Backfiring and Running Hot

[rmacejewski]

1977 911
just had engine work done (new studs) where they had to pull the engine and when i got the car back it is backfiring and runs around 225 to 230 degrees under normal driving conditions. They are telling me the reason for the backfiring is that the carbs are dirty and need to be rebuilt. the solution for running hot is to change the type of oil. this does not make sense to me

any ideas?

thanks
Ronnie

[Flieger]

Sounds like retarded ignition timing.

[kach22i]

I had to re-index my distributor to get the ignition timing right. I lowered my temps 30 degrees by the time I was done.

Check for simple thing like:
Did they put enough oil back in, and of the right type, and without cleaning fluid in it?

Also I think you can lower operating temps by adjusting the valves, at least you can make it run more quiet.

Any funny sounds or smells?


EDIT:
Do a forum search (button in blue band at top) using the name of the shop or mechanic which worked on your car. You may find out bad things or good things which may help you weigh the information they are telling you.

[Paulporsche]

Could be a lot of things, incl retarded timing, advanced timing, too lean mixture, clogged fuel filter, incorrect plugs, poorly fitting or bad plug wires, distributor, rotor or cap issues, incorrect oil or low oil level, driving @ sustained rpms, stop and go driving in hot , humid weather, clogged oil cooler or lines...

[kach22i]

Originally Posted by Paulporsche

Could be a lot of things, incl retarded timing, advanced timing, too lean mixture, clogged fuel filter, incorrect plugs, poorly fitting or bad plug wires, distributor, rotor or cap issues, incorrect oil or low oil level, driving @ sustained rpms, stop and go driving in hot , humid weather, clogged oil cooler or lines...

You are correct, but which one of these things could get messed up the worst by installing new head studs?

Don't tell me "all of the above" or all things are on the table. Where would you look first?

I'm more concerned about the shop's reputation. What we have is a first time poster, which possibly means new Porsche owner, which if he is any thing like me seven years ago means he has been fleeced by a bad shop.

[rmacejewski]

yes - stong smell of gas

[Paulporsche]

Good point, George.

Certainly if he's being fleeced, they could have done any or all of the above things deliberately.

If they are incompetent, something like a plug wire pulled out and not put back correctly, or low oil level.

And, since we should get more info from Ronnie about his location and maintenance history, maybe they are merely coincidental, like old plug wires or worn out points.

[rmacejewski]

I am located in Winter Park, Florida. I bouhgt the car from a freind of a friend. The seller knows the shop well and has used them for a long time. My observation is that they are very disorganized but i feel they are honest due to the relationship with the seller. In addition to changing the head studs they also had some work done at a machine shop. Do not see where they replaced points / plugs / wires / distributor

[rmacejewski]

take that back - they did replace the spark plugs

[kach22i]

If air is getting in the engine through a bad head gasket or even a lose spark plug, the air (during combustion) can super heat and blow a hole in a piston or cylinder wall.

It can be anything.

It really sounds like the shop screwed up if this condition did not exist before they "fixed it"..

It's a matter of faith if you trust them to take responsibility or if you feel willing to pay them to fix it a second time.

I would pay another shop to look at it if the owner of the first shop did not say "bring it in so I can see if one of my guys screwed up".

[kach22i]

Originally Posted by rmacejewski

take that back - they did replace the spark plugs

I don't think any spark plug will make a 30 + degree operating temp difference.

Timing and bad headstuds or head gaskets will make a 30 degree difference.

I think that the magnesium case of the early cars (1977 and older) wears to a non-perfectly round shape verses how the 1978 SC's and beyond aluminum block "breaks in".

Did they rehone cylinder walls or put new rings in?

Can you post your invoice?

Is it possible that there is extra friction due to cylinder alignment or moving from headstud installation?

I'm no expert, just asking.

WTF?..........it just hit me, they had to change the oil to replace headstuds!

What oil they charge you for?

I'm getting a bad vibe about this shop.

[rmacejewski]

i do not think they rehoned the walls or put new rings in and the invoice does not say what kind of oil
no able to post the invoice but here is the info:

oil filter - $13
Head Gasket Set - $235
Case of head studs (24ea) - $948
Bolt Extractor - $55
2 ea throttle cleaner - $20
head nuts and washers - $72
oil return tube seals - $25
spark plugs - $32
machine shop - $350
oil - $48

[Paulporsche]

Ronnie,

As you can see there are a lot of possibilities here. For FL you should probably use 20W50 oil. Do you know how to check the oil level on a 911?

You may have to check your manual or do a search for which plugs. They may be Bosch heat range 7, but I'm not sure about that.

Your dwell angle (points) should be 38 degrees +/- 3.

Your manual will tell you about ignition timing spec.

Did I read you bought the car from a friend of a friend? Can you contact him for info re previous conditions.

Has anyone done a compression and/or leakdown test to check the condition of the engine?

Do you have an oil cooler in the front right fender? Does it get hot when the engine does? Be careful, it can get very hot!

Have you had your mixture checked w/ an A/F or CO meter? Too lean can cause high temps.

[rmacejewski]

Yes - i checked the oil level and it was fine (checked it after running the car for 30 min)
The seller did have the engine rebuilt once after over reving it
don't think a compression test has been done
not sure if i have an oil cooler - what does it look like
i am taking it to a very well respected local porsche mech next fri for them to check it out

thanks so much for the input

[Aurel]

Buy a timing light, check your timing. Invest in tools rather than in a shop. You will learn and derive a much greater satisfaction from your Porsche ownership. This is a 31 year old car, things will break, and only you can really be on top of it. Be your own mechanic.

Aurel

[Por_sha911]

Originally Posted by Flieger

Sounds like retarded ignition timing.

Sounds more like a retarded mechanic!
If the car didn't have these symptoms before the repair, then he needs to take it back and say "you screwed it up, you fix it". Is it possible that the cams weren't timed properly?

[RoninLB]

wild guess is that they turned the crank backward to fit something, caused slack in the cam chain, and it jumped cam timing..

or like the the distributor was installed 180 out or off proper gearing..


I'll take the prize behind curtain #4.


also with carbs it's somewhat easy to tell what direction the engine miss is coming from if you have a lot of shop experience with them. It's either distinctly ignition, fuel, etc.. kinda like take the air cleaners off the carbs and slam the crossbar till it's spitting and coughing through carbs or exhaust till you think it's ready to blow up.. look for fire, how it coughs, how it breaks up. If it's a customer's car it's easier to put the engine through the beating.


good entertainment for me... thx

also some say Ronnie, Ron, Ronald comes from the Egyptian god 'Ra. The sort of pronunciation leads to majesty.

[rmacejewski]

how difficult is it to set the timing?
i do not have the owners manual

[3.2 CAB]

Maybe I an just not current on the price of head studs, but is this really about what they should cost?----------------------------Case of head studs (24ea) - $948
Did they give you this tool they bought for you, or are you required to furnish this shop, tools that they don't have??------------------Bolt Extractor - $55

[Bobboloo]

993 Dilivar studs cost about that much. Hopefully that's what they put in. That'd be my choice for a mag case motor.

Did the motor have these issues before you had it repaired? If not then, bottom line, it is on them to solve it and not charge you for it. Period.