Break-in procedure for rebuilt engine?

[Brotok]

What is the proper procedure to break-in a rebuilt engine with a valve job?

I just rebuilt my '79 911 SC's motor, I ground the seats and valves as part of the job, replaced all bearings, rings etc. I'd like to know what the experts here recommend for the break-in procedure and I'd appreciate comments on the following:

1. When should I change the oil?
2. When should I re-adjust the valve clearance? After a valve job, Porsche recommends adjusting the valves to 0.25mm, running the motor for 30 minutes and then re-adjusting the valves. I set the clearance to 0.25 mm but feel that 30 minutes is not enough time and plan to log about 1000 miles on the engine before re-setting the clearance to 0.1 mm.
3. How should the car be driven during break in?
4. When can I feel free to let her out?

By the way, the engine runs fantastic - a lot more power, response, better sound, etc. This board has been tremendously helpful in the process, I am truly grateful for all your help.

Thank you.

[Wayne 962]

I've got a whole chapter on this in my Engine Rebuild book, http://www.101projects.com

Too much info to simply repost here...

-Wayne

[Brotok]

Thank you for that reference. I am sure that the book has all the answers that I am looking for, but ordering and reading the book for the relatively few pieces of data that I need does not seem practical at this point. All I really want to know is how long one should wait to adjust the valves and at what intervals should the oil be changed during break in.

[sp_cs]

Congrats on the completing the rebuild Brotak.

My 3.2 (now 3.4) is circa 3k miles post rebuild - my mechanics advice was to limit revs to 4k for first 500, extend to 5k for next 500 - then change oil and check valve clearances.

I performed an intermediary oil/filter change at 500 using 15/40 dino oil - then changed to Motul 5/40 synth at 1000.

Cheers

Edit - was also advised to vary the revs during the first 1000 miles - ie no constant revs eg motorway/freeway runs - plenty of varied acceleration and deceleration. And no loading the engine - keep it in a low gear to keep the revs up

[chrisp]

I would get the book. It helped me tremendously when I put my shop rebuild back in my car. You have a lot invested back there (time & money) why risk it on saving $23 and a few days of shipping.

Plus, it helps support this free forum.

[porschenut]

Originally Posted by Brotok

After a valve job, Porsche recommends adjusting the valves to 0.25mm, running the motor for 30 minutes and then re-adjusting the timing. I set the clearance to 0.25 mm but feel that 30 minutes is not enough time and plan to log about 1000 miles on the engine before re-setting the clearance to 0.1 mm.

I'm certainly no expert in these matters, but I find it amusing that you plan to ignore the advice of the brilliant Porsche engineers that designed your engine, and instead go with your feeling. If it were me (and it will be someday), I would follow Porsche's instructions to the letter.

[Zeke]

Not enough info here. New (or reground) cams? That changes the break-in procedure. No new cams, you need to stand on the gas, but not over rev. This will seat the piston rings. Many will simply find a stretch of road and go up and down the gears 4-5 times. After the rings are seated, take it easy for the 1st 1000 miles or so.

Again, some will change their oil after cam and ring break-in and then again at 1000. High revs wear an engine faster than anything else. You don't want to break in an engine by wearing it out.

Otherwise, I agree with sp_cs

[Gunter]

Originally Posted by Brotok

What is the proper procedure to break-in a rebuilt engine with a valve job?

I just rebuilt my '79 911 SC's motor, I ground the seats and valves as part of the job, replaced all bearings, rings etc. I'd like to know what the experts here recommend for the break-in procedure and I'd appreciate comments on the following:

1. When should I change the oil?

After 1-300 Miles plus new filter

2. When should I re-adjust the valve clearance? After a valve job, Porsche recommends adjusting the valves to 0.25mm, running the motor for 30 minutes and then re-adjusting the timing. I set the clearance to 0.25 mm but feel that 30 minutes is not enough time and plan to log about 1000 miles on the engine before re-setting the clearance to 0.1 mm.

Would love to see more info on the recommendation for 0.25mm and re-adjusting the timing? Ignition timing?

3. How should the car be driven during break in?

No high-revving past 4k. Did you rev up and down during the 30 minute ring-seating procedure?

4. When can I feel free to let her out?

After about 1k Miles

By the way, the engine runs fantastic - a lot more power, response, better sound, etc. This board has been tremendously helpful in the process, I am truly grateful for all your help.

Thank you.

1000 Miles with 0.25mm Valve clearance? Is that reliable info from Porsche?
Surprised you didn't get Wayne's book; a fantastic help for a rebuild.

[Brotok]

Thanks for the replies. I replaced the cams with a set of stock used SC cams, replaced a few rockers too with used ones - does that require break-in?

I made a typo in the original post (now corrected): Porsche recommends re-adjusting the valve clearance after 30 minutes, not the timing - my apologies. This is in a short paragraph on page E79 of the workshop manual, and pretty much states what I have reproduced here.

I didn't really do a 30 minute ring break in like most recommend, I just went out for a ride about town where I did accelerate and decelerate a bit since I heard that that's what is advised. Have been keeping the car below 4,500 rpm. occasionally let it go to 5,000 rpm.

The reason I am not getting the book is neither money nor impatience and I have given plenty of support to our host through purchases. Rather, this car is currently my only transport and I will have to start driving it on Monday.

There is some logic behind ignoring Porsche's recommendation to re-adjust valves after 30 minutes of running the engine, and I doubt that this would be the first time that Porsche's recommendation is controversial. The logic follows:

- It is dangerous to run valves that are too tight, e.g., tighter than 0.1mm
- It is not dangerous/harmful to run valves a bit too loose, e.g., slightly less than 0.25mm (actually, 0.25 is the clearance used on many BMWs for normal operation).
- Valves only get tighter as they pound into the seat after a valve job.
- By adjusting valves to 0.1mm before they have had a full opportunity to sit, there is a risk that the valves will continue to sit after adjustment and become to tight, hence, harmful.
- By postponing the adjustment to 0.1mm we are reducing the risk of running on overly tight valves and not harming anything in the process since slightly loose valves are not dangerous.
- So, to me it just makes common sense to let the valves pound longer than Porsche recommends before adjusting them.

Does anyone agree?

Thank you for bringing all of this up

[jpnovak]

I am in the same process. here is my method for a top-end rebuild with new cams, rockers and complete head work.

Break in the cams at 2100 rpm for 20 minutes. Wait another bit of time until the thermostat opens on the oil cooler. Shut down engine and drain oil.

Next day, go for a drive. I went to the store for gas and back. This is to just warm up the car. Upon return check the car for leaks. Make sure to monitor all gauges. I have an external EFI with more information and I find this helpful.

After the initial drive the car should be warm. Go and and drive it hard. I found an empty road with a decent speed limit 55. Put the car in 3rd and pull from 2500 to 5K with lots of load. Foot down until the revs come up then let the engine brake itself down. Downhill engine braking works great. High load up the hill, engine brake down the backside. Rinse, repeat. After about 30 minutes I increase the rev limit to 5500 and to 6K after another 30 minutes.

The next day, drive again the same way. I am a believer that engine braking down a hill is the best way to seat rings. Going up the hill creates high load to push down, and out on the rings. Down the hill creates high cylinder vacuum pushing up and out on the rings.

At some point you should notice the engine is starting to have more pressure to the engine braking. The feeling is that the engine has more ability to slow you down when you take your foot off the gas. When you feel this your rings are breaking in.

Mine took about 2.5 total hours of driving to get the feeling.

YMMV

[JBO]

If you replaced the P & C's, or re-ringed them, then you need to be careful to follow the procedures. If you reused your P & C's due to relatively low mileage, then you don't need to do much special.

[Zeke]

Originally Posted by Brotok

Thanks for the replies. I replaced the cams with a set of stock used SC cams, replaced a few rockers too with used ones - does that require break-in?

Most would recommend that any cam swap be done with a light regrind and the rockers reconditioned, which is resurfacing and hardening. Rockers are supposed to be kept with the lobe they ride on. If swapped around, they should be reconditioned along with the cams. This, then, would require a 20-30 min break-in.

If you didn't install new or reconditioned parts, you would proceed to the ring break-in. However, I would watch the valve adjustments very carefully. If any need frequent adjusting, the cam may be going flat due to uneven contact with the rocker.

[Gunter]

Originally Posted by Brotok

I made a typo in the original post (now corrected): Porsche recommends re-adjusting the valve clearance after 30 minutes, not the timing - my apologies. This is in a short paragraph on page E79 of the workshop manual, and pretty much states what I have reproduced here.

Does it actually say in the workshop manual to adjust the valves at 0.25mm for a break-in?

There is some logic behind ignoring Porsche's recommendation to re-adjust valves after 30 minutes of running the engine, and I doubt that this would be the first time that Porsche's recommendation is controversial. The logic follows:

Nothing wrong with checking the valve clearance per recommendation but I cannot buy into setting them two and a half times normal clearance

- It is dangerous to run valves that are too tight, e.g., tighter than 0.1mm
- It is not dangerous/harmful to run valves a bit too loose, e.g., slightly less than 0.25mm (actually, 0.25 is the clearance used on many BMWs for normal operation).

Appels and oranges. Different engine, cams, overlap. Valve-lash for exhaust valves is more critical than the intakes but 0.25mm is not just a bit loose, it's over the top. Did you time the cams with 0.25 or 0.1mm?

Does anyone agree?

Anyone ever went with very loose valves for a break-in?

Thank you for bringing all of this up

Input, please.

[Brotok]

Originally Posted by Brotok View Post
I made a typo in the original post (now corrected): Porsche recommends re-adjusting the valve clearance after 30 minutes, not the timing - my apologies. This is in a short paragraph on page E79 of the workshop manual, and pretty much states what I have reproduced here.

Does it actually say in the workshop manual to adjust the valves at 0.25mm for a break-in?

In the valve job section of the workshop manual it says to adjust valve clearance to 0.15 mm in excess of standard adjustment for bedding in the valves, and to run the engine for a 30 minute test run before re-adjusting to standard clearance.

There is some logic behind ignoring Porsche's recommendation to re-adjust valves after 30 minutes of running the engine, and I doubt that this would be the first time that Porsche's recommendation is controversial. The logic follows:

Nothing wrong with checking the valve clearance per recommendation but I cannot buy into setting them two and a half times normal clearance

- It is dangerous to run valves that are too tight, e.g., tighter than 0.1mm
- It is not dangerous/harmful to run valves a bit too loose, e.g., slightly less than 0.25mm (actually, 0.25 is the clearance used on many BMWs for normal operation).

Appels and oranges. Different engine, cams, overlap. Valve-lash for exhaust valves is more critical than the intakes but 0.25mm is not just a bit loose, it's over the top. Did you time the cams with 0.25 or 0.1mm?

I agree that BMW and Porsche engines are very different but I still do not see the harm that could be caused by opening valves slightly later, and I don't imagine that 0.25 mm is so much space for rockers to bounce around as to cause damage. On what do you base your conclusion that 0.25 mm is over the top? I timed the cams at 0.1 mm of course.

Does anyone agree?

Anyone ever went with very loose valves for a break-in?

Thank you for bringing all of this up

Thanks to everyone for their input