xj-grin
NAXJA Member #1096
- Location
- Colorado Springs, Colorado
So, long story short: Coming back from Moab last month, I noticed a marked reduction in power in the XJ, like it would barely hold 60 up the passes in 4th gear. So, once home and hosed off, I brought her into the garage for some diagnostics, finger crossing, and general karma searching.
Specs: 1999 XJ, 4.6L stoker built with an accurate power kit, notorious Crane cam, solid lifters, stock valve train with heavier springs. 91k miles -- not bad for a stroker regardless.
Step 1 - compression check: 130lbs all around, except for 110 on #2, and 120 on #6. Even 130 is fairly low for a 9.5-1 stroker motor, although OK for one with this many miles. Time to pull the head.
Step 2 - head pulled, and FrankZ and I do an inspection and a couple of leak tests -- several cylinders, notably #2 and #6, but a little bit on all of them have leakage at the valves, indicating a valve job would be in order at a minimum, but unfortunately, that is not all...
The leakage in #2 is so severe that it is very likely it has not been providing combustion in any material way for a while (I had noticed a drop in performance before Utah, but figured my Butt-Dyno was just out of calibration)... Important to note that the cylinder walls in #6 are a bit glazed, and the carbon is cooked off the piston, indicating some steam-cleaning going on that shouldn't be.
FrankZ, being the gentleman and scholar that he is, brought over a fairly fresh head that he had lying around, if nothing else for comparative purposes, although that turns out not to be the case. Interesting that my head, an 0630 casting, is significantly different from Frank's, also a 0630 casting, although an earlier one. The water jacket outlets behind cylinder #6 on my head are roughly 1/4 inch from the combustion chamber, and are overlapping a little with the contact area for the head gasket:
Franks are a full 1/8 inch further away from the combustion chamber:
It appears that some coolant, for whatever reason, was sneaking by this weakpoint, and soaking #6 -- it may or may not have been firing, and certainly wasn't providing much in the way of oommph.
There also was a visible crack in the head at the center water jacket outlet, although it did not appear that any coolant had been making it into the #3 or 4 chambers just yet:
The original valve job on this head was not particularly stellar, although given that it put out 90K, I guess I can't bitch too much. Notice how the valve in combustion chamber #3 is so fully seated that there is no margin within the combustion chamber at all, compared to chamber #4 below it:
SOOOOO, I have re-honed the cylinders, put the heavy valves onto my newly acquired head from Frank (muchas gracias, brother, send me a bill), and will start reassembly this week. Oh, and I found a long-suspected exhaust leak in the notorious header junction, so I'll be throwing an APN header on there while I'm at it. Lessons learned: (1)quality control in chrysler head castings leaves a bit to be desired; (2) the 4.0 (and variants) will run for a long time with a piss-poor head; (3) a 4.6 stroker will run tolerably well on 4-5 cylinders; and (4) Frank is da man.
eace:
Specs: 1999 XJ, 4.6L stoker built with an accurate power kit, notorious Crane cam, solid lifters, stock valve train with heavier springs. 91k miles -- not bad for a stroker regardless.
Step 1 - compression check: 130lbs all around, except for 110 on #2, and 120 on #6. Even 130 is fairly low for a 9.5-1 stroker motor, although OK for one with this many miles. Time to pull the head.
Step 2 - head pulled, and FrankZ and I do an inspection and a couple of leak tests -- several cylinders, notably #2 and #6, but a little bit on all of them have leakage at the valves, indicating a valve job would be in order at a minimum, but unfortunately, that is not all...
The leakage in #2 is so severe that it is very likely it has not been providing combustion in any material way for a while (I had noticed a drop in performance before Utah, but figured my Butt-Dyno was just out of calibration)... Important to note that the cylinder walls in #6 are a bit glazed, and the carbon is cooked off the piston, indicating some steam-cleaning going on that shouldn't be.FrankZ, being the gentleman and scholar that he is, brought over a fairly fresh head that he had lying around, if nothing else for comparative purposes, although that turns out not to be the case. Interesting that my head, an 0630 casting, is significantly different from Frank's, also a 0630 casting, although an earlier one. The water jacket outlets behind cylinder #6 on my head are roughly 1/4 inch from the combustion chamber, and are overlapping a little with the contact area for the head gasket:
Franks are a full 1/8 inch further away from the combustion chamber:
It appears that some coolant, for whatever reason, was sneaking by this weakpoint, and soaking #6 -- it may or may not have been firing, and certainly wasn't providing much in the way of oommph.
There also was a visible crack in the head at the center water jacket outlet, although it did not appear that any coolant had been making it into the #3 or 4 chambers just yet:
The original valve job on this head was not particularly stellar, although given that it put out 90K, I guess I can't bitch too much. Notice how the valve in combustion chamber #3 is so fully seated that there is no margin within the combustion chamber at all, compared to chamber #4 below it:
SOOOOO, I have re-honed the cylinders, put the heavy valves onto my newly acquired head from Frank (muchas gracias, brother, send me a bill), and will start reassembly this week. Oh, and I found a long-suspected exhaust leak in the notorious header junction, so I'll be throwing an APN header on there while I'm at it. Lessons learned: (1)quality control in chrysler head castings leaves a bit to be desired; (2) the 4.0 (and variants) will run for a long time with a piss-poor head; (3) a 4.6 stroker will run tolerably well on 4-5 cylinders; and (4) Frank is da man.
eace:
. There's really no reason that a stroker shouldn't have the same longevity as a 4.0, just doesn't seem to have been the case for most folks, or maybe you just seem to hear about the bad ones on the interweb.
