CursedH1
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Its interesting because literally every single H1 shop/tech I talk to (ModMafia, Rubberduck, Tor and others including the shop that is currently rebuilding the engine) have indicated to me that the gears are not something that they recommend doing as its not necessary. Searching back through the HummerNetworkForum.com (which I run) for "timing" results in little to no results. The maintenance manual from AM General doesn't even mention timing when it comes to scheduled maintenance. I just got off the phone with my guy who had actually just called Tor, who implored him to not install the ARP headstuds because 1) They all leak and 2) He's never seen a problem with the factory headbolts. Now I don't know what to do. For those of you who aren't aware, Tor is one of three remaining AM General factory certified techs in the country still working on these trucks. His reputation amongst our community is absolutely unimpeachable. So I'm getting stuck between two camps of people here. The group that seems to be H1-centric that says "don't do it, not worth it, it'll fail" - the guy doing the rebuild is one of these guys. "I've been building 6.2's and 6.5's for 17 years now and never had a problem with the factory head bolts." Then there are people like Will and Chris who are telling me to do everything from gapless rings, head studs and flash cleaning. In the end I'm probably making all of the wrong decisions all over again and I'll just be back here again in 6 months wondering why I even f*cking bother.
Thank you for nominating me for the Carnage of the Year award - however I should probably occupy a place in that award's Hall of Fame.
In 2019, I blew up my first 6.5 - the #8 cylinder - while driving over the Casco Bay Bridge in Portland Maine. Truck drove about 3 miles puffing white smoke until I finally had it towed away. Had it replaced with a UORVA test mule P400 by ModMafia down in Texas. Never had a problem with that engine.
Until 2021, when a 15 year old girl t-boned me when she pulled out from a stop sign. She hit me right under my drivers' door and I ramped up her hood and did a complete 360' barrel roll. Got it all on dashcam.
Got my current Red 2003 H1 two months later. Managed to get one of the last factory P400's they made in early 2022 - from what I understand it was essentially a "spare parts special" when GEP was cleaning up the factory floor - they found enough components to make 4 more brand new P400's. So I ripped out my perfectly good heavy block 6.5 in my 03 and put the current P400 in with the UORVA turbo and some other things - timekeepers included. Almost universally the Hummer community criticizes me for changing so much on the engine - but my H1 weights 9100lbs, I tow my M1102 (about 2k lbs), daily drive it and also use it for long cross country road trips. It needs to handle the heat generation of going 70mph. Not sure if @Will L. has availed you of the aerodynamic issues that the body of the H1 presents for our cooling stack but needless to say, we overheat when we go fast, whereas we'll actually get too cold when we sit still in traffic.
In August of 2025 I was in the North Maine Woods, about 40 miles from the closest paved road when we pulled off for lunch and immediately everyone in the group smelled coolant. Turns out my fan had intersected with the fan shroud, broke off half of the blades and chucked at least one straight up into the radiator producing quite a leak. We used JB Weld putty as best we could, I filled up a 5 gallon jerry can full of lake water and started driving back towards civilization. Using my two temp gauges and stopping every 5 miles (with the trailer behind me) I managed to get the truck back to our basecamp without breaking 200'F on the temp. I was rather proud of that.
So I had it towed down to my aforementioned mechanic and we had the radiator rebuilt with dimpled cores. Since the fan had lost about 5 of the 9 blades, we decided that it was prudent to replace the waterpump as well. For those wondering if the cover is removed during the waterpump install, per the H1 Shop manual, it is. And this is where the timing gear problem happened I believe.
Timing adjustment is not listed on any of the scheduled maintenance groups throughout the factory manual:
