Engine blues again!

[OzCoupe72]

G'day everyone

I have been away for a while enjoying driving my 72 coupe even entered a few car shows with plenty of interest in the only 7173 in attendance

As some of you may remember I had some issues with my stroker engine last year in which it prematurely retired due to thrust failure along with (perhaps?) tight bearing clearances contributing to a sudden loss of oil pressure

Engine machinist couldn't find anything conclusive and just put it down to tight bearing clearances

My memory not being the best I believe I had checked them against the tolerances listed in my performance rebuild book which at about .0010 to .0015 I can vaguely remember the flexi-gauge reading was about .0015 which would be fine for a stock engine but have since learnt a bit tight for a performance engine

Kicked myself up the backside severely for this and decided to pay the experts to assemble the short block this time round - almost $5K for this one

Last Sunday went for a run and started to notice an odd rubbing/rattling sound coming from the engine/trans area

Oil & temp still good so took it easy and got it home to inspect

Sound was coming from the bellhousing area so suspecting a loose/cracked flexplate I removed the inspection plate

After looking for anything obvious I decided to lever on the flexplate and sure enough it moved about 3/16 inch so was hoping just a flexplate but after talking to my trans guy who knows the car well he said he wanted to look at it as it could be the engine thrust again and my first thought was no not again!

Sure enough once on the hoist with one watching the balancer and one levering on the flexplate they both moved in unison - damn damn damn!!!!

Now before anyone chimes in we previously explored the trans/convertor excess pressure on the crank causing thrust failure but didn't find anything conclusive but despite this replaced the converter and had the trans guy go over the transmission regardless

Although the engine has been going well the last few months it has recently been using a tiny bit of oil with a couple of times at high rpm (limited 5900) there has been a little smoke and not just from the tires so my gut feeling was something wasn't right

Naturally I'm devastated that once again I have to tear down the engine but first I need to conclusively eliminate the transmission side of things so will be doing a pressure test today, My trans guy who has worked on and driven this car several times has doubts the trans/converter is doing this because if the line pressure was excessive I should have extremely hard shifts which is certainly not the case

I'm also going to check every other avenue including trans alignment and crank run out as the block was align honed

The only other thing that could be causing premature thrust failure is it is just a bad crankshaft from the start

Crank is a Scat 9000 series cast and these are supposed to be good to 600hp

I have not found many negative reviews of this crank but who knows?

Anyway a long way to go and can't afford to let this happen again so will be a long process to find the cause

I will welcome any suggestions from members but reckon by now I have researched every possibility ten times over

Can't afford to fix it straight away anyway, apparently there's some bug getting around and the missus has had to close her business down so no extra cash for the mustang unfortunately

Reckon the crank is beyond repair this time so will probably go with a forged 4340 this time round. Also the block may be buggered as well but have a spare standard bore block so hopefully the pistons/rods are still good.

 

[c9zx]

Oz, I have contacted a friend in Australia who has great knowledge and experience with these engines. Hopefully you will hear from him. If you do, carefully consider what he tells you. I know it sucks right now. I felt the same way when I had 8 Scat I beam rods go out of round on the Dyno and toast a new Boss 347 build. It took me almost a year to gather up the funds to "go again". Hang in there my friend. Chuck

 

[OzCoupe72]

c9zxOz, I have contacted a friend in Australia who has great knowledge and experience with these engines. Hopefully you will hear from him. If you do, carefully consider what he tells you. I know it sucks right now. I felt the same way when I had 8 Scat I beam rods go out of round on the Dyno and toast a new Boss 347 build. It took me almost a year to gather up the funds to "go again". Hang in there my friend. Chuck

Thanks Chuck and yes it really sucks to have this happen a second time

I will contact Jason shortly, appreciate the help

Yesterday I performed a line pressure test on the C4 with perhaps some interesting results

In forward gears at idle between 110-130 psi with very little change at stall even slightly lower

Neutral and Park between 110-125 at idle dropping a little when engine revved

Reverse was off the gauge but my gauge only reads to 140psi

I'm concerned about the high pressures at idle so will consult with my trans builder