Rocker arm keeps breaking for cylinder 5 and sporadic factory temp needle

Hello members.

Motor: TB42e (EFI), duel fuel (LPG and Petrol).

Quick chronological order of events:

- major breakdown approx 5 weeks ago, Hydrolocked in stationary position trying to crank after head gasket blew. I knew better not to as well. Oh well. Head gasket blew, pouring coolant into cylinder 5 and 6. Only physical damaged observed after pulling head off was bent pushrods for intake and exhaust valves for cylinders 5 and 6. I checked valve heights, also turned crank to check each pushrod height and piston height. All seemed well, only some pushrods bent.

- installed new thermostat, water pump, 3 core radiator, gaskets, filters, spark plugs.

- after replacing bent pushrods, I used HOT rocker arm clearance values, but I knew I was too slow by time I got to cylinder 5 (motor was no longer warm to touch), because of zero Celcius ambient temp.

- rocker arms for cylinder 5 EXHAUST and cylinder 6 INTAKE snapped. Took me couple of hours to finally realise what had happened, and that it was likely due to being too slow when setting valve clearance. Because, I had also repaired, rewired and modified most sensors. Was driving me mad, lol, thinking motor was running rough because of my wiring.

- replaced broken rockers arms (cylinder 5 exhaust and cylinder 6 INTAKE). Checked height of valves (after rocker shaft off), pistons and pushrods heights seemed good after turning crank few revolutions (hand crank). No big deal.

- after replacing broken rockers, I used COLD setting for valve clearances.

- then I installed new after market temp guage (cheap Dragon brand which is great value).

- rocker arm for cylinder 5 EXHAUST snaps again. Hmmm, maybe it was because of blocked oil port on rocker arm or rocker shaft is warped bent. Nah, oil ports were not blocked. However, I forgot to check rocker shaft if warped. Damm it.

- accidentally left home made bleeder valve open during testing after replaced rocker arm for cylinder 5 EXHAUST. Damm it, coolant erupts over plenum and intake manifold, ingress into custom fuse box and some Earth points. Oh well, air compressor comes out again, clean and wipe. No dramas. Darn it, now the factory temp guage needle fluctuates (flutters/micro seizure). Hmmm, probably just a bad earth from damm coolant spill. But, then I would notice sometimes the after market temp guage hitting 120 degrees Celcius. Say what! This is not long after warming up from idle too. Weird thing is, upon turning off and cranking over again the temp reading on after market guage goes back to normal 85 to 90 Celcius mark. Seems like there is a cycle pattern going on to. Maybe every 5th time I start the motor again, the temp reading on after market guage hits 100 to 120 Celcius. Realised then only one conductor off after market temp sensor running back to guage, so I would need to earth the guage to get control voltage for temp guage.

- however, today I was about to embark 100km journey, with micro fluttering factory temp guage and part time lying after market temp guage, when just after about 20 meters of slowly driving with full vehicle load, I heard a dreaded snap again. Checked tail pipe with paper towel, and lo and behold, damm rocker related again.

So, I have deduced this ongoing broken rocker arm continued problem to one of following:
1) over torque of rocker shaft and arms (I basically did up much as I physically could with spanners (but only using one arm for leverage). The factory torque settings did not run off on me, paranoid it was too low, hence I normally just hand torque with no torque wrench for rocker assembly. So, maybe it is user error, typical, and I should just stick to literally spot on factory torque values (16 to 20 Nm or something I don't have book beside me right now).
2) warped or bent rocker shaft
3) possible blocked passageway in coolant system, likely from throttle body to plenum (I suspect this after recent blown hose there and also noticing no coolant or air coming out of factory air bleeder on plenum. Hmmm).

Things I've continued to do and check over, since initial Hydrolocked:
- combustion gas test (no CO2 from radiator cap)
- compression test (all over 170 PSI, and all within 8 PSI - pass)
- usual checking electricals all the time, just a habit (pass - except for recent sporadic temp needle and after market guage occasionally show 120 Celcius since coolant spewed out from bleeder valve I forgot was open during idle test)
- checked valve heights (when rocker shaft off) (pass)
- checked camshaft by turning crank and comparing every pushrod height to be equal at peak and trough (pass)
- checked spark plugs, ignition, dizzy and coil (I always do this if misfire or miss observed) (pass)
- leakdown test (20%)
- timing (always always always check timing anytime there is miss or rough idle) (pass)
- alternator (just for barrel of laughs). (pass)
- checked conrods, by comparing every stroke of each cylinderz and obviously look up through sump (pass)

Things I have NOT checked:
- rocker shaft deviation
- whether there really is a blocked coolant passageway around throttle body and plenum. Now thinking about it, the only bolt on component I did not clean or check was throttle body, but this did not seem important since there was evidence of flow after rebuilding top end. It only manifested as concern after hose between throttle body and plenum blew. It was clearly perished and old, so I just figured nothing of it till now. Since after replacing that hose section, I observed sometimes coolant would deep out of two air bleeder valves (one factory and one is custom inline to return heater hose to LPG setup.

Something I also noticed, just before heading out for a drive, there didn't seem to be suction from radiator when I was checking for bubbles. Hmmmm.

So, maybe blocked coolant passageway somewhere. Has to be throttle body or plenum, if so. However, this would be classed as independent of block and head, since throttle body comes off Tee barb from head after heater hoses. This barb is also brand new, I fitted myself easy enough.

Motor is cooling down now. I'm at truck stop semi broken down. Have roadside assistance etc, but prefer to fix and save money, as I'm a student nowadays.

I have all tools on me, except no hoist and crane now.
I have spare rocker assembly and pushrods. I also have two spare heads that need reconditioning. But, I'm doubtful this new cyclinder head needs to be replaced.
I have spare new 10 litres oil.
I have new coolant and spare containers to recycle.

I do not have a handy parts store or auto store nearby. So, whatever truck stop typically sells is what I can buy if needed.

I'm okay at moment. Its a great truck stop. Nice spot where I pulled up, not noisy, and plenty space on grassy area. Toilets, okay food, water and showers here. So, I am more than happy to literally sleep in vehicle here while riding and repairing motor. Would be nice to do before another week though.

Please yell out suggestions. What to check, what it could be, your opinions appreciated.

using the hot value on a cold engine wont do any harm it will just leave you with more clearance than ideal, my thoughts are you have probly got a bent valve stem or 2 given you bent the push rods and are still snapping rockers

Bent valve stem as suggested would be the first thing to look at.