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MG MGB Technical - Bronze VS Steel Valve Guides

I had the head on my 67 B GT rebuild about 15 thousand miles back. The shop that did the head installed bronze valve guides.

On my current engine rebuild, the machine shop doing the machining requested I get steel guides to put back in the head. They said the bronze ones fell out when they took the valves out.

I have read the archives and Steve S gave a good discussion on the pro's of using bronze.

I also see that the shop I am buying my rebuild kit from recommends and uses bronze guides.

The machine shop I am using has a very good reputation with building MG engines, so I am a bit confused as to which way to go.
Bruce Cunha

Hi Bruce

Cast iron guides do not remove heat as well as the correct grade of bronze. Cast iron is self lubricating because of the graphite content which can be a bonus. Not many folk make CI guides, we tend to find the IDs are too big for all the CI guides we have come across lately.
We use CEN CW713R /British CZ135 /USA SAE CA67410/Germany CuZn40A12 2.0550.
It is available off the shelf Stateside and a few places in Europe. We have it made for us in 500Kg batches 5/8ths". If we use an odd size for small OD or larger OD guides batches we use Columbia Metals Colspeed90 which is a derivative aluminium bronze with most excellent wear properties but only about the same as CI for heat dispersal.

Sintered CI guides have better properties than the old fashioned CI guides but I have not seen these for MGBs as the bronze route is preferred.

The fit is dictated by the OD and it may well be the guides were not of sufficient OD to maintain fit in your old head, a problem with sizing not material selection? Some firms try and make it so one can fit the guides then not have to ream the guides to size afterwards. I do not consider this good engineering workshop practice as the guide is held in place by interference which has to be sufficient. This means the ID will suffer as a result and will need reaming to size.

My recommendation would be correct grade bronze guides with correct OD and ID for the job.

Peter
Peter Burgess Tuning

Peter, what is your opinion of K-Line valve guide liners? Most engine rebuilder shops over here stock them.
Mike
Mike Ellsmore

Hi Mike

I may upset a few folk but I do not like them, we have kits to do 9/32, 5/16/ 8mm and 11/32 but seldom use them. It can be useful in Rover V8 ally heads to rectify worn guides and very good in Ford CVH heads where the guides were blanks in the factory then drilled/reamed/seats cut in one op which means the guide od and id are nowhere near concentric. It is really a get you by repair in most applications in my opinion.

Peter
Peter Burgess Tuning

All this is why I won't have my head converted for unleaded unless I really have to.
Paul Hunt

I had my '67 head converted to unleaded, back in the late '80s. They installed nickel seats in the intake and exhaust ports as well as bronze guides. The valves used were stainless steel. The engine still runs like new and I rarely even have to adjust the valves. I'd stick with the bronze guides. Any machine shop, worth its salt, should know by now the proper way to fit them. RAY
rjm RAY

Peter, Your input is most appreciated. The concern I have now is that the top MG engine rebuilder in the area, a person that also races MG's, says the CI are all he is using. He found that the bronze ones typically allowed more oil into the combustion chamber due to the expansion contraction.

I suspect your comment on a lot of this is coming from incorrect machining is correct, but it is a bit of a problem in that there are not all that many machine shops in the area and this one has a very good reputation for MG engines.

My concern is that if I insist on bronze guides, they also will not be done correctly as they use Ci.

May have to look for another shop to do the head. I think I have one in mind and will be talking to the owner tomorrow.
Bruce Cunha

It really shouldn't be a deal breaker if the machinist wants to use CI guides. After all, it's what the factory used and they were the standard of the industry for almost a century. Obviously, he's very comfortable fitting them and has had a great deal of experience with them. The fact that he's sticking to his guns, so to speak, makes him appear to be an honest person with a fair amount of knowledge in his trade. RAY
rjm RAY

I agree with Ray, you should not push the head person. Go somewhere else if you want bronze guides Bruce. Only problem Ray, I am not aware of any CI guides being made the same as the OE ones, may be Federal Mogul? Bruce, we do not run seals on race Bs we are happy with some guide lubrication esp down ex guides. We get a puff of oil when engine does a hot start (oil in ex guides) then no visible oil. Each to their own but remember, what is used for a Race B is not necessarily that which is used for road or even track day fun use. The correct bronze guide will take heat away better than the CI and better than thin wall liner.
We use seals on all B applications except Race (MSX heads have to have seals for all applications).

Peter
Peter Burgess Tuning

"I rarely even have to adjust the valves."

Since I discovered that some of my valves were still changing gaps at the strict 'rule of nine' point, so started checking/adjusting at the point of maximum gap, I haven't had to adjust mine at all. Until I changed the head gasket, that is, it wouldn't surprise me if they needed closing up a smidgen at the next service.
Paul Hunt

Had a good conversation with the machinist doing the head. He gave his explanation for his use of CI inserts.

The shop is in California. Because of air quality regulations, the gasoline used in California is different than any other in the US. According to the Machinist this gas results in different temperatures in the combustion chambers and this makes it more difficult for the expansion and contraction of the bronze guides. he said that anywhere else, bronze works great, but he has had a lot of problems with heads done in bronze that run in California. This applies to all the engines he does, not just the MG engines.

Sounds like there are no downsides to CI inserts, just a but more upside for bronze.

Bruce Cunha

Bruce, I've been running my B, with bronze guides, in California for almost twenty years with no ill effects. I've never experienced a seized valve or any other problems either. I run my engine hard every time that I take the car out for a drive. The car likes it and performs accordingly. I do all of my own maintenance and repairs and keep a close eye on everything serviced or replaced. I have records on my computer, going back to '83, when I wrote a program in BASIC to keep track of my car and those of my customers.
Paul, I too have experienced a variation on the rule of nine and rotate the cam accordingly to find the spot with the most clearance when adjusting the valve lash. RAY
rjm RAY

Hi Bruce

The bronze we use takes heat away at about 2.5 x that of CI, wear rate is far lower in the bronze we use. If we do get a nip from overheating the guide usually lets go of the nip as it cools and no visible damage is to be seen. With CI any seizure and there is a lot of gaulling damage. I do not see why California has different fuel from all the rest of the world? We have very hard raced engines running on minimal quality fuel with no ill effects.

Does the California machinist remove OE bronze guides in BMWs, Mercs, Audis and replace them with aftermarket CI ones?

Peter
Peter Burgess Tuning

"I do not see why California has different fuel from all the rest of the world?"

My understanding is that it has been significantly different from the UK for many years. They went unleaded in 1975 whereas we didn't go until 1999, and at about the same time got 10% ethanol. They are now getting 15% ethanol, when in practice we haven't seen 10% yet, and there is argument as to whether the higher octanes have any yet.
Paul Hunt

I know we have different fuel from USA and ours is getting worse, I was just asking if California is different from rest of USA and maybe rest of the world? Some of the worst fuel we have come across is Tibet area with the Paris Peking rally!

Peter
Peter Burgess Tuning

Nope, California has the worst fuel around. Every year, somebody introduces a bill, in the state senate, to make it even worse to lower emissions in the big cities. I have to run an ignition retarder, with the supercharger on my engine, just to keep the engine from pinking on steep grades. Catalytic converters, which are legal in all other states, are not legal in California. Hitler would have have loved it here! RAY
rjm RAY

:) Ray

Just need to know if that machinist has problems with the OE VAG Audi, Merc, BMW bronze guides (basically same material as we have made, which we unashamedly copied from USA material. We had loads of material analysed years ago and that came up as the best, interestingly the Special Tuning factory bronze was the worst and the bronze liners didnt score that well either. The Austin champ/gypsy engine had factory fit bronze guides, these were quite good and came about the same length as MGC ex guides and were same OD and ID, we used to shorten these and use them in race Bs till the source dried up and we moved on to our own guides for all spec heads, both a and b series around 1989 (info on bronze guides courtesy of Don Loughlin of Aldon fame). We run the guide clearances with out bronze the same as standard factory CI guides. A note of caution, sometimes valve stems can vary on aftermarket valves (inc race valves) so the clearance may have to be opened up to suit.

Peter
Peter Burgess Tuning

This thread was discussed between 11/09/2014 and 24/09/2014

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