v-tach

my car which is a 1986.5 -- has been on the sluggish side latley...so i did a compression and cyl #5 had a low compression around 50psi...others were 150 and better !
now - what needs to be done - i did not do a leakdown yet ...but can a valve be fixed in the car or the motor has to come out ???
thanks for you help !
v-tach
1986.5 928

AO

Motor need to come out... sorry.

Imo000

No it doesn't and I've posted this in the past that the motor can stay in. The driver side will be a very tight squuez but it will come out.


Do a search on my name and you'll find the post describing what it takes to do this.

As a matter of fact, I'm in the middle of pulling the driver side head off again and just like, before the engine will stay in the car.

Mike Frye

I'm assuming you're both referring to pulling the heads?

BC

Could be some carbon on the valves?

Imo000

yup, that could be too. If the engine is not backfiring then the problem might be the exhaust valve. You cond run some conbustion chanber cleaner or plain water throught the intake. Just make sure you know how to do this properly or else it can hydrolock.

checkmate1996

I would also do a leakdown test to help further troubleshoot the problem.

If the heads need to come off, you still may need to take the engine out. It all depends on how tight those bolts are and if any break. If they do, you are definately pulling it...

I'm feel for you...I hope it's something simple!!

atb

I don't believe a bent valve allows the cylinder to hold any compression, so you're probably okay in that department. If its bent at all, it won't seal against the valve seat, and you will read 0 psi, not a reduced number.

Kevin in Atlanta

I vote for an Italian tune up.

Courtshark

water cannot be compressed... engine goes boom unless the water injected is a VERY fine mist.

Another option is to get a BG power flush cleaning done. This must be done by a trained professonal, tho.

atb

Oops sorry, thought someone had diagnosed a bent valve. Disregard prior post.

AO

I worked with BigDave on his motor a bit and I did not see any way to get that sucker off in situ. Imo000, I think you were either very lucky or the properties of matter are different in Canada... oh, that's right you guys are on the metric system up there. That explains it!

An Italian tune up sounds like it might be worth a shot.

BC

Seafoam treatment twice or thrice, then Italian tune up, an oil change, and then see.

If that doesn't work, then its off with its heads.

Imo000

Courtshark,

And neither can gasoline for that matter. As I sad above, you need to know what you are doing. Steam cleaning the combustion chamber with water is an old mechanic's trick. It works well but you have to be very careful how fast and how much water is being ingested. There is quiet a bit of a margin for error. I've done this myself on several cars in the past and it works like a charm!

You can try using a spray bottle but it will take some fast pumping to get enough water in there to do the job. Usually the way to do it is to disconnect a small vacuum line and let it sit in the water. It will draw enough water through to clean the engine but not enough to hydro lock it.

I know Chrysler actually sells a combustion chamber cleaner that has the instructions printed on the can. The chemical in that can is 99% water too.



Andrew,

I know what you mean when you say that you didn’t see how it would come off, but it does. I’ve done it and will do it again in a couple weeks. I will take pictures to show, that it is possible. My car came from Boston so it is actually a US market 928.

Now there is only one variable that can make this not happen. If the motor mounts make the engine sit higher than mine, it will probably make removing the heads impossible. My MMs are still OK (the engine rocks when revved) but they might be partially collapsed too. Either way I had to use some wooden wedges and a thin piece of plywood to squeeze the head of the studs and away from the break booster. Once it was off I ground off about 1.5mm from the top of the rear bottom stud. This was enough to let the head slide in without any wedging and didn’t effect the head nut either. Because of this, this time around the head should slide off with minimal effort.

AO

Cool! Looking forward to seeing the writeup. :thumup: