Help! doing the 4.0 head swap on a 258!

Or use a flashlight to sight and seat them.

Strange.

Oh, TDC just means top dead center and yes, the piston does come up to TDC twice in one engine cycle. That is why it is a 4 stroke engine, not a 2 stroke.

When it is on the compression stroke TDC, the valves are closed and the rotor is pointing at #1 plug wire with the crank at 0. When it is on the exhaust/intake stroke, some air will still come out the plug hole as the piston comes up to TDC and the valves will be open. The piston is up top and the crank reads 0 degrees again.

You need to block the plug hole with your finger to feel for compression or remove the distributor cap to make sure it is on TDC #1 on the compression stroke or every valve you check will be open.

Mike

Harris Family wrote:

Mike, Not trying to be an ass. Just a bit frustrated by my situation. Sorry to take it out on you guys. I did check the rotor position and its where it should be. I've been over it a dozn times and the only explanation I can com up with is that I decked the block .010 last year during a rebuild, and the head is a reman. It probably has been surfaced as well as new valves and ground seats. Ground seats would raise the valve stems higher block decking and head machining would put the rocker bosses anywhere between .020 and god knows how much closer to the tops of the lifters. Add it all up and something has to change to compensate. I fugure its got to be the pushrods. I've read every article and thread I can mine off the internet and all except one says the rockers are interchangeable. All except another say the rods are interchangeable. The one exception says his situation was exactly like mine. As a side note I contacted the guy who had pushrod problems and he was told by HESCO, who he got his head from, to put washers under the rocker pivots to compensate for the difference. While it surely would be the cheapest fix, as he said it is pretty "Mickey Mouse". Not to mention the stress put on the rocker bosses. I guess I was looking more for someone to say "yep I had the same problem and this is what I had to do". Not that I don't appreciate the advice you guys throw out here, because I really do. You guys are my fifth shop manual, and I really appreciate it. Rich Harris

1986 (mostly) CJ7. Detroits F/R 4:10s, 33x12.50 BFG MT's, onepiece axles, revolver shackles, Rubicon Express 2.5" Wrangler lift, Procomp MX6 shocks (way out perform RS900's BTW), Custom Swingout tirecarrier bumper, and more...

"Mike Romain" wrote in message news: snipped-for-privacy@sympatico.ca...

This only works when the cam timing is correct.....and isnt that what were trying to find out ????

Harris Family wrote: > The crankshaft can go to 0

If not, the cam timing is wrong !!!!!!

no

Ageed

4.0l rods are 1mm shorter, but that's not enough for my problem.

Wow. That's a drag.

Well that sounds more like you just plain got old worn out parts painted up pretty.

Heads can only be 'rebuilt' so many times and then they are garbage. Yours sound like it has passed over the point of usefulness.

Yours is obviously way out of spec and I can't see any 'improved' performance happening out of a dead head.

The valve timing will not match up with the crank using different stroke rods and lifters. You will 'really' have to watch the adjustment or the first time you red line it accidentally or on purpose you will punch valves through the pistons. Are you going to use the heavy double spring setup to hold the valves from floating?

'I' personally would not use a head that has worn enough to need custom lifters and rods.

Good luck!

Mike

Harris Family wrote:

When the valves hit the piston you better be 200% sure to check the timing so a simple "no" doesnt fix it

Also, there are thicker metal headgaskets for sale that might work with the shortest pushrods. A friend of mine used them on his chevy engine to avoid using race gasoline. not the best fix but it might work for now.

Johan

Harris Family wrote:

I read your Reply to Mike, and I can't see that the machine work would be causing the problems yo uare having either.

Something silly is wrong.

I suggested earlier that you might have issues with the timing chain, but I think you said the timing chain has not been altered, so I assume that means the cam is the same and has not been changed.

The only other thing I can think of is that the bosses for the rocker arms on the 4.0 are taller than for the 4.2. This would leave the rockers lower, and they would hit the valves sooner and send the opposite end even closer to the cam, making the pushrods way too long, which seems to be your complaint. If this were the case, washers under the bosses would be a reasonable fix. Well, maybe washers are too low tech, but you need some way to space the entire rocker arm assembly further from the top of the head. I think Hesco's advice is not too far off from what you need, else you need to investigate the bosses that hold the rockers up.

Too bad... :-(

Mike

Harris Family wrote:

Don't think the 258 or 242 are interference engines.

While that may be on a stock setup, when the valves are opening too far, factory specs are tossed out the window.

I mean does anyone know by how many thousands the piston clears the valve?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Dave Milne wrote: