GT4 Engine Dead

Hi All,

I suspected that I was low on compression on CYL8 of my GT4 so I performed a compression test.

CYL8 - 165
CYL7 - 180
CYL6 - 185
CYL5 - 175
CYL1 - 170
CYL2 - 0

I then went to test CYL4 to make sure my compression guage was working properly when the engine would no longer turn over.

Just before the engine stopped turning over CYL4 measured 170 so my guage was ok and CYL2 was indeed 0.

Now I can turn the engine by hand in the wrong direction slightly (so it's not seized) but can only turn it so far before it stops solid.

Any ideas as to what may have happened?

I didn't even make it to CYL 3.

Looks like it may be time for a rebuild.



George

 

i would think it jumped time, and bent a valve.

 

Definately sounds like it jumped the belt, If you have or know anyone with a borescope try scoping the cylinders, but the end result sounds like trouble..sorry to be the bearer of bad news.

 

Well after having a break to contemplate the $$$$$ ahead I had another try at turning the car over by hand.

It will turn 1/4 a revoultion and then stop at both points.

It were only 1 valve bent then surely it would turn more than 90 degrees. So I assume more than one valve is bent.

Either way before it stopped turning over #2 cyl had no compression.

I put my hand over #2 and there was no air flow then I tried # 1 and got plenty of air flow. Which confirms what I measured with the compression guage. Not long after trying this it stopped turning over.

Just wondering why it would slip a belt when just turning it over with the stater and all plugs out?
The engine was warm but not fully warmed up.

 

i think the heads are going to have to come off at this point, and you will know more then as to the why and how.

how old were the timing belts?

so sorry to read of your troubles.

 

Timing belts were just under 3 years old.

I just can't understand how this could happen whilst performing a compression test with all plugs out.

If cam belts can jump at stater motor speed then what hope do they have at 7500 rpm.

The car was running great, good power. The only fault was at idle CYL 8 would not drop idle RPM when spark was removed.

Spark was good so I thought a compression test was in order.

Yes CYL 8 was a little low @ 165 PSI but I didn't expect CYL 2 to be 0 PSI and for the engine to lock up.

Still CYL#2 was 0 so it's off with the 1-4 head for a look inside.

 

If you can rotate the engine back to the timing marks, you could find out if it had slipped a tooth. Also if you could get #2 to the top of its firing stroke, you could use a compressor to blow air into the cylinder. It the air escapes through the exhaust, or the intake, its a valve; and if it is blowing past the rings and into the crankcase, the compressed air will escape through the dip stick hole.

 

Any chance that something fell into an open spark plug hole? A socket or something small could be stopping the rotation.
Check around the belts also for an obstruction.
Dave

 

If it was turning over fine before you preformed the test perhaps this is a good sign and there is minimal damage. Is there some sort of retainer that holds the valve in place? If it fell apart only during the test and not while the engine was running this could be very lucky? Good luck and move with caution, dont force anything.

Cheers!

 

Hi All,

All was going well with the compression test until I tested #2 with 0 PSI.

Then when checking my guage on #4 there were some strange noises. #4 checked out ok but when I went back to test #2 thats when the starter could not turn the engine any more.

I guess anything is possible and something may have fallen into an open plug hole but I'm not missing anything.

The other issues could be that something is stoping the engine from rotating on the starter and ring gear.

The car was running fine and I never suspected #2 would be 0 psi.

I would recon that the engine was fine except for #8 @ 165PSI and I stuffed it doing a compression test.

I can't rotate the crank far enough to get back to the timing marks to check to see if the belts had slipped. It will only turn less than 90 degrees.

I guess the old saying "if its works don't try to fix it" applies here.

I think it'll be going on the market when fixed as I'd hate for this to happen again.

George

 

Sad to here this George.If you still have the original sodium valves it might broken off at the stem and is stuck in the cylinder

 

SO sorry to hear this George... unfortunately I think Maurice might be correct as start up often seems to be when the sodium valves break and would explain the 'fine one minute, broke the next' time frame.

 

That's what I'm thinking, is the most likely obstruction, too.
You'd think they'd be replaced by now in a '75 but there's plenty of cars that've never had the heads off.
Still, if it is that its probably the least damaging way you could have it break. Better than dropping at 7K rpm.

Do you have access to a 'scope?

 

Thanks Karen and Maurice,

I'm hoping it's just the 1-4 head. Interesting about the sodium valves. I heard what sounded like a misfire just before things went pear shaped. Fuel was drained from the carbs and spark was disabled so I wounder if the noise I heard was sodium escaping from the damaged valve. I can't turn the motor over very much at all so I'm guessing the valve head or what's left of the stem in now in the pot jaming the pistons progress.

Anyhow I'm in for some late nights, I think I'll start tonight.

Karen, who's the best person to take the head to for repair?

Cheers

George

 

I reckon at least 85% of GT4's have the original sodium valves.When I was looking none of the cars including the one I ended up buying had them replaced

 

George if its only a broken valve and no other damage has been done then just replace all valves or at least the exhaust with stainless,fit new guides and seals and the car will be right for along time.

 

Ok,

Here's the damage. Spot on Maurice

Looks like #2 Valve head broke off and the stem then punched through the piston crown just by cranking it over with the starter to do a compression test.
Is it possible to change the piston with the engine in the car?
Also how can you tell if you have sodium exaust valves fitted?

Could I just fit a new piston (assuming there's no damage to the conrod etc) and get the head repaired and fitted with SS exaust valves?

Also what $$$ would I be up for to have the piston replaced and both heads rebuilt with SS valves?

I have also included some pics of the 1st cam bearing caps. Looks like they have been repaired. The endplay surface is not parrallel either. Is this OK?

All suggestions most welcome.

George
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Sheet George that dosen't look too healthy.Your in a bit of a dilemma here.What are your intentions with the car?Sell or Keep?A valve job will cost around 5-7k mark if your not doing any of the work yourself, maybe 2-3k if you are.Engine rebuild 15-17k depending on what else you find.I dont know about replacing just one piston and no unfortunately they cant be replace in situ.The engine has to come out and be seperated from the gearbox.You will obviously have to check whats going on with cyl 8 as well,maybe just valve guides leaking that was giving you the low compression readings.A question though,How did you pull off that head in such a short period of time?Did you use a puller?Was it easy to come off?It may have been recently removed by the look of things.And yeah the bearing cap doesn't look all that healthy either.

 

Hi Maurice,

The head came off pretty easy with a slide hammer. I don't know if I'll keep the car.
I guess if the engine has to come out then I'll get it rebuilt but @ $15K it may not be happening this year.

I'm in shock, I just didn't think it would happen to me.

I might consider putting in a replacment 2nd hand motor until I can get the funds together for a rebuild of the original.

Anyhow I'll sleep on it and revisit in the morning.

Cheers

George

 

Bloody heart-breaking.
I'm very sorry to see those images.
Never really feel safe with any older motor untill I've rebuilt it myself and know what's in there but its nasty to have it forced upon you at a bad time.
So much for me thinking any damage would be minimal.

@Maurice
Guess I shouldn't be surprised the figure is as high as 85% or so. Haven't been interested in these cars long enough to really take on board all the implications of their unique low mileage, high parts and labour costs world.
Enthusiasts of the marques I've experience of seem to have their engines apart for the joy of it any chance that offers. A part of me keeps assuming it'd happen less with F-cars rather than be avoided as much as it seems to be.

 

Hello Brook308.

You can sell it as is, which will fetch the least money and is the less labor intensive method.
You can part it out and sell the pieces, which is a possibility since you seem not to be attached to this car at all. The engine core is worth $5K ... alone? This takes a lot of time and effort and garage space. But, this is likely the most profitable.

Or, you can fix it then drive or sell it. To replace just the one piston, all the exhaust valves, and make it run again is $3K in parts and some machining. You will have to be careful and not touch anything that do not need to be touched (while I am in there, I might as well rebuild the carbs for $300, the water pump for $100, the clutch for $500, the suspension for $500...). To do a full rebuild would be north of $10K. GT4 is becoming a cult car so if it runs at all and has good cosmetics, you can fetch $20K (in 6 months when the economy bounces a little).

You can go slow, one day at a time, and get it rebuilt in 6 months, just in time for the economy to rebound. Then when it runs again, the GT4 may be so spell-binding that you will forget about all its trouble and keep it. Sort of like a super model for Victoria's Secrets. She is high maintenance but worth it for that one night a week.

Best wishes.

 

Sorry to hear about the trouble, but the sodiums dont bend unfortunately.

Im not sure what the engine would cost to ship to the US. but I'm sure we could save you about 4-5K Aus. on the engine/head rebuild here in the states.

Was the liner damaged as well or did it just cleanly flip over and pop through the piston?

 

WOW, very sorry to hear this. Hopefully your damage is limited and this won't be too painful to fix.

What year is your GT4??

JIM

 

What a bummer, if you do the rebuilt you may as well keep her and get your moneys worth out of driving! Heck, you'll have a fresh engine, why give it to someone else?

 

OMG! ...and I thought I had it bad. This is a horror story!

The worst part is that it's not that big of a fix per se. It's just the cost, and the fact that you have to remove the engine and separate it form the gearbox just to get to it.

But look on the bright side. You already have one head off. If you take the other off too...

Then at least you won't end up with THIS DILEMMA!
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