anywhere) as I know the volume of the head will have alot to do with my CC. i will probably drop you a line as i begin to work through the numbers on what i should expect and start deciding on parts.

they say 2500-5500 but it works really well all across the board and as to low end grunt the 401 has plenty so you can deter a little from common practice and sneak a few extra RPMS and HP into the picture without really loosing much if any noticable low end torque and crawlability. Most of the guys in our AMC powered group of jeeps either run the R2B edelbrock intake or the Airgap with one outcast running the torker. I agree with the above statement the holley is not a good intake, its like applying SB chevy or ford engine build techniques to a Big block hemi or an AMC :mrgreen:. (im visualizing a cocktail straw and a regular milkshake straw that poor 401 will be wheazing by 3500) :mrgreen:

Mad dog is selling that TRW 9.8 forged piston engine rebuild kit for something like 750 i think thats what i saw for a price anyways, the machinework and balancing on mine was 1600 minus the heads which would have been in the 700 ballpark but if i had shopped it around probably could have found a better deal. I leaned towards the Howards cam .479 lift 292 duration 222@ .50" on a 114 lobe. have seen and riden in one other 401 built with this cam and it idled well crawled really well had a fairly flat torque curve, pulled hard though and was really street friendly and that was with 9.7:1 compression and it had that sound to it that let you know it wasnt stock. my compression ratio with aluminium heads is 10.17:1 and i am using that cam with fuel injection. that same cam in a 10:1 360 was too much almost a gutless wonder off idle in a trail rig that came alive too late.

Becareful with the 401 not to cut yourself off at the nuts, i like being able to spin up to 6000 rpm when i want to and still being able to idle over rocks, the 401 offers that versatility too many people dont build em to take advantage of thier full potential. It's a long winded motor so let her breath, amazingly enough the torque sticks around on the dyno in the low rpms even when you bump the stick up quite a bit.

I want to say another 401 combo that a friend of mine is running in his CJ5 crawler is a 280H comp stick with .480 lift with 108 lobe, might be the 270H but anyways with 9.8:1 compression, airgap and 750 holley off road carb and DUI distributor. T-18 dana 20 and 3.73's on 33's and it has no problem idling over and up anything the rubicon or Moab has had to offerand yet is an animal out on the road and the sand dunes. It has a mild lope and lets you know its mean but it doesnt effect it at on on the trail.

And for your choice in intakes, on guy in our group has run a torker intake for forever 3000-7000rpm intake or what ever it is on stock 360's and a stock 304 and that thing has never seemed to effect those engines in his rock crawler.

The point of this long post is AMC like to work differently than many people expect. keep that in mind while choosing parts and pieces.

happy trails

roadgrime

is the issue with the holley the size of the runners where they go into the heads? since i pulled the intake and heads i have been admiring the fact that the holley runners are half the size of that the heads seem to be able to take. has anyone tried running the die grinder on the holley to open up the runners or are we saying its a lost cause. i have no quams about about opening up the runners having done many port jobs on heads but i would like to hear if there is any reason not to do this. Finally got around to looking at the heads and the number is3220502-1 so according to the chart on this forum it shows to be a 74 head. otherwise great information coming from you guys!

Rogue Racer

Don't waste your time trying to make the Holley into something it will never be. The 502 head is a good head. Don't take for granted that the combustion chamber volume is whatever common conversation says corresponds to the casting number. I have CC'd too many combustion chambers that were not close to what specs say. Spend the money to have them measured so you will not be surprised or in the dark.