Valve pitting?

Any topics pertaining to the BMC A-Series engine.

Valve pitting?

Postby Asolepius » Sat Jan 06, 2018 7:16 am

I have the head off the 998 as the gasket blew for the third time. It has been ground flat now - it was warped 6 thou. Now when cleaning up the parts I found what looks like pitting on the seat area of the valves (see photo). This is an exhaust valve, but the inlets also have marks although less obvious. The seats in the head are fine. I have tried lapping but the marks don't go away. However I can't detect any indentations when probing with a pin. Is this really pitting or just discoloration? Am I worrying too much? This head has only done 13,000 miles and compressions were perfect before the gasket went.

As an aside, I am very fed up with failures of new parts. The first head on this engine after the rebuild was a new Metro casting and it cracked in the roof of the centre exhaust port. I then paid £400 for another new Metro head with bigger valves, and that has warped. It really is too much.

Les
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
Joined: Tue Jan 25, 2005 6:50 am
Location: Salisbury, UK

Re: Valve pitting?

Postby Charlie Tolman » Sun Jan 07, 2018 2:22 am

A leak-down test might give you additional information on the valves. (Head on the engine.)

If the cylinder head is on the bench, placing some water or alcohol in a combustion chamber, and looking for fluid seepage past the valve to seat interface, might be a good test.

I would prefer using an old factory head, such as a 12G206 or 12G295, which would have been through thousands of heat cycles, thereby stabilizing the casting to any additional warping.

I raced a 1963 Sprite for 17 years in SCCA, with 948 and 1098 engines, with compression ratios up to 15:1. Yes, the number is correct. For the last 14 of those years, I never had an issue with head gasket sealing or head warping. Of course, the stock head gaskets were improved with careful application of small diameter steel wires. Another factor, was the diligent re-torquing of the head before every track session, usually being four or five times for a two-day racing event. In the usual head nut torquing sequence, each nut was loosened about 1/4 of a turn, and then re-torqued with a steady pull on the wrench, without any stoppage part-way through the pull.

Charlie T.
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: Valve pitting?

Postby Charlie Tolman » Mon Jan 08, 2018 1:42 am

The re-torquing sequence mentioned above, addressed only one nut/stud at a time.
Loosen the nut by 1/4 turn, and immediately re-torque with a continuous (no stopping) pull.
Repeat for the remaining nuts/studs, one at a time.

CT
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: Valve pitting?

Postby Sprimini » Mon Jan 08, 2018 9:30 pm

Thank goodness there is a Charlie on this forum. Otherwise it would be a virtual ghost town. It sure is quiet and lonely around here.

Where did everyone go, Charlie?

What do we need to do to spice things up a bit?

Another question, where and when were you active in SCCA racing?
User avatar
Sprimini
948cc
 
Posts: 55
Joined: Sun Mar 26, 2006 10:06 am
Location: Virginia Beach, Va.

Re: Valve pitting?

Postby Charlie Tolman » Thu Jan 11, 2018 1:29 am

Thanks for the kind words.

I posted a note in the General section of this forum in September, in an attempt to lure people back to our SpriteSpot. The response was not overwhelming.

From 1980 to 1996, I raced a 1963 Sprite in G- and H-Production classes of SCCA, with 1098 and 948 engines, respectively. The highlight was winning the H/P race in the June Sprints event at Road America in 1986. Racing events took me to Minnesota, Colorado, Wisconsin, Illinois, Michigan, Ohio, New York (Watkins Glen), and Georgia. I also participated in the National Runoffs at Road Atlanta in 1985 and 1986.

My home is in a suburb of Minneapolis, Minn., and while I presently do not have a BMC car, I did have a 1957 Austin Healey 100-6 in 1960-61, and a Morris Minor 2-door in the mid-1980s.
The specialty car that now keeps me on the road in the summer is a 1929 Ford Model A sedan delivery (3-door), with a small Ford V-8 engine, automatic transmission, power brakes, air conditioning, and with modified early Ford 15" and 16" spoke-wire wheels.

Charlie Tolman
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: Valve pitting?

Postby Asolepius » Fri Jan 12, 2018 10:33 am

Yes I sometimes think this is just a discussion between Charlie and me!

The marking on the valves I am reliably informed is typical at fairly low mileages these days, and disappears over time. As I said, I could not detect indentations so it seems to be spots of carbon.

I have an old 12G295 which I am sporadically grinding, and hope one day to put on the car. You reminded me of the turbo BMW F1 engine, that used an old production block that sat outside the factory for months. It eventually gave 1450 bhp.
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
Joined: Tue Jan 25, 2005 6:50 am
Location: Salisbury, UK


Return to A-Series (948cc, 1098cc, 1275cc)

Who is online

Users browsing this forum: No registered users and 1 guest

cron