911 new rebuild - rough running with a rattle

[clarelaw]

Just finished rebuilding my 81 911 SC 3.0 CIS rebuild. Mostly stock with JE Pistons and cat by pass pipe. She started on the second try but runs very rough and backfires. After the 2000 rpm idle period, when I place the engine under a load, I hear a loud rattle, like the engine is lugging.

I have check my plug wires - correct for the SC per Waynes book. I will recheck the static timing before I start it again. It is the rattle that worries me.

Anyone have any thoughts?

[Eagledriver]

Timing could be way off?

-Andy

[clarelaw]

Yea, that is my thought. Although if it was really way off, I don't think it would start. Right now it is statically time at TDC with the crank and distributor to the #1 cylinder. I'll recheck that, but I am suprised how rough it runs.

I also updated the chain tensioners to the oil fed type. I primed the tensioners before installation, but it is the rattle that bothers me. The 911 are not particularly quiet engines, but the amount of rattle concerns me.

[clarelaw]

Also, it was about 40 degrees outside when I started the engine, although I don't think that would be cold enough to really make it run rough?

[350HP930]

Where does this 'rattle' appear to come from?

[clarelaw]

The 'rattle' sounds like it is coming from the back - rear of the engine. I fear it could be the timing chains, but I cannot fathom how they could be rattling.

[350HP930]

Just to ask the obvious, you pulled the grenade pins on the tensioners, correct?

[clarelaw]

Yes, I thought of that as well.

[Carrera3.5L]

The rattle might just be the forged JE pistons you installed. If so, get used to it. Remember, your stock pistons are cast.

Ralph

[Wayne 962]

Put a timing light on each of the wires to make sure that each is firing. Then, take a closer look at the chains...

-Wayne

[911mot]

Do a compression check too. Is it miss-firing? If so could be something like broken rocker arm or adjustment way out

[clarelaw]

Thanks for all the replies.

As soon as I have the time, I intend to do all of the following before I try to run her again:

1. Pull the oil feed line to the tensioners to make sure oil is flowing to the tensioner. Does anyone think this will cause any problems with air in the line?

2. Pull the valve covers top and bottom and recheck my the valve adjustment and make sure I don't have a rocker arm walking out on me.

3. Recheck the timing to make sure I am exactly timed at TDC - a few degress off could be causing the rough running and back firing

4. Readjust my shifter linkage - I fear when I tried to roll her a bit before, I may have not properly adjusted the linkage and I may have been in 3rd not 1st.

5. If on restart, it still runs rough, then I will test each plug wire with the timing light.

The car has been in storage for over a year while I was doing the rebuild. (9 broken head studs) Part of the rough running may be that the CIS has been sitting for a while. When I reinstalled the CIS I discovered that the prior owner (or some shop in LA) had removed the warm up regulator. I bought the car in LA and she had always been a warm weather car before, so I really didn't miss the warm up regulator. However, the weather here in the Seattle area is a bit colder and wetter. I would appreciate any comments any Seattle locals have as to whether you can get away without a warmup regulator here in Seattle? If I try to run without a warmup regulator (that thing on the left side of the engine right above cyl. 2 and 3 that has two wires to it) do I have to live rough warm ups? Will running without it harm the engine in any way? and, most importantly, will it improve my performance?

[LakeCleElum]

I live in the Seattle area and had a bad WUR for several years. It was a real pain. It would take up to 20 tries to get it started and keep running. Upon take-off, it would run lean, hesitate, and fire back thru the intake for up to ten minutes. I got it sorted recently and it runs great now....I say you really need it.....Good luck...Bob S.

[addictionMS]

sounds funny, but make sure you have the firing order correct, and in the correct direction. I switched from a 3.2 to a 3.0 recently and on first start up I had the 3.0 firing order in reverse, amazingly it ran pretty well, losts of back firing.

FYI 3.2 and 3.0 distributors rotate in opposite directions

Jim

[Wayne 962]

Originally posted by addictionMS
sounds funny, but make sure you have the firing order correct, and in the correct direction. I switched from a 3.2 to a 3.0 recently and on first start up I had the 3.0 firing order in reverse, amazingly it ran pretty well, losts of back firing.

FYI 3.2 and 3.0 distributors rotate in opposite directions

Jim

Yes, I have done this a few times too. 9 broken head studs, I think that's a record. I had seven, I think, and I couldn't find anyone with a story worse than that, until now.

-Wayne

[clarelaw]

Thanks for all the help. I have been letting her sit for a few days. I'll recheck the firing order this weekend. (Mechanic is my night job) I was extremly careful with the rebuild so I don't think it is something major. I know the SC turn counterclock wise, so it is possible that I switched a few plugs. That could easily explain the rough running and back fire.

A new record - lucky me! 5 bottom studs on one side, four bottom on the other. My machinest said that is the most he has seen. Fortunately, they all broke in the middle and were "fairly" easy to extract. Thanks to Waynes book, I was tuning my valves and caught it in time. No head damage, but the engine was an oily mess when I pulled it out.