Head gasket replacement on 90 Q45

[rooster1]

Anyone have any PDF's on doing this repair? The car is about 100 miles from where I am, Broke down, and I believe it's the head gaskets. Thing ran hot and now won't start. No water in the oil but it could have blown off when the cap blew. Engine turns over easily though. The only thing I can think is that it is a compression issue and I am hoping new gaskets will solve it. I have changed them on plenty of fords and chevys, but never on an infiniti. Any help would be appreciated as regards to tech info and how-to. Thanks.

[ericthered]

These engines don't have a history of blowing head gaskets pretty much ever.

First question is whether the timing chain guides have been replaced or not. When these fail the timing chain can jump... it is an "interference engine" meaning that when wrongly timed, the vales can make contact with the cylinders, resulting in general very badness. This is a common problem in 1993 and earlier Q45s - you read about it in many many posts.

Usually the engines just stop, and don't overheat first, AFAIK. Did your overheat, or was it just hot? I don't know if there is a possibility that the engine can still turn OK if the valves are already bent out of the way. Others with more experience here will know more.

In any case, if its not chain guides, then I'd start looking at other issues before declaring it is a head gasket.

[rooster1]

chain guides were replaced by previous owner. I have weak compression in 3 cyclinders which is an indication of a bad head gasket/ warped head rather than bad valves. I should say the better bet by most mechanics is that when you have multiple cyclinders with weak compression most of the time you are dealing with bad gaskets and/or warped heads. Could be bad valve though but the engine turns very smoothly with wrench attached and plugs removed. First indication that the car was hot was a stutter and then a blown relief valve on the radiator cap. Dash temp gauge is snafu. I am mainly concerned that there is no sign of water in the oil pan but that doesn't necessarily happen when you blow a head gasket.

[Q45tech]

It is much easier to swap engines than to properly replace both head gaskets with engine in car. You will need brand new head bolts and heads, cams, hla, springs, valave stems seals - in short brand new heads!

Overheats will have cracked and destroyed BOTH KS and you will need to replace all rubber hoses..............every single one.

The oil will have coked and destroyed the bearings and worn the crank and front and rear main seals...............have seen some so hot they conducted heat into and destroyed the transmission.

Aluminimun engines must never exceed 350F.

All aluminum V8 are designed to be replaced when overheated unlike cast iron units which may survive.

Preventative mainteance replacing cooling parts before they fail and attention to prefailure signs and signals are mandatory with expensive exotic engines.

Like all aluminum engines the temeprature sensor goes high then drops to normal when the coolant turns to steam and loses contact with the sensor.

Not paying attenion and missing the the climb and fall [occurs over 5 minutes] gets you a new engine.

[rooster1]

much to consider there. Unfortunately gauge has never worked. Thanks for the insight.

[maxnix]

Flatbed to a garage with a lift, proper jacks, air tools, engine stand, etc. will be your best bet.

[96Qowner]

Here's a great series of threads by BlackBirdVQ, who rebuilt an overheated VH45:

Just bought a Q45

Blown head gasket

Some engine pictures

Cardomain pics

And then he spun a rod bearing ...

Clogged up oil screen

And then, IIRC, he blew it up again.

Be advised, it's better (easier/cheaper) to put a used JDM in it.

[Q45tech]

Not just any used JDM engine but one inspected before purchasing by an expert who is familiar with the look [down the oil filler port] and the general cosmic vibrations such an engine eminates sitting on it's packing crate.

Gotta be careful as many JDM junkyards and importers steam clean them and polish and silicone coat and internal oil flush to make a purse out of a pig's ear.

You need to buy locally from someone who will take the engine back when you open it up to replace guides/valve covers and find other defects.

Buying on ebay is a gamble, but so is not knowing what to look for by the typical engine swapper.

[AlabamaDan]

So educate us on what to look for. I bought a used engine for my Sentra years ago after I threw a rod. Guess I got lucky cause I was young and just took the guys word for it.

[Q45tech]

Pretty difficult to educate the ocassional-one time buyer buyer.I would recommend you pay an experienced automotive engineer to shop for you and examine the possible choices.

We don't know if we have gotten a good one until the valve covers are removed and the guides are replaced...................exposing the insides.Same with pulling the oil pan and looking.

Luckily we buy enough so the wholesaler will take back our rejects.........we are still out time and labor getting to a reject decision but when you give a 12/12 warranty you better be right or you get to do a lot of new work free.

That's the problem people think of these as only $1000 engines when the proper process is $5,000.

You get what you pay for ----- sometimes