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MG MGB Technical - Piston ring seating procedure

I've been lurking on this board for a few years now, and usually am able to find answers in the archives for any questions I have, but I can't seem to find info on the following topic. BTW, the advice given here seems to be excellent, and the group here seems to be a great MG family.

So, here goes my first post!

I have just started driving my 73 B after an engine rebuild - which included 10 thou over high compression pistons, a fast-road cam from Colt cams, porting and polishing the head, and balancing. Upon initial startup I ran the engine at around 2000 to 2500 RPM (varying between these ranges) to bed in the cam. I have since put on 300 enjoyable miles, but after the first 250 miles the engine had used 1 litre of oil. Part of this had dripped out of the engine as a result of the side covers being alittle loose and leaky, but mostly the engine appears to have consumed the oil, which I understand is normal before the rings seat.
After talking with one of my fellow MG club members, he suggested running the engine at 2000 RPM in top gear, and flooring the gas pedal until reaching about 50 MPH, and repeating this 2 more times, to seat the rings. Any thoughts on this procedure? I am using 20W50 oil which I planned to change once I reached 500miles.
Also, the first slalom of the season is this coming Saturday - I hope to have another 100 miles on hte car by then - any reason I should not participate? Or should I go easy if I do?

Thanks for any input anyone can offer.

Erick
E.R. Vesterback

Erick,

Interesting thought, but I doubt you can speed up the ring seating much by that procedure.

After a complete rebuild last spring, including a rebore, my engine used a lot of oil. I did just like you have done, 2000 rpm for 20 minutes, and the first 500 miles on straight 30 mineral oil. Then changed to 20W50 mineral oil, which I had to add every time I filled petrol!

Then at about 2600 miles, just as I was getting really worried, oil consumption was dramatically reduced. I am now using about 0,2 litres in 400 miles, and consumption is still sinking.

You probably have to be patient, and perhaps a little careful during that slalom?

Tore
Tore

The advice I was given was to use running in oil (may have been similar to the oil Tore used). This in effect allows more rapid wear, which is what bedding in of the rings actually is - controlled wear so the rings tightly fited the bore. After 500 miles I then switched to a decent 20W50 oil, which should prevent further wear. I also didn't venture over 3k revs for the first 500 miles, except for brief revs in low gear. I would be quite cautious about competing in the car if you have only 400 mile with 20W50 oil behind you. If I were you I'd be tempted to change to running in oil for a further 500 miles and then switch back to 20W50.

Iain
I D Cameron

Erik,
The "wide open throttle" technique you mentioned does work and I have used it on every engine I have rebuilt with no problems to date.

Essentially this loads the engine for a brief period of time and maximises the gas pressure behind the ring to force it against the cylinder wall.

The technique I have used in detail is to have the engine spinning at 1/3 max RPM then run at full throttle until the engine reaches 2/3 max RPM. The idea is to load the engine so the highest practical gear is the one I have used.

Incidently I first found out about this technique from the now sadly deceased Phil Irving who lived at the time a few houses away here in Melbourne.

I subsequently found this is also the method used by piston engined aircraft engine rebuilders with obvious suitable changes.

HTH ,

Cheers , Pete.
Peter Thomas

The wide open throttle method is recomended by the major ring manufactures in this country and is included in their instructions. For some reason the manufactures of parts for our cars never seem to include instructions for running in with their parts.
John H

Back in 82 I had a 1275 midget we rebuilt with .040 over pistons & she used 1 qt of 20-50 castrol oil EVERY 200 miles. After 12,000 miles I sold it to the man that worked with me & he put a oil change on her with 30w non detergent oil & the motor went to a qt every 3,000 miles. I use N/D oil for the first 1,000 miles ever sence & have NO oil users & we have built 100s of motors in the last 24 years.
Glenn Towery

Thanks everyone - I will change the oil to 30wt non-detergent for a few hundred miles, and try the ring seating procedure in 3rd overdrive (4th at 4000 rpm will have me well exceeding the speed limit around here, and there is a serious anti-speeding campaign going on right now).
Erick Vesterback

HI.
I just got this same problem. It was dramatic in oil consumption.
I reopened the engine, take the 4 pistons out to find that the rings were worn out after 2000 miles.
I replaced the original rings with Hasting company rings.
The oil consuption stopped at zero.
Raymond Audet

This thread was discussed between 13/06/2006 and 16/06/2006

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