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MG MGB Technical - 5 Main/Valves
|Hello,I am getting ready to put my 1972 mgb roadster engine back togather,its been hot tanked,new pistons etc. Question:I had thr orginal valves ground,lapped,etc,would you put new valves in or use the orginial ones?Anyone fimilar with the " stellite" valves that vic.. British sell?Thanl for the advice,Rich O|
Unless you've had unleaded valve seats installed, you'll surely have a problem with the valves receeding into the head. Reuse 33-year-old valves? Err, I'd suggest that the ones with stellite tipped valve stems made of Austenitic Stainless Steel will hold up best under the high temperatures generated by unleaded fuel.
|Steve,My old valves have 58,000 miles on them.Never thought about the gas of today.I would be still using a lead additive in her,any thought ?Thanks,Rich O|
|Right, the original valves will be fine. Are the guides OK. Personally I would have have hard seats installed in the head and three angle cut by the machine shop. If the guides are OK that's fine but if they are worn then the shop will replace before installing the inserts and cutting the seats. No need and even underirable to use bronze guides. |
You can now use unleaded fuel.
|Iain,thanks.What are you refering to as the "inserts"? and the hard seats?Correct me if i'm wrong,does the valves have to be matched to the seats?Like you cant just grind the valves without (grinding)the seats?Is it okay to reuse the valve springs?I need to place an order and want to get all the thing that the machine might need.Doubt that they can get this stuff locally.Thank once again ,Rich|
The majority of additives sold on the North Americn Market as "lead substitutes" are snake oil. I wouldn't trust any of them to protect my valves and seats. If they were effective, there would be no market for hard seat inserts. In using the terms "inserts" and "hard seats" we are refering to the same thing. These are seats specially made for use with unleaded fuel. Yes, once they're installed they will need to be machined so that they're sealing surfaces will match those of your valves. You would have to have the seats remachined even if you didn't install them. Iain recommends that you have both the seats and the valves modified to make use of a three-angle configuration. This will give you about a 10% power boost on the cheap. Reusing old valve springs is a chancy business. You have no way of knowing if the speedometer in your car didn't come out of a wreck to replace the original after it died of high mileage. Even if the shop tests the valve springs and says that their poundage is still within factory specifications, one of them may be ready to break from metal fatigue. You're going to have to face up to the reality that a head rebuild is not something that a wise person tries to economize on. Fools do, however, and they pay the price when a burned valve gets sucked into the engine, usually on a lonely country road on a rainy night (Murphy's Law!) Of course, they can also get stuck out there when the head gasket blows because they were too cheap to get the head skimmed flat and pay a little extra for a Payen head gasket!
|Rich, the inserts are hardened pieces of metal pressed into the head to replace the soft cast iron valve seats. They will increase the life of your head and valves while allowing you to use unleaded fuel. A valve job would be necessary at the same time. The whole works should be from $250-300 and any decent machine shop can do it. It WILL give you a good power boost. |
I'd also consider new valve springs, but don't just go buy a cheap set. They could be worse than the old stock ones, which I guarantee have lost considerable strength from repeated heat cycles over the years. Look for a good quality replacement SET with stock pressures - not the high rate performance units designed for modified cams. If you have to purchase 8 separate springs, they will invariably be from different batches with different spring rates, so only buy them as a set. Double springs are a very good idea!
|First, it is nice to see Steve S. back for a visit. Hopefully, he will have more time to share with us in the future. |
Secondly, like Rich, I expect to be rebuilding a pre-unleaded engine this winter. Thus, some of his questions are also mine.
I understand the need for hardened valve seat inserts to be put into the head. It keeps the exhaust valve from sticking to the cast iron and forming a series of "quick welds" which are ripped loose the next time the valve is operated, resulting in both damage to the unmodified seat and the valve. The unleaded gas cylinder heads used an induction hardening of the valve seat area to make a "hard seat".
Were the exhaust valves made of the same material throughout the production life?
If so, can we expect the standard exhaust valves to last the 100K that they did on the RB car engines before having to worry about replacement?
If the standard valves will hold up, for "average driving" (including long trips), as the engines did when the came from the factory, what is the advantage of upgraded valves except in a racing/rally car?
Last, Jeff recommends the purchase of valve spring sets rather than the purchase of individual spring. Who is producing sets of springs and what is their stated tolerance from spring to spring?
As a last item, valve guides come in cast iron and silicone bronze. Comments on your experience with either/both types would be worth hearing again and what, if any benefit there might be from using the more expensive silicone bronze on a driving car vs. a race/rally car.
|Rich, Most of the questions have been answered by the time I got up but just a bit more clarification. Sorry for confusing you with inserts and hard seats. In effect the insert material provides the material for the valve seat and will prevent head recession in the future. The guides must be good, as the seat cutter locates in it and then cuts the seat concentric. If the guide is not 100% then the seat will be all over the place. Now there has been much said about bronze guides on this and the MGA forum and it seems that sticking valves do happen. My head reconditioner who races cars says a definite 'no' to them because of short life. In any event, modern production cars dont use them and seem to run perfectly well. Yes the bronze may transfer heat just that bit better but I have run my Bs for 7 years now on unleaded without any problems.|
The three angle seat will give you a bit more performance for free so it seems a pity not to take it. The original valves don't need modified in any way, just grind them in. Of course if they have a burn then the reconditioner can neither reface or replace as necessary. To test that a valve is properly ground and seating put a series of pencil marks round its circumference across the valve seat, replace the valve and turn it in the seat. All the pencil lines should be smeared. Then turn the head over and drop all the valves in (no springs) fit the spark plugs and pour some white spirit into the chambers. No fluid should get into the ports.
My machine shop charged me £20 per insert and cut.
|Les,Jeff,Steve,Iain,Thaks for the discussion,However noone has said where you can get the "harden seats",the "matched spring set".I guess where i"m comming from is that i orginially have always owned this car,i know the exact miles on it(it had 10 miles when i bought it)she has sat for 20 years in a heated garage.I /my wife ,all we want is to restore it new like condition,and be able to drive is on short(like 150 miles or so)type trips in our future retirement years.She(car)is a regular gas user now,where/what do i do based on the above infomation.If i need "seats" "springs" ,can they be gotten from MOSS,Vic. British.???????Does anyone have any part number from where to order these things.I'm new to the motor business,but i do have a 28 year mechanic veteran (work at a G.M dealership )who is a close friend that can help me do the work.Thank,much to everyone,and I DO NEED YOUR HELP and ADVICE.Rich O|
Your machine shop who is doing the block work can advise you as to whether you need to replace anything in the head. If they have already ground the valves, then it would appear that they think it's OK. Most important is to have acceptable guide-stem clearance, new stock guides are cheap, but need to be replaced BEFORE seats are ground. All the above talk is OK to a point, but if your original stuff is passed by the machine shop, you should be good for another 50,000mi in normal use. Boy-racer dreams, sky-is-falling worrywarts, theoretical ideals, and people with too much money are not good guides to reasonable action. I, too, can think up all the preceding ideas, but for real people with real cars, I would expect that a reasonably maintained 58,000 mile B head should be OK with nothing other than maybe replacing guides, regrinding valves and seats, and correct assembly. Given the many reports of bad aftermarket parts, I am increasingly inclined to not replace anything that doesn't NEED it. I've done a lot of heads to "less than ideal" state, due to lack of owner funds, and the're still out there and running fine. In any event, the head comes off easily if a problem develops, and the stock springs and valves are not prone to catastrophic failures, even at this age and mileage.
|FR Millmore<thanks for your advice,what do I do about the Regular gas situation,can it i use unleaded or what??????Rich O|
|Unleaded is what we have, most folk are just running it with no additives and no problems. You can get seat recession if the car is run hard for long periods of time, or hot for any reason. Keep the valves adjusted properly. But, if you do develop this, the worst that can happen is that you have to pull the head and fit hard seats; meantime, you may well get a lot of miles on the existing parts. If this becomes necessary, then by all means fit the hard seats with new valves and guides at that point. The machine shop doing the job will be able to procure the seat inserts and guides - let them, as the whole job is then their responsibility. Stellite faced exhaust valves are great, when it comes time; valve springs are normally sold in sets and will be adequate for normal street use. From what you say about your driving intentions, it will be a long time from now.|
|I agree. Don't waste your money now with hardened valve seats. It was gloom and doom when leaded disappeared and everyone was advised to get hardened seats or else. The predictions were untrue and most cars suffered no damage from the unleaded gas, including my Datsun.|
However, I would not have any exhaust seals installed as the new 'ethanol' blended gas is playing havoc with valve stems and guides. Several race builders as well as others will not install seals anymore on the exhaust valves because of the lack of lubrication - my car is living proof of wjhat can happen when my valves galled to the guides for lack of lubrication.
|I ran a Rover at one time mid 80's which was supposedly not suitable for unleaded fuel. I used unleaded in it from the word go and put 80k miles on it without a problem. Then again it was a company car and these are intended for misuse !!|
Having the head off the B I personally would fit hard seat inserts so that I was sure that I wouldn't have to remove it again. That's what I did on both my Bs. I fitted nothing else new and they both run very well. It's very much a case you pay your money.....
|Iain and Mike,|
All cars with aluminum heads already have inserts, and they are virtually all suitable for unleaded. The inserts are about the same alloy as the "hard" inserts installed in the conversions. "Hard" is a bit of a misnomer - induction hardening is a way to cause cast iron heads to have good seats, the inserts rely more on the metalurgical characteristics of the insert.
|F.R.Millmore,you for the first time just totally lost me in the last post.Rich|
Sorry! The cars referenced by Iain and Mike probably have aluminum heads, don't know for sure, but I think all Rovers and most Datsuns since the 60s did. They have seat inserts, generally made of a high nickel steel alloy. Most of the "hard" inserts used in unleaded conversions are similar, but they are not really hard. Cast iron can be hardened by intense local heat, usually done by induction hardening - high frequency electricity - or flame hardening. This was done by factories to make seats (in cast iron heads) suitable for unleaded fuel when it became the norm. These seats are REALLY hard, hence the term. I think BL used this process on later cars (80-on??), don't know if any of the US cars had it done from the factory.
| Hi FRM,|
It must put a high contraint into the head to harden cast iron heads valves seats in such way. Any way, I guess it's a matter of cast iron quality and 60's quality was a bit fair because of high carbon ratio ?
Yes, seems a bit drastic, but it has been done for years on heavy duty engines. General Motors did it on their iron heads when unleaded came in, and the process is also used to harden ways on machine tools, etc. Does anyone know when BL started? It would seem that they should have done by 75, at least for US cars. Come to think, I don't recall doing a valve job on a post-75 car that still had it's original head.
|Fletcher, yes the car had an ali head which would have been inserted but the vehicle had specific instructions that it was not suitable for such use. Two years later a U/L head conversion became available but I never purchased this option on the basis that it would make economic sense to wear out the original seats before conversion. This never happened. However having an engine in pieces I personally would always convert a head for U/L use prior to reassembly. And who said the Scotsman was tight fisted??|
Even the factories didn't know what was going to happen with unleaded, gloom & doom were predicted at every level!
Yon Scotsman while gnashing his teeth at the cost of upgrade is far sighted and cheap enough to expect the engine to last forever! Me too, but I figure why not wear it out, then fix it? I would certainly fit inserts if I had a head with worn-out seats, or if I expected to run it hard, but most people on this side of the pond don't actually use the cars, just piddle about a bit in the summer. I have customers who manage to put on only a few hundred miles a year, and who go bonkers if I take them out and get it over 3500rpm. That represents the majority, Sad but true! Under those conditions, they will last beyond the owner's lifetime without wearing out the original seats.
|This is all so true as well. I happen to have a heavy right boot so don't want to take chances, You are also correct in that Rover didn't know what they were fitting and whether or not it would stand up to constant hard use. It did. Not so sure about cast iron though that's why I go for the inserts.|
This thread was discussed between 27/08/2005 and 01/09/2005
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