t.mcginley.jr

Hi all,

I have a 4.0 with unknown mileage (was told 90k), that I tried to do a leakdown test on. I can't get a good reading on cylinders 2,3, or 4, either from not being able to find TDC or just leaking valves.

If I lap all the valves or buy new ones and lap them in, the hydraulic lifters should make up the difference (lash) correct? I know there are tolerances for valve seats, pushrod travel, etc. but with just lapping to get the valve seats smooth again shouldn't hurt too much.

Any input would be great. It's an 0630 head by the way, I was told the engine is a 98 or 99.

Jeep Driver

You won't effect lash by lapping the valves.

t.mcginley.jr

Ok cool that's what I thought. Do valve springs in these heads usually wear out?

Waynerd

I'm having an issue with cylinder 1 not holding more than 10lbs where as the other cylinders will hold 40lbs. I've done some research and from what I found the valve springs had been redesigned using a thinner diameter wire and prone to breaking or weakening severely. There's also some technical service bulletin about rotating the valves but I don't remember which years that applied to. I haven't pulled the valve cover yet but I'm getting a misfire in cylinder 1 and I'm expecting to find an issue with the spring or springs. Hopefully it's that simple.

Jeep Driver

Mellings valve springs are cheap........like $6 each IIRC.


Replace them.

Jeep Driver

https://www.summitracing.com/parts/s...798b/overview/


Here, $2 each........you cannot afford to not replace them.