08 Hemi Rebuild Questions/Problems

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yesitsgotahemi

Junior Member
Joined
Jan 17, 2021
Posts
3
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Location
Hemiville
Ram Year
2008
Engine
5.7
Hello all, long time reader/first post. I'm trying to diagnose a very rough idle in my hemi. I just rebuilt the engine and am in the middle of tearing it down again to figure out what is wrong. It's in an 08 Ram 1500 with 205k miles.

Engine specs:
Sealed Power H899CPA Cast/Hyper pistons
New clevite main/rod bearings
stock rods
no work done to crank
heads milled 0.006"
comp cam stage 2 HRT (220/230 .596 lift, 113 LSA)
Can't remember the brand, but springs rated to .600 lift
enginetech non-mds lifters
mds block off plugs
custom length howard cams pushrods
new water pump, oil pump, timing set
fel pro stock thickness head gasket

Basically just a rework.

I'm tuning it myself with HP Tuners. I am not an expert by any stretch of the imagination, however I have seen many tutorials on how to get a hemi to idle right, and none of them are working. The fuel injectors were pulling 38% LTFT at idle. In order to get the fuel trims right, I had to lower the VE to something like 41% which is just not right.

Hear either a exhaust leak or valvetrain clatter at idle. I put on BBK shorty headers, which are extremely difficult to tighten down. However I stuck a hose in my ear and probed the head/header and header/downpipe connections and didn't hear any losses. The old timer screwdriver to the ear trick seemed to indicate a good amount of noise around the valvecover area.

I decided to pull all the plugs (Keep in mind the engine has maybe 2.5 hours and only 22 miles on it) and they all looked fine. I measured the compression at between 120 and 130 for each cylinder. A flag went off. Before the rebuild, it burned oil quite bad and the #7 and #8 cylinders had somewhat oily plugs. Despite this, she had between 150-160 psi on each cylinder.

I don't have a leak down tester yet (It arrives today) however I brought cyl#1 to TDC and put shop air in it. I could hear air going into the crank case (At this point the oil pan was off, front timing cover was off). I know engines have a certain amount of okay leak. Thinking I might have the wrong pushrod length, I loosened up the rocker shaft bolts to the point the valves were full closed by the springs. Re-did the leakdown test and the air "sounded" the same. I checked the timing chain and it is spot on according to the manual. The dots lined up, the valves were both fully closed on cyl#1 and the crank keyway was at 2:00.

I still have the OE parts from the rebuild. I noticed that 1 piston was different. Seriously. 7 stock dodge pistons and 1 2009+ dodge piston. I've verified the pentastar casting on the back, the Mahle "M" on the face. I re-used the rods, but I don't remember any of them being the "newer" 09+ rod. I looked at pictures online of pistons and also compared the ring packs and the single piston is definitely at 2009+ with the smaller 1.2/1.2/? ring pack over the 1.5/1.5/? 08 style. The 7 pistons are stamped "21_015" on the top. I found very few references to this online. One person thought it meant 0.015 over, but I don't know of any 0.015 over sized pistons. And these have the pentastar logon stamped on the back and I don't think Mopar makes oversized pistons. I think the 015 actually refers to the dome height. I think the 21 refers to 1.21" compression height.

When I did the rebuild, I didn't have access to a borescope, so I didn't measure the bores. There wasn't any ridge that needed to be reamed and there was a cross hatch still visible, although it was glazed.

In case you are tracking, I'm beginning to wonder on if the pistons were the right ones. I replaced with standard sized pistons and rings. I noticed the speed-pro catalog said these are up to 2005, however I've seen other brand pistons which are 03-08. So I'm not sure if there is a difference. There is a different OEM part number between 03-06 and 07-08, however the stock part number is a piston/rod assembly and not the piston itself. I took the numbers from the piston specs and plugged them into a CR calculator and got 9.87:1.

This is highly subjective but when I put the pistons back in the cylinders, it was a tight fit and didn't feel loose. I did check the ring gaps before I installed them. The spec for the top ring is 0.23 to 0.38mm and 2nd ring is 0.35 to 0.60mm. All measured between 0.356 and 0.381 (The two closest in size with my feeler gauges) gap. For the 2nd, all were between 0.457 and 0.508

Measuring the oil rings is tricky, but I got between 0.559 to 0.610mm and the spec is 0.15 to 0.66mm.

I'm thinking of artifically reducing the pushrod length by putting a metal spacer between the rocker shaft and the mounts for it. Then bumping the starter and seeing what that does to the compression. As a side note, I measured compression and listened for leakdown on all of the cylinders, so it's not just a problem child.

Questions:

So the gaps are on the high side of normal, but still within spec. If for some how, some reason, these are 0.010 overbored cylinders, would my gaps still be within spec?

Does anyone know for sure if Mopar does make oversized pistons? And confirm the 21_015 numbers?

Does anyone know if there are any differences between the 03-06 and 07-08 pistons?


Thank you for your thoughts and sorry, I know this is a very long post.
 
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yesitsgotahemi

yesitsgotahemi

Junior Member
Joined
Jan 17, 2021
Posts
3
Reaction score
0
Location
Hemiville
Ram Year
2008
Engine
5.7
Update: took off the front timing cover and timing was spot on. I decided to unbolt the intake rocker arm shaft and put a zip tie between the head and the rocker shaft. Basically using the zip tie as a spacer to make the intake pushrod appear shorter. Lame I know, but just did it to test. Low and behold, instantly got 170 psi. I then did the same for the exhaust and didn't see any improvement, so it's clear that the pistons are fine, but I need to get some new pushrods.

I also did some math and, figured out the circumference of the OD of the ring, with both the widest and lowest gap. I then figured out the circumference if the bore was 0.010 over, and looked to see what the gap would be. It would have been over 1.0mm gap, so it's clear that I am still running stock diameter bores.
 
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