Low Compression #5 Cylinder--Advice Needed

SNLC

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Tear it down, a blown HG can give confusing results during a leak down test. I bet you have a blown HG.

If ARPs were not used they should be used. I do the torque in four to six sequences depending on my max desired torque. Use only an OEM HG.

A general FYI, exhaust valves are often burned on Toyota inline sixes. We don’t do valve grinds in my shop for this reason, we replace the valves. New valves (and old) can be tipped to get the adjustment correct using old shims vs the big process of shimming the valves with new shims. Its much faster for a machine shop to do as well.

Cheers
 

flintknapper

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Tear it down, a blown HG can give confusing results during a leak down test. I bet you have a blown HG.

If ARPs were not used they should be used. I do the torque in four to six sequences depending on my max desired torque. Use only an OEM HG.

A general FYI, exhaust valves are often burned on Toyota inline sixes. We don’t do valve grinds in my shop for this reason, we replace the valves. New valves (and old) can be tipped to get the adjustment correct using old shims vs the big process of shimming the valves with new shims. Its much faster for a machine shop to do as well.

Cheers

^^^^

This is where I'd go with it....given the info we have.
 
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I'm not trying to argue, more just understand all the recommendations. I've got 3k miles on the rebuild, which included a new OEM HG. New OEM studs were also given to the shop. Did they follow FSM procedures and actually use the parts I gave them? I'll never know, but given my problem I assume no.

I haven't experienced any overheating since then and the vehicle drove fine the first 2700 miles. It did sit, mostly unused, for 6 months while I was deployed. I came home and it drove fine for a month. Hell it still drives fine at any RPM over idle.

How would a HG just blow without overheating or improper install? I'm assuming the latter.

The more I learn about this engine, I don't think there is anything too complicated that a local shop couldn't handle. It's more so the attention to detail and following FSM specs that I want. The closest cruiser specialty shop is ACC, but that's a $1k shipping fee round trip. Anyone know of a trustworthy shop in the Destin-Pensacola area?

If I pull the head, does that automatically require machining? I would think a machine shop inspection is the minimum, but then I'm back in the same dilemma of trusting a shop to do accurate work.


Thanks for all the info and advice!
 

SNLC

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I am fixing a 1HDT right now. Rebuilt right before the owner bought it 20,000 miles ago.

Cruiser came in running real rough and smoking, its a diesel.

Compression test showed low on #2 & #3. Leak down test showed intake valve on #2 and exhaust on #3. So off came the head, once head was removed the HG was blown badly between #2 & #3 just like the pic posted above. I have no idea who did the work, it does not appear new head bolts were used. Multiple head bolts around #2 & #3 were super corroded, removal of these bolts seemed like they we cross threaded in but it turns out they were just super rusty. Cleaning out these head bolts holes there was an absolutely huge amount of rust down in them. This is only after taping them, when blown with air huge clouds of rust dust came out of these holes.

B97928AF-09EA-41D2-942E-709D4A12D777.jpeg


No coolant leaking or contamination from the blown HG, again it was blown between the cylinders. The 1HDT is only running 18psi which is not a huge increase over stock.

You need to tear it down, that’s where you are at with it. You also really should use APR head studs and toque to say 100-125ftlbs, I suggest 15-20ftlb increments. Maybe you don’t need to rebuild the head or bottom end. You best check both though for true with a quality straight edge or you might end up doing it all over again.

Cheers
 

Njck22

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I am fixing a 1HDT right now. Rebuilt right before the owner bought it 20,000 miles ago.

Cruiser came in running real rough and smoking, its a diesel.

Compression test showed low on #2 & #3. Leak down test showed intake valve on #2 and exhaust on #3. So off came the head, once head was removed the HG was blown badly between #2 & #3 just like the pic posted above. I have no idea who did the work, it does not appear new head bolts were used. Multiple head bolts around #2 & #3 were super corroded, removal of these bolts seemed like they we cross threaded in but it turns out they were just super rusty. Cleaning out these head bolts holes there was an absolutely huge amount of rust down in them. This is only after taping them, when blown with air huge clouds of rust dust came out of these holes.

View attachment 2807602

No coolant leaking or contamination from the blown HG, again it was blown between the cylinders. The 1HDT is only running 18psi which is not a huge increase over stock.

You need to tear it down, that’s where you are at with it. You also really should use APR head studs and toque to say 100-125ftlbs, I suggest 15-20ftlb increments. Maybe you don’t need to rebuild the head or bottom end. You best check both though for true with a quality straight edge or you might end up doing it all over again.

Cheers
If you're not pulling the pistons a trick to keep the bores clean of crap when attempting to clean block surfaces is to buy a bucket of cheap wheel bearing grease or vaseline and build a dam between the top of the piston and the cylinder bores.
 
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Check your valve clearances before tearing head off.

To tight equals not fully closing which equals low compression. It will also cause a suction effect from other cylinders and draw more oil into that cylinder giving the impression of a oil wet cylinder.

If clearances are to tight, especially a turbo engine as EGTs run higher, the valve will burn more quickly and also cause more problems.

Check valve clearances before head removal.
 

SNLC

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I thought ARP stud torque specifies 80ft lbs?

I don’t recall off the top of my head on a 1FZ, I use the Opel studs. I usually go to 100ftlbs on unboosted 1FZ’s. Factory torque is 90-100ftlbs, I have checked while doing the two 90* sets.

For the 1HDT they are 75% at 92ftlbs. So 122/3ftlbs is 100%. I went to 100ftlbs on this engine.

Cheers
 
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Ok, I decided to drive until something worse shows up. It’s my DD so I sent it.

Just took it on a 500 mile trip and got a few new codes. Drove fine at speeds up to 80MPH.

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