[Oily]

From this thread.

Originally Posted by gotCLAY

Any know what size push rod go into a 1986 258?

Originally Posted by Fjguercio

This is a common problem and an engine builder put too long a push rod in my engine ...

Originally Posted by Old4X

......I forgot about what short pushrods would do.
......probably less likely than the pushrod mixup.

Originally Posted by gotCLAY

Ok found out that my push rods where to short.

Originally Posted by Fjguercio

.....I went from Napa, ORileys and all over town. Every push rod length was differenet and they did not have much to offer. I was able to get a book photocopy of a few pages that list the years and length and the part numbers. Are others out there still having this problem?

I might have wrong sized push rods. Anyone know where we can get the correct specs?
Gee, you would think the tried and true 4.2 would be uniform. The date code on my block is 10/15/00. Not sure when the head was manufactured or if it was originally on my block. I guess if they shave the head deck it would affect it too.
Anymore insight on this subject ?

[Oily]

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ten characters.

[starfire340]

I had a bent one in my 83 when I bought it. Evidently there is (was) a vintage service bulletin floating around from AMC about this. I think it involved using longer rods to replace the bad one(s). It seems to me my local parts store had both lengths listed, but I am not sure which is the proper one. It seems to me I replaced the bad one with the longer version and simply adjusted the valve according to std specs and have had no other issues with it in a year....You might try contacting a Chrysler dealer, they should have the bulletin available?
Good Luck!

[Oily]

Thanks starfire.

Originally Posted by starfire340

It seems to me I replaced the bad one with the longer version and simply adjusted the valve according to std specs......

It would seem that a longer one would be too tight and bend. Then again, I can see one too short bouncing around getting bent also.
Should be no valve adjustment with hydraulic lifters.

[starfire340]

I understand what you are saying, but we are talking thousanths here, barely perceptible except when laid side by side. What I meant to say instead of "adjusting" valves was "torquing rocker fasteners'. That was the whole point of the longer pushrod was because of them popping out....I would still try to google info on this, will probably clear it up for you.

[Fjguercio]

Oily,
Sorry it took me a little bit to put this together. I am going to ask Admin to make this a stick or Tech Article.

Hope it helps,
Fred



Push Rod length seems to vary all over the place when I purchased them for 1978 CJ7 with 258. I found the year of AMC Engine and the vendor you get the push rod from can make a huge difference in length. Wrong length can cause engine failure or poor operation.

Every push rod length was different and they did not have much to offer. Examples: Red Rooster 9.622 & 9.594”, ORiley 9.622”, Checker none, Napa 9.65”, CarQuest 9.594”. These are the offering for my 1978 Engine and some too long or short.

I was able to get a photo copies of a few pages that list the years and length and the part numbers. The pages were from an old Melling Parts Book. Pioneer Inc, 601-483-5211, Meridian, MS, was the company that had the correct information and the correct push rods. They were very helpful.

The copies I have are very poor so I cannot post them.

The Engine Remanufacture installed incorrect push rods and caused a total engine failure so this does happen. The Push Rods were too long by, .12”, a lot considering lifters can take up .030” of play with hydraulic oil pressure. The LONG incorrect push rods (9.62” correct vs 9.74” installed) and bent push rod, collapsed lifter. one lifter out of pocket, and oil path problem took out the #1 connect rod bearing. They sent me a set of push rods to replace the bent one and they were the correct length, 9.62. Glad I measured the push rods with a 12” digital caliper and took pictures. Engine Remanufacture tried to blame me for the engine failure claiming detonation. Money was refunded in full.

Glad I did the research it saved my but. They wanted $1000 to put the engine back together & return shipping & my warranty now void of any claims.

I am pretty sure many of us here at JeepForum have issue with push rods and may not be aware. Non Stock cams can / will affect your valve train geometry and parts used.


This information was from an old Melling Parts Listing for AMC Engines 258 or the 4.2 liter

PUSH RODS AMC 258 4.2 liter stock cam & set up

MPR-301 9.594” x 5/16 1971-1974 w/o Rocker Arm Shaft
MRP-332 9.658” x 5/16 1971-1974 w/ Rocker Arm Shaft (BB ends)
MPR-301 9.594” x 5/16 1975-1976
MPR-301 9.594” x 5/16 1977 w/ Temp Sending Unit in front of engine
MPR-333 9.622” x 5/16 1977 w/ Temp Sending Unit in rear of engine
MPR-333 9.622” x 5/16 1978-1980
MPR-353 9.700” x 5/16 1981-1988



Rocker Arms AMC 258 4.2 liter stock cam & set up

MR-812 1971-1974 use w/ engines with rocker arm shaft
MR-801 1974-1982 use w/ engines with rocker arm and individual pivots
MR-740 1983-1990

[Oily]

Originally Posted by Fjguercio

Oily,
Sorry it took me a little bit to put this together.

You did good. Very good. Thanks, from all of us.

Originally Posted by OCDWheeler

....as far as the "tick is normal in 258's" I hate hearing that......I've read that its "normal" on forums quite a bit but It just can't be normal can it? .....

How normal (loud) is normal? I never did like to hear that either.

[Fjguercio]

Thanks Oily,

Fred