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AMC 258 Build-Up

Contributed By: Brad Feick


This build up article is intended to demonstrate one approach to building an AMC 258 motor. My goals were to improve the performance of the 258 with mostly stock parts (thereby keeping the reliability), and to spend as little money as possible. I am a big believer in the fact that there is a lot of power to be extracted from a relatively stock motor, and that in my opinion, folks make "improvements" using hyped components that do nothing or even hurt performance. I will include some things I could have done as options to consider.

Part One

I started with an extremely well maintained 258 with 57K miles out of a wrecked 78 Cherokee. It sounded good while running, and combined with the condition of the truck, I knew it would be a good candidate for a refurbishing. If you are starting with a tired and abused 258, you will have to do a thorough inspection of the cylinder/piston, crank, and bearing conditions and tolerances, and have the typical block and head work done for a rebuild which I will get into later. I started by tearing down the 258 after putting it on the stand and very carefully tagging and bagging parts as they came off. In general, it is smart to put parts back in the same order and orientation as they were installed originally, especially things like lifters and pushrods if you plan to re-use them. Internal parts establish wear patterns that if swapped must re-wear to it's new mate causing problems. You can push the pushrods through a piece of cardboard or styrofoam, and store the lifters in an egg carton to keep everything in order. It's also a good idea to have a factory manual and/or parts book for reassembly. Don't fool yourself thinking you will remember it all, because chances are that you won't!

I inspected the inside of the head. The coolant passages looked good and clean, as did the combustion chambers. I would wind up cleaning up the valves along with a light lapping (yeah, I know-how did they taste?) because I wanted to replace the valve seals, and since they were out� I removed the valve springs with a small hand-held compressor. If you can beg or borrow the professional style tool that bolts to the head with a sliding bar, it will save you A LOT of time! The small compressors have a tendency to walk off of the spring which will make you go "OW!" I guarantee. It is a good idea to pre-soak the top of the spring retainer with a penetrant of some kind to break up the gunk which can make this job a real #%$@.

I chose a Fel-Pro complete engine gasket kit which comes with new nylon valve seals. The kit costs about $71 bucks at a national chain store and is a very good quality set.. Installing the seals is a snap especially if you use a little assembly lube, which can't hurt the first start up. The condition of the machined head surface was excellent, so I opted not to refinish it. The motor showed no signs of overheating. If you decide to deck the head, you might as well cut it to achieve 9:1 compression ratio. I believe that it is .060 off of a stock head, but yours may already be cut from a previous decking. (shaving a little for flatness) Your machinist will be able to determine how much has been taken if anything� With .060 off of the head, you will not experience any valve-to-piston problems, at least not with an "RV" style cam. If you are unsure, you should check the clearance. Read on.

Part Two

I sent for my cam from the land of fruits and nuts-California. I ordered direct from Crower cams when I started, so that I would have it when I was ready. Crower gave some pretty good background on cam install and degree-ing. Also sent a tube of cam lube. I considered degree-ing the cam, but decided against it when I realized that I would probably have to buy a special cam gear and bushings to accomplish that. Also, I was happy with the advertised torque and HP curves of the Crower "Baja Beast". Retarding or advancing your cam is a way to fine tune the power curves of your motor, and is worth considering if your combo (ign/intake/converter/etc) needs to have the power come on sooner or later. It's not to be taken lightly, and the stock position is usually best.

The lifters seem like quality units. They smelled like kerosene. I wonder how many manufacturers of lifters there actually are? Seems to me like you could make them on a CNC lathe... I was going to use Rhodes lifters, but after a long convo. with the tech. guy at Crower I decided to go with theirs.

Variable lifters like the Rhodes can be another way to change your cam characteristics a bit. I wasn't sure how variable lifters would affect this application, so I went with the Crower bleed-down units since they were a no-brainer, and I didn't want to "un-do" the advantages I may get with the new cam. Plus the price was right. I paid $140 bucks for the set. I didn't get springs with the cam because they were in good shape and with the low miles, I felt safe with it. If you are doing an older motor, you should get the springs. I would really love to know what the difference would be with the Rhodes on the same combo.

Anyway, the Crower "Baja Beast" (no pretension here, eh?) cam comes on @ 1K rpm which is essentially off idle to 5K rpm. I'm not looking at the spec. sheet right now but as I remember it has 280 dur. and .448 lift which I compared to the 79 factory specs- I THINK the stock cam has 243 dur. and I can't remember the lift, but it was a lot more. (real specific, huh...)

I also went with Crower because my past experiences with the "big" guys (Crane for one) is that they don't put a lot of actual research into the "off" brand engines. I mean, they sell scads of Chevy cams each year- . Do you think that they put the same effort into the relatively small number of Olds cams they sell? I seriously doubt it. Different flow characteristics in different heads require different overlap/lobe centers. Crower SEEMED to have gotten this down, but we will see won't we? Also the guy took time with me and didn't seem like "Oh great here is another wing-nut who is gonna waste my time and then buy a Crane cam". Cams seem to be an art AND a science, with no-one having the magic formulas. I have been in car clubs and watched the drag racers develop better stuff all the time. For example it seems like most guys I know are very happy with the Edelbrocks in their AMC 360s, while Lunati seems to have Buick nailed down pretty well. If I were building a 350 Chevy, I would seriously consider Crane.

The point is that you have to choose a cam based on your application and not by name. Whatever you do PLEASE do not buy a "lumpity" high RPM cam for your 258 like the ones "roundy-round" racers use in the I6 classes. You will end up hating it, and all your buddies will say "See, I told you those Jeeps bite-he used the biggest cam, and it was STILL a dog"! Cams like that are made to live in the higher RPMs. One of the 258s strengths is the fact that it makes very good torque right off of idle. Take advantage of this fact when choosing a cam.


This may amuse some of you: progress was slowed by the fact that I tried to take off the flex-plate in the bed of my J20 "Mr. Beef" so that I wouldn't bend it or that cover plate behind it while unloading it. WOW! Are those things tight or what?! I took a 1/2" breaker bar and a 3' cast-iron pipe to crack 'em loose. Well one of them was extremely obnoxious and I broke my socket. Well. Mr. Cast-Iron extension bar met Mr. Finger who was resting on Mr. Beef's bed rail probably at around 100 ft lbs. Mr. Finger really hated that and is going to lose Mr. Fingernail sooner or later... (took 7 months to heal fully)

Part Three

I wrote the following at the time I was doing the motor:

Well 258 fans-

Didn't get as far as I would've liked on the 6 this weekend, because I eyeballed the mounts on my motor stand and went to the hardware store to get grade 8 bolts to hold up the 258. Well Murphy showed up and of course I didn't get them long enough-of course a discovery I made AFTER the store was closed. RAGGUM! FRAGGUM! SNERTZ! Sifted through my 5 gal. juice bucket of bolts and came up with the right ones anyway.

The bare block is sitting on the stand now and I have 1/2 of the lifters out. I used a dental pick to fish the lifters out of the block. I also found the oil change records out of the donor Cherokee. They changed it every 3k like clockwork, and boy does it show! I can still see cross-hatching on the cylinder walls and the top of the heads looks real clean with very little scunge. The fresh oil I drained out smelled a bit like gas which I attribute to the fact that the vehicle was probably always driven with the choke on (short little hops, never got to warm up). It took 6 years for them to rack up 3k miles according to the records!!

When you are taking off the accessories and water pump/timing cover bolts, pay particular attention to which bolt goes where as there are about 4 different types.

Part Four


Got the balancer, fuel pump, lifters and cam out of the block today. Most of the lifters came out the other day, but some of them were stubborn. I went to my buddy's garage to borrow a lifter puller, but he said they break more pullers than he cares to say. They told me to just use lots of WD40 and work 'em out. He was right. It dissolved the varnish on the bottoms and out they came! I have decided to use a new timing chain since I'm in there, also because it is the bogus stock nylon type. (What possessed them to do that?)

At this point I began to make a mental list of what kind of chemicals I would need for re-assembly. Very seldom do I use the thick shmootz in a tube, even on supposedly leaky Harley projects. (I find most Harley leaks are owner-inflicted) If you use the modern chemicals in the right applications you can really end up with a fluid tight motor. RTV is not appropriate for every situation, like oil pumps where tolerances could be affected by using RTV. I like to use High Tack in situations like that.

Anyway, tomorrow I'll loosen the main caps and inspect the bearings/replace the rear seal and take the wire wheel to the oil pan and loosen the scale to get ready for paint. I'm gonna clean the lifter galley a bit and then I'll put in the cam and lifters. Then on with the pan, timing cover, etc. It's beginning to look a lot like xmas...

Part Four and a Half

If you are starting with a beat-up 258 you will not have to manually clean the block out like I did mainly because you will most likely strip it and get it cooked out at the machine shop. Speaking of which, you can save yourself a lot of money by doing the inspection of the block and bottom end yourself. If you have a service manual, you can check the tolerances of the cyl/crank/pistons/etc. and decide whether you can just lightly hone the cylinders and use new rings , or if you have to have a complete bore with new pistons. Naturally, it is better to start with all new machining and parts, but sometimes it is cost prohibitive. Regardless of what the purists may tell you, if your crank is not scored and the cylinders look OK and are within runout tolerance, it is legitimate to just deglaze the cylinders and use new iron rings(which conform better to an old surface) and bearings. Most of us are not going to be drag racing the 258 (are ANY of us??) so given the rusty state of most of the Full Size Jeeps, a refreshed 258 will probably last until you are ready to sweep the truck into a box.

Today I picked up the all-steel timing gear for the 258. It's a beautiful thing. The one thing that I noticed is that on both the nylon AND the steel, there is no provision for a bushing for the cam which means that there is no way to degree the cam in the 258 unless one buys a special gear. Well folks that ain't happenin'. I have faith that the steel gear will be accurate and consistent enough. Let's keep in mind that stock motors run for MUCHO miles and don't come apart (unless you beat and neglect them) granted, not with the performance I expect here, but the point is that I'm not going to lengths to degree this motor. If it all were right in front of me I'd do it, but it aint.

Well it would seem that I'm done playing scrape master, so tomorrow looks to be the day the put-back gets under way. So far the costs have been:

Motor with 57K miles-$125
Cam+lifters- $140
Gasket set- (full) $71
Timing set- $40(?)
Motor mounts- $(?)
Misc. Goo- $20(?)

There are a lot of things I didn't list in the costs that you should not take for granted. Common sense stuff to replace when redoing a motor really add up. Do NOT underestimate them if you are on a budget. Remember belts/hoses/coolant/clamps/filters/oil/plugs/ign stuff/etc. I spent around $400 to just refurbish this 258 WITHOUT getting into the bottom end.

Part Five

Hi guys-

I am beginning to assemble the 258, and thus far have run into few potential problems. I started the reassembly by removing the rear main bearing cap and replacing the rear main seal. It helps to loosen all the bearing caps and lightly lift up on the crank to get the upper seal slipped around. Otherwise the block starts "shaving" the seal on the outer side of the seal. BTW-I followed the shop manual to the letter on the rear main seal install it went great. I then re-torqued all of the bearing caps and connecting rods to the factory in-service specs. I then took the cover off of the oil pump and inspected the gears-looked great with normal wear marks. I forced some break-in supplement into the pump and up into the block, so the pump forces that through everything first. I then coated all the contact and wear areas with break-in lube and reassembled the cover gasket with a light coating of Hi-Tack and torqued all oil-pump related fasteners.

BTW- at this point I began playing with the pan seals and although not specifically addressed in the manual, it looks like the proper order of assembly with re. to the seals is as follows: inner rear main bearing cap (lower) seal flush with block/cork pan seal tabs set on top of lower seal tabs/outer rear main cap to pan seal set on top of cork tabs.

It looks like RTV at the junctions just mentioned would be the way to go, with Hi-Tack brushed on to the cork gaskets prior to placing them on the block. Anyway I'm getting ahead of myself-just fitting the gaskets and making a plan. I'm going to insert the cam next time with the pan off in order to support it while threading it through the block so that I don't nick the bearings or cam.

Part Six

OK! The project is starting to come together as I am getting into the reassembly. I forgot to mention last time that before I put the oil pump cover on, I packed the pump with Vaseline. Also on the subject of replacing the pan gasket I should have gone one step further and said that the point is I feel it would be better to get the rubber seal that rides in the bearing cap groove as well as the cork gaskets when doing a pan-drop type repair.

Anyway-in the interests of cleanliness I had already cleaned what little sludge and deposits there were in the hiding spots in the block. I have also torqued all lower end connectors/cleaned gasket surfaces/etc. While the block was flipped upside down I cleaned the cam bearings and coated them with assembly lube, coated the cam with the same and installed the cam making sure not to nick it. While upside down you can support the cam while threading it through the block. At this point I prepped the oil pan by scraping the sludge out and running it on the wire wheel in preparation for the coat of AMC blue. I installed the gaskets, evenly torqued the pan down and flipped it over in order to install the lifters. In case it hasn't occurred to you, don't flip the block over with the new lifters in it-they don't have varnish on them and will probably fall out and you will hate that.

I soaked my lifters overnight in break-in lube (there are many schools of thought on lifter prep), wiped them off and coated them in assembly lube. They slip right in no problem. Hmmm! Excitement is growing as it am lookin' like this thing might just run again. I'm going to stop here so I can get this out, the next post will be on the head prep and valve seals/de-coking (as the Brits say) et al. In the meantime it's on to the dreaded wire wheel to clean up all of the remaining fasteners in order to prepare for the final stages of assembly. That's all for now-

Part Seven

There is an excellent article on valve seal replacement done by_________ which can be viewed on the IFSJA web site. Because of this I will not duplicate______'s fine effort here.

I will however add that I used a K-D claw-style spring compressor, and I did the valves with the head removed and had no problems. One advantage to replacing valve seals with the head off is that you can lap the valves and de-gunk the chamber while you're at it. I carefully wire wheeled the deposits off of the valves and buffed them out before I lightly cleaned up the seats with a stick and compound just to ensure they were seating correctly. I was very careful not to 'wheel the seating surface of the valves, just the tops and on the stem bottoms. After starting with the rough compound, the valves and seats looked like a dull gray. I eventually made the seating faces much shinier with the fine compound. I made very sure to clean the lapping compound from out of the runners because you don't want to lap your valve guides for the next 100K miles. After cleaning everything up I re-assembled the head with new seals and break-in lube. I also made sure to put everything back from whence it came due to the established wear patterns.

At this point I was nearly ready to torque down the head, so I tapped all of the threaded bosses in the head and cleaned up the fasteners (MORE wire wheel) and blew out the passages in the head. BTW my cloth/wire wheel motor was a yard sale (washing machine) item I picked up for a couple of bucks and hold to the bench with 2 vice grips. I wiped and blew out the cylinders before wiping the walls with break-in lube for a smoky puff of insurance.

I torqued the head back on in accordance with the factory manual in re. to pattern of tightening, but I make it a practice to sneak up on the torque figure in thirds of the total in order to get a better more uniform seal. Man! It looks like it could run soon! Next I will be messing with the exhaust/intake assembly which I have been spraying with Liquid Wrench for weeks now so I have a fair chance at no snappage. I think I will use the exhaust gasket supplied with the kit, because it seems like a real good idea to me. I *MAY* also rebuild the carb esp. if I can dig up any upgrades to do to a stock BBD. Or, I may start reviewing my carb basics in my excellent "Rochester QuadraJet" book that I learned a lot from and apply it to Mr. Carter. There is good tech article on Off-Road.Com on how to cure common BBD woes.

Part Eight

I think the last post on this topic was back in March, but that was before my truck developed an appetite for transmissions. Well here we are in November ('97) and I finally found the time to finish the 258. The last part on the web site was where I torqued down the head so I will take it from there.

When I tore the 258 down, I made sure to put my pushrods through a piece of styrofoam so that they would stay in order for re-assembly. As I dropped the pushrods back into place, I made sure that they were thoroughly coated on the ends with assembly lube. After checking to see if they were seated on the lifter and in the rocker correctly, I tightened the rocker bolts to the factory spec. When I tore down the motor, I was surprised to find that the valve cover had no gasket, but had copious amounts of RTV gripping the cover like grim death. Hey- it obviously worked since the block was clean. I however wanted to try the gasket, so I had already been working with a tube of that copper RTV, so I figured I'd try it, since re-doing it is not hard at all, esp. on this motor in a truck. I RTV'd the gasket to the head, let it cure a bit and then RTV'd the top of the gasket and put the cover into place. When I torqued the cover down, I wiped the excess RTV back into the head/gasket/cover to really get a good seal. One word of caution here-even though I knew this as I was doing it, I still over tightened the cover and kinda sucked the gasket back under the cover a bit. I used enough RTV that it shouldn't matter, but the point is that you don't have to go Herc. on the cover as it will push the gasket around.

I then flipped the motor over on the stand and had a look-see at the oil pan situation. I ended up cleaning the gasket surface on both the oil pan and the valve cover with a wire wheel. This works great and removes RTV in a snap as opposed to scraping your brains out with a blade. BTW, I remember using Scotch Brite to prep the head/block mating surfaces. To replace the oil pan, it's probably a good idea to put the timing cover on first, so I drove the crank seal out from the back by catching the edge of the seal with a screwdriver. There is a relief cut into the cover for this purpose. I reinstalled the seal with High Tack around the circumference and pressed it in with a vice and a 1 3/4" socket which fit the OD of the seal perfectly. I went back to the block and scraped the cover gasket which-I mean you wanna talk about gorilla snot, OK maybe not...

Using High-Tack, I positioned the gasket onto the block, waited for it to dry and torqued down my wire-wheeled bolts that I slathered in a Permatex goo that's made for bolts going into the water jacket. I noticed at this point that my cam was not perfectly aligned with the lifters, so I called Crower, and they told me that this is the way that the cam-to-lifter relationship should look. Before I talk about assembling the oil pan I should mention that there seems to be several different schools of thought on gasket prep. and the use of RTV and other schmutz. Some guys recommend using NO goo at all, and in some applications I think that this is smart. (Like tight clearance pumps and such) I have heard of for example soaking a tranny pan gasket in ATF before the install so that the gasket is swelled and won't wick anymore fluid. I think that you have to assess the situation for yourself and use your best judgement.

I ended up using High-Tack on the cork gaskets and a little RTV at the gasket unions. I also used a bit of High-Tack on the rubber timing cover to oil pan seal. After I torqued the oil pan to factory spec., I flipped the motor over and began to prep the block for the manifolds, fuel pump, and accessories. I didn't actually mount the accessories on the front of the motor in the end because I still have to move it out of my basement, and I don't want any of my biker buddies using the distributor or whatever for a hand hold. In fact, I have two rough cut oak beams that I am going to drill so that four of us can carry out and up the steps safari-style.

Part Nine

I would like to end this article with some options to extract some very cheap power out of your 258 (and any motor for that matter) while retaining and actually adding reliability. The first thing I would like to mention is the practice of gasket matching. This is where you cut away excess casting off of your head and intake to match the size of the gasket in between them. You do this by putting machinists dye on the head and intake and scribing the inside circumference of the gasket hole when mounted in place. You then grind away up to your mark with a high speed die grinder. What this does is allows your motor to breathe easier without hitting rough edges which introduces unwanted swirl in the chambers, not to mention enlarging the ports. It is advisable to practice on a junk head to get the feel of how fast the cast iron cuts with the grinder.

The second and probably cheapest and best improvement that can be made to the 258 is to add an HEI distributor out of a Chevy straight six. If you swap the gear off of your 258 distributor, it drops right in! The stock Motorcrap ignition is actually pretty pathetic, and is a cause of hard starting and bad idling. It is hard to beat the HEI, even for a lot more money. Your 258 will not even approach the upper RPM limits of the HEI. FSJ guys with the 350 Buick can benefit from this mod as well. Sorry 360 guys, you'll have to go with the Jacobs Omni or similar ignition. (I did this on my 360, and to date it was the BEST thing that ever happened to it!) There are excellent articles on the HEI conversion on Off-Road.Com, And Jacobs install on the IFSJA sites. To further bullet proof the HEI, you can remove the stock module and use the Chrysler style amplifier (Standard Ignition part # LX101). There are schematics for this on the IFSJA site as well.

A note on the stock BBD- the Carters get I believe an undeserved bad rap. Carbs are probably the most toyed with and least understood engine component. Usually, a BBD with 100K + miles gets yanked in favor of a brand new Holley or Weber. When the motor runs better after the swap, guys trash the BBD! Well, can you imagine that?! A new carb runs better than one with 100K miles! Amazing, huh? I think that the Weber truly IS a better carb than the BBD, but before you spend money on a new carb that might have gone into better main bearings (I recommend Clevite 77s), maybe you should rebuild the stock carb using a quality kit and good rebuilding practices. You can easily bolt the Weber on later.

Part Ten

I have since sold the 258 to a buddy who is installing the motor in a J10 as of late summer 98. I have moved on to a 455 Buick project for my J20. I will detail the performance of the 258 as soon as the install is completed. Stay tuned.

Brad Feick

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