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 Posted: Mar 16, 2017 03:35PM
Total posts: 213
Last post: May 22, 2017
Member since:Oct 8, 2012
Camshaft.....Not sure, but I'm in the process of breaking down the engine. Just got off the flywheel. Tomorrow night I can pull the cam and check it out. Rockers, nothing special.....OEM I think. Does all this play into what springs should be on the head? Thanks for confirming the head thickness, sounds like 2.750 is probably a good starting point. Mine is down to 2.711 I think.

 

MightyDog

 

 Posted: Mar 16, 2017 11:58AM
Total posts: 3258
Last post: May 21, 2017
Member since:Feb 26, 1999
Quote:
Originally Posted by DyeLooper
So I'm working on rebuilding my head on a 1275. The head that came on the car was a 12G940 head with 1.15"/29.3mm exhaust valves & 1.3"/33mm Intakes. I have replaced the guides & seals. The springs that were on the car were the single spring at 52mm length, sold her from our sponsor.        http://www.minimania.com/part/12G1015/Austin-Mini-Single-Outer-Spring-For-All-A-Engines-998-And-1275

I am not finding an information for these springs. 
Q
uestion. My old springs, are they still good? Does anyone have a valve spring chart? At the valve seat, what is the pressure? When compressed to a certain length the pressure is? Not finding anything for these springs. Also, 12G940 head thickness. I found somewhere the starting thickness should be around 2.750" ? Correct? Wrong? Is there a minimum it can can be shaved to?

Anyhelp would be appreciated
As you ask about the starting thickness I can go along with the 2.750".  Checking 5 of the 12G940 heads I have three of them were in that range (2.750", 2.753", 2.750") the other two one was 0.020", and the other was 0.080" shorter.  AS for the springs several factors enter in here.  What cam are you using? What rocker ratio are you using?

 Posted: Mar 16, 2017 08:17AM
Total posts: 8405
Last post: May 23, 2017
Member since:Jun 5, 2000
US
I sort-of follow what Steve suggested.  However, I will clean the head and do some port match grinding.  If I want to put bullet nosed guides in I will machine and install them.  However, I leave all the seat cutting and valve grinding to the machine shop.  Before I spend any time on the head I will take it to the shop for leak and crack testing.  It does mean multiple trips to the machine shop but it can be worth it.

I like Steve's quick screening check on valve springs by height.  That makes a lot of sense.

Doug L.
 Posted: Mar 16, 2017 08:11AM
Total posts: 213
Last post: May 22, 2017
Member since:Oct 8, 2012
"Excuse the ramble, what spring pressure are you shooting for? Steve (CTR)"

No rambling......It's all great information, thanks Steve. Although I did not mention it, I do work in a machine shop. BUT, working on the engine is new to me. I am having a local very good shop take care of the head for me. And he's asking the same, "what spring pressure are you shooting for"......I'm really suprised that from all the years, there is not a set specification of what the spring rate should be for a specific spring on a specific valve on a specific head. Or is it all up to ????

 I did get from Don Racine, with the springs I would be replacing, since that what was on there to begin with http://www.minimania.com/part/12G1015/Austin-Mini-Single-Outer-Spring-For-All-A-Engines-998-And-1275     

At 1.320"fitted spring length the seat pressure is 70lbs, although he likes to target 80lbs.   

 

MightyDog

 

 Posted: Mar 16, 2017 07:46AM
Total posts: 3353
Last post: May 29, 2017
Member since:Oct 8, 2011
US
As a machine shop guy for many years I'd not suggest people do their own head work. Our basic cyl. head valve job includes. Strip cyl. head, wire brush chambers and ports, mag. for cracks, check guides, surface, stem wear and valve head margin, check springs for equal length. Clean head and all parts in tank. Glass bead valves and wire brush. If valves are good grind in centerless grinder and tip. Install valve guides as required. Machine three angles on valve seats in head. Setting all valve seats at same height with seat in center of valve face. If all springs same height check a couple and assemble head with new seals, vacuum check all valves and ports. Bag and call customer.    -+

Setting valve seats at same height makes getting spring pressure easier. I had a spring seat cutter made for facing the spring seat in the heads. 

I realize there are people who will not agree with me about doing your own. I will say having been in the biz for 25 plus years retiring 17 years ago, I currently use five different auto machine shops to build engines. Each has either a person or equipment that make the drive worthwhile. 

Excuse the ramble, what spring pressure are you shooting for? Steve (CTR)

 Posted: Mar 16, 2017 05:59AM
Total posts: 213
Last post: May 22, 2017
Member since:Oct 8, 2012
Doug......The specs for the springs I want to use is the information I am looking for, can't seem to find it. I'm pretty sure some has been shaved off all ready. Just wondering what is to much, thought I remember seeing in the Haynes manual no greater the .080"


Steve......The new guides are in and we will be turning the seats to match up with the new center line. Awaiting a new cutting tool. Still searching for some specs on the springs. Supposed to be 52mm free length, I'm measuring 51-51.9 on assorted springs. To much difference in your opinion?

 

MightyDog

 

 Posted: Mar 16, 2017 05:25AM
Total posts: 3353
Last post: May 29, 2017
Member since:Oct 8, 2011
US
A lot of heads are marked 940 and some are already lead free. I have had to start having all my heads converted to hard exhaust seats. Cars with limited use may not need them but you never know. After doing quite a few heads I had one come back due to valve seat wear. You mention replacing guides and seals. I hope you had this done at an auto machine shop. Changing guides moves the center line of the valves and the seats need cutting to match. I don't like reusing valves as the margin after regrinding is so thin. Once all guide, valve and seat work is done I CC the chambers and with this info and piston to deck figures on the block I can have the block surfaced as well as the cyl head to reach the CR I'm looking for. Springs are best if the lightest pressure that will do the job is used. I have a spring tester but I first line them all up and place a straight edge along the tops. If all the same height they are most likely OK. A bad spring will be shorter not much but measurable. 

I currently have three Jap spec AC minis up in the air at the shop. Also have a mid 80s  Mayfair  getting a fresh power unit all suspension and brakes. As for the AC cars one is getting freshened with a Swiftune 1293, the other a Calver 1293 and the last a 1293 Completely built in shop. Two are also auto to std tranny conversions. On yeah I forgot I also have another classic getting a 1400 cc power unit replacement. All have hard valve seats and springs matched to the cam of choice for each. Steve (CTR)

 Posted: Mar 16, 2017 03:58AM
Total posts: 8405
Last post: May 23, 2017
Member since:Jun 5, 2000
US
Quote:
Originally Posted by DyeLooper
So I'm working on rebuilding my head on a 1275. The head that came on the car was a 12G940 head with 1.15"/29.3mm exhaust valves & 1.3"/33mm Intakes. I have replaced the guides & seals. The springs that were on the car were the single spring at 52mm length, sold her from our sponsor.        http://www.minimania.com/part/12G1015/Austin-Mini-Single-Outer-Spring-For-All-A-Engines-998-And-1275

I am not finding an information for these springs. 
Q
uestion. My old springs, are they still good? Does anyone have a valve spring chart? At the valve seat, what is the pressure? When compressed to a certain length the pressure is? Not finding anything for these springs. Also, 12G940 head thickness. I found somewhere the starting thickness should be around 2.750" ? Correct? Wrong? Is there a minimum it can can be shaved to?

Anyhelp would be appreciated
Sorry, no comment on your new springs.  Whether your old springs are still OK is not easy to answer either.  Springs do wear out and they do break.  You can measure the force at a given amount of compression and determine the spring rate (pounds/inch).  That value can then be compared to published specs to tell you something about the condition of your old springs.  However, knowing the spring rate of old springs does not give an indication of how likely they are to be near the end of their fatigue life.

I also don't know the initial thickness of a 12G940.  However, with compression limits imposed by the octane ratings of today's fuels, it is unlikely you will find it necessary to shave too much off the head.  

Doug L.
 Posted: Mar 15, 2017 01:08PM
Total posts: 213
Last post: May 22, 2017
Member since:Oct 8, 2012
So I'm working on rebuilding my head on a 1275. The head that came on the car was a 12G940 head with 1.15"/29.3mm exhaust valves & 1.3"/33mm Intakes. I have replaced the guides & seals. The springs that were on the car were the single spring at 52mm length, sold her from our sponsor.        http://www.minimania.com/part/12G1015/Austin-Mini-Single-Outer-Spring-For-All-A-Engines-998-And-1275

I am not finding an information for these springs. 
Q
uestion. My old springs, are they still good? Does anyone have a valve spring chart? At the valve seat, what is the pressure? When compressed to a certain length the pressure is? Not finding anything for these springs. Also, 12G940 head thickness. I found somewhere the starting thickness should be around 2.750" ? Correct? Wrong? Is there a minimum it can can be shaved to?

Anyhelp would be appreciated

 

MightyDog