6G75 heads on 6G74

[aussieguy]

Ok the 350K 6G74 is valve stem smoke is starting to resemble spyhunter when idle on a slope, I did check compression 1 year ago and 2 cylinders where as low as 130ish, so deciding on a refresh.


Q. 380 (6G75) heads are similar / same as Pajero 6G75 non MIVEC?


Q. Apart from different stroke (crank), when choosing the 380 option, if I stick with 6G74 crank and pistons is there any issues?



Q. Pajero crank is stronger, changing the internals to the 380 will weaken?




Thanks in advance, starting on the research.

[erad]

I don't know for sure, but I expect that the 6G75 heads will be compatible with a 6G74 block. However, you should not the following:

1 You had some lowish compressions. Were they on adjacent cylinders? If so, the low readings are probably due to a head gasket leaking between the two. If not, it is worn ring or valves. If it is the rings, changing heads won't help. If the valves were leaking, replacing the heads will help, as long as the valves are addressed at the same time (logical to do this).

2 If you put 6G75 heads onto a 6G74 block and pistons, the compression ratio will be decreased. The definition of compression ratio is the ratio of the cylinder volume at top Dead Center divided by the volume at Bottom Dead Centre. This indirectly determines the cylinder pressures, and increasing the volume at TDC will lower the maximum cylinder pressures slightly. You are probably better to refurbish the 6G74 heads - shave them slightly (maximum allowable grinding limit 0.2 mm).

The 6G75 heads would probably require you to use 6G75 intake and exhaust manifolds as well.

3 The crankshaft should be man enough to take any modifications you can do to the engine.

[aussieguy]

Thanks, after reading the 380 conversion thread I think I will just pull the motor and send it away for a complete rebuild, sounds the best option and cheaper than buying a secondhand Pajero engine.

[aussieguy]

UPDATE - After reading more on doing a 380 engine swap and the ridiculously cheap cost of buying one VS reconditioning a Pajero 6G74 ($3k approx), I'm starting to lean towards an engine swap.


Would like to hear from anyone who has done this, and how they are traveling since the thread on the topic are 3-4 years old, how is the longevity of the swap?

[disco stu]

Just make sure you check with QLD RTA equivalent on whether you will need engineers certificate with the 3.8 first

If its any help I had a thread detailing my dealings with NSW, back and forth about definition of engine family, ADR's etc. That might give you some ammo if you need to argue with them a bit more about it all. Valve set up is the same as per ADR36 (I think it was 36)

[erad]

For what it is worth, my recollection is that the RTA in NSW allowed a 10% increase in engine capacity and this would be OK to go for a 3.5 to 3.8 conversion. I don't know about other states. But the engines are still Mitsubishi with a 6G prefix, so I expect that they would allow the conversion - they wouldn't know the difference - Ha! Even if you cannot find a good 3.8 engine, there are plenty of Magna 3.5 engines around and they present no regulatory problems. The MAgna has a distributor, the Pajero has coil banks so you need a cam angle sensor and bracket, and to change the sump, but I think that that is about all the major items required. There are plenty of posts about this change on this forum.

[Tonestar]

Would an engine swap seriously be cheaper than buying all the required parts/gaskets/seals and sensors including getting acid baths, machining and reassembly (if not self) on your current engine?

With engines in other vehicles in the past, it was always more economical to do that than engine swap or purchase a recon?

[aussieguy]

Would an engine swap seriously be cheaper than buying all the required parts/gaskets/seals and sensors including getting acid baths, machining and reassembly (if not self) on your current engine?

With engines in other vehicles in the past, it was always more economical to do that than engine swap or purchase a recon?

Recon 6G74 $3K thats with me taking it out and putting it back in.


380 Engine $650-$900 + timing belt and water pump + other may as well replace on unknown engine.


So about 1/2 the cost of a recondition.


My 6G74 is 340K and starting to blow smoke when idling for too long, probably valve stems, and when I changed plugs was 20PSI difference between worst and best posts when i did compression. Not in a hurry as probably go for another 50K burning 500ml ish per tank around town, less on long runs.


my interest was sparked because i have been offered a "good" 380 motor for $400.

[Tonestar]

Recon 6G74 $3K thats with me taking it out and putting it back in.


380 Engine $650-$900 + timing belt and water pump + other may as well replace on unknown engine.


So about 1/2 the cost of a recondition.

I would be concerned about the real condition of that engine being unknown as I have been caught out a few times in the past :/

[disco stu]

For what it is worth, my recollection is that the RTA in NSW allowed a 10% increase in engine capacity and this would be OK to go for a 3.5 to 3.8 conversion. I don't know about other states. But the engines are still Mitsubishi with a 6G prefix, so I expect that they would allow the conversion - they wouldn't know the difference - Ha! Even if you cannot find a good 3.8 engine, there are plenty of Magna 3.5 engines around and they present no regulatory problems. The MAgna has a distributor, the Pajero has coil banks so you need a cam angle sensor and bracket, and to change the sump, but I think that that is about all the major items required. There are plenty of posts about this change on this forum.

While that is all correct, what they call family is actually model, if you speak to the same guy I did. To everyone else in the world 6g7 means the family, and 6g74 is the model, but to them family is whatever range of engines was offered in the model. So you can bore and stroke it out to 3.8l, but can't put an original 3.8l in it. I was going to get very pushy given that engine family definition in the adr's they refer to meant crank to cam centre dimensions and valve set up, but I just went with the Magna swap

[shocker1]

A $3k rebuild is cheap. Just a timing belt replacement recently cost me $1K just for parts, labour & other parts not included soon ran the bill to more than double this figure. I looked at an engine rebuild 6 months ago & was quoted $6.5K from a shop in Ipswich. It was rebuild existing engine only, remove/replace the engine & return freight from NSW to Qld were my problem. In the finish I kept the existing engine as the oil burning was not bad enough to be able to tell from the spark plugs which cylinder had a leaking valve seal.

[bundyjr]

if your looking to buy a 6g75 don't bother with wreckers buy a hole car at least that way you get something that's running that can be tested. Hit pickles ect I payed 1200 bucks for a manual vrx 380 and made all my money back parting it out so conversion cost me nothing but my own time.

[aussieguy]

A $3k rebuild is cheap. Just a timing belt replacement recently cost me $1K just for parts, labour & other parts not included soon ran the bill to more than double this figure. I looked at an engine rebuild 6 months ago & was quoted $6.5K from a shop in Ipswich. It was rebuild existing engine only, remove/replace the engine & return freight from NSW to Qld were my problem. In the finish I kept the existing engine as the oil burning was not bad enough to be able to tell from the spark plugs which cylinder had a leaking valve seal.

Downs Engine Rebuilders (Toowoomba)
Quoted $2800 for SOHC Pajero 6G74 rebuild, engine removal and etc had to be done by someone else... me.


Last engine rebuild I did was a RB20 15+ years ago, since then I got old and lazy, but after helping a mate build his Winebago (Renault based) engine the past few weeks I decided I might as well give the 380 conversion a go, the paj isn't a daily and I have a shed full of gear to do the job.