3.2L Short Stroke Rebuild Complete - A few tuning problems though!

[MBradbury]

HI,

Finally completed the rebuild this last weekend and performed the first r20 minute run-in and oil change. What a relief. Everything appears to work and sounds about right. The rebuild included the gearbox, so glad to find all the gears selected ok. Basically, I only have one outstanding issue, that is a rough idle and burbling (slght backfire) when pushed through the revs. There is no way I could have done this rebuild without the help of Wayne's book and this board, so thanks everyone. I hope someone can help me over this final hurdle, so I will describe the rebuild, etc

The engine was originally a 3.0L SC with CIS. The engine had covered 85k miles and the previous owner had performed a head overhaul within the last 10k miles. When I broke the engine down, it was in remarkable condition. The only signs of wear on the bearings was on the thrust face of number one and one of the intermediate shaft journal shells. All the head studs were in good condition, even the original devlar ones. I didn't start the rebuild because of any issues with the engine. The motivation was more power. After reading many upgrade articles, I decided to go for the 3.2L short stroke. I did all of the rebuild, only resorting to machine shops when I didn't have the equipment. Many parts have been replaced along the way. Here is a partial list...

Mahle 3.2 (98mm) Max Moritz cylinders and pistons (through Andial)
Heads refurbished by Andial (sub contracted to Ollie Engineering). This included, new valve guides and relief machining to allow for the 98mm pistons.
All new mild steel cylinder studs.
Crankcase half faces and cylinder bases flycut, and journal housings align board (Ollie).
Standard SC camshafts reground to 964 profile (Elgin)
New valve train (valves, chains, springs, rockers, rocker shafts, etc)
All new bearings, seals and chain ramps, etc
New fuel injectors and sleeves.
Turbo cam oil restrictors.
New flywheel, clutch assembly, guide tube and completely overhauled clutch operating mechanism.
Gearbox stripped and 1st & 2nd gear synchros and synchro hubs replaced. This was my first gearbox rebuild, so I was particularly chuffed when I could feel all the gears engage.
Many other parts to numerours to list.

In the year prior to the rebuild I also retro fitted SSI headers and a dual in single out SS exhaust.

Engine started first time and ran easily for the first 20 minutes, Which was a great relief, because it confirmed I did the cam timing correctly and at least the pistons didn't slam into the heads on the first revolution.

So far I have driven it around the block and all the gears select 150% better than before. No more preselecting first gear for me.

The only problem is the rough idle and slight backfire when the revs are midly pushed. When I consider the possible causes, I can not discount that the fuel in the tank is about 18 months old, even though I did mix stabalizer in. The other factors are that at 85k miles it must have been retuned to compensate for all the wear in the components e.g. fuel injectors. So, when everything is new, and certain things have changed (964 cams), how do you establish a new baseline? The obvious change is the cam profile. I have set the timing to 5 degrees BTDC with the vacum disconnected. Is this still valid when you have the 964 profile?

Almost there, but I want to clear this last problem before taking it for its second break-in run. Any and all suggestions welcome.

Thanks again.
Mark

[Wayne 962]

Originally posted by MBradbury
The only problem is the rough idle and slight backfire when the revs are midly pushed. When I consider the possible causes, I can not discount that the fuel in the tank is about 18 months old, even though I did mix stabalizer in. The other factors are that at 85k miles it must have been retuned to compensate for all the wear in the components e.g. fuel injectors. So, when everything is new, and certain things have changed (964 cams), how do you establish a new baseline? The obvious change is the cam profile. I have set the timing to 5 degrees BTDC with the vacum disconnected. Is this still valid when you have the 964 profile?

Make sure that you have the mixture adjusted on the lean side - running to rich will tend to lubricate the cylinders and your rings may not seat properly.

-Wayne

[MBradbury]

Wayne,

Played about with the mixture and the air by-pass screw and reset igniton timing to about 8 degrees BTDC. It runs a lot smoother, although I am stll having trouble getting the idle to rise to 900rpm using these adjustments. Currently, hovering around 600rpm and sounds a bit out of balance as a result. I plan to drive it until I burn off the 1/2 tank of old fuel ad then get it set-up at the shop. They have the emissions gear and can set the correct balance, etc.

On a performance note. It's fast. With only 30 miles on the rebuild it revs freely and rockets to 60mph much faster than before. The gearbox is very positive. I now know that 915s can be set-up correctly. Although, renewing absolutely everything on the operating mechanism must have helped. I have a theory that shops mess with these gearboxes without knowing how to align the selector forks etc and that results in poor gate selection. I used the info from the Bentley manual and everything appears to work like a new gearbox.

Thanks again
Mark
1983 SC 3.2L Short Stroke
1988 Carerra (2.7RS Clone Project)

Thanks
Mark

[Wayne 962]

Originally posted by MBradbury
I now know that 915s can be set-up correctly. Although, renewing absolutely everything on the operating mechanism must have helped. I have a theory that shops mess with these gearboxes without knowing how to align the selector forks etc and that results in poor gate selection. I used the info from the Bentley manual and everything appears to work like a new gearbox.

Cool deal - I've got a transmission rebuild book coming in the near future too!

-Wayne

[Doug Zielke]

Originally posted by Wayne at Pelican Parts
Cool deal - I've got a transmission rebuild book coming in the near future too!

-Wayne

The news 915 owners have been waiting to hear!!

[JohnJL]

Any news to share on the transmission book?

[asphaltgambler]

Great applause here for you!! I think that rebuilding the engine and the trans yourself; then having them perform better than before is very satisfying feeling.

Good to see someone that's not in the business take on an ambitious project(s) and be completely successful. That IS what it is all about!!

[rex140@hotmail.]

Grats !!