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MG MGB Technical - Rebuild time - what to do?

I also posted this at MG Exp too, as it's a big decision!

With the engine being pulled to properly replace a blown head gasket / skim the head etc...the question is - how far to go? I realise this is an open question, but the more opinions the merrier. While money is of course a consideration, with things apart, what would be some nice, good dollars-per-horse things to consider?

The aim for this car is a nice street car / daily driver, so no race cams, thanks, but who could say no to a few more gee-gees?

Here's my list, with thoughts in brackets. Approx dollars you'd expect a reasonable shop to charge would also be helpful. I'd love to pull the sucker and take this on myself, but time is tight, and I'm enjoying rebuilding my chainsaw in my spare time instead smiling smiley

* fix the oil leaks (hopefully!)
* hardened valve seats (definite)
* more aggressive cam shaft (maybe)
* polish and port the head (maybe, with the prospect of K&N and richer needles at some point)
* lightened flywheel (convince me)
* any others ?

Cheers!
Curtis Walker

Curtis.. I see no need to pull the engine if you just need to rebuild the cylinder head. As for the rest it would depend on the running condition prior to the head gasket blowing. ie-how much oil was it burning-leaks from other places except the head and side plate areas.How was the clutch acting. Camshaft can be replaced with engine in place but be certain to install new cam followers along with the cam.
Everything depends on how much you want to do with the cash you can spend.
Sandy
conrad sanders

Curtis,

I don't think you have really given us enough info for us to have an opinion.

What are the factors that make you want to rebuild then engine? Why are you pulling the engine to do a head gasket and job on the head?

Where are the oil leaks? Unless the oil leak is the rear main, why would you pull the engine to fix oil leaks? Does the Positive Crankcase Ventilation (PCV) system work properly? Does it have a PCV system? What MGB engine do you have? What is the compression, and if it is low, is it being lost through the valves or the cylinders? Have you done a cylinder leakage test on it? Is the oil pressure low?

It will be easier to figure out what it needs if you do it with the engine still in the car and running. Once you disable it, the only way to figure out what it needs is to disassemble it.

Charley
C R Huff

Last night Top Gear had £10k to modify a used Renault Avantine to try and make it go round their track as fast as an Evo 10. It started off about 18 secs slower. They put bigger brakes on it - it lost a further 2 secs. They put sticky tyres on it - it gained 3 secs. They put it on a dyno and found it was losing nearly 50bhp from its original spec. They gave it a service including a new air-filter and intake (Clarkson said 'inlet manifold' but I bet it wasn't) and got most of that back, chucked out the original very heavy seats front and rear, but on the track only gained another 2 secs. In the end they said just how many millions were spent just in the UK on 'go faster' mods, and concluded that it was all a waste of time and money. I know Top Gear is 'entertainment' and their pronouncements must be taken with a large pinch of salt, but I've long held the same view. Personally no matter how much I spent and how much faster I made it go it would never be enough. I enjoy my MGs as they are, whether it be the 4-cylinder, 8-cylinder or 6-cylinder.
Paul Hunt

Curtis,

you did not mention the age/mls/Km of the engine.
Doing the head with the engine pulled, it is allways a good decision to install new bearings, new valve springs and a rebuilt rokker assy, oil pump and presure valve, water pump and thermostate.
A new timing chain would also be on my list and new rings, if pistons and bores are still O.K..
Then there is possibly a new clutch and a checked or even rebuilt dizzy, new jets and needles (needles depend upon cam and cr!)necessary to restore or increase power.
Be careful with selecting a new cam with followers. If the cr is kept stock, the results will be not that dramatic as quoted by some of the makers or dealers.

hope this helps

cheers

Ralph

Ralph

Hey Curtis,

When I rebuilt the engine in my B I just did simple, basic things. Trying to make the engine faster seemed a dangerous path to go down so I instead concentrated on making it smoother!

It was a US spec engine. All the emissions stuff was off already when I got it. I fitted new, HC pistons to it. Had the head skimmed and new valve seats fitted (actually did this twice since the first head had a crack I didn't find until later). I CCed the combustion chambers and evened the volumes out. I also cleaned it up a little and deburred it. Wouldn't call it a proper port and polish but it is certainly cleaner now. I had the whole engine balanced including the clutch. I just used the standard cam since that's meant to be fine for normal driving. I also fitted K&Ns and will look at changing the needles at some point. At the moment everything runs OK but will get it properly tuned when the car is complete. I also had everything else cleaned up and refurbished where possible. Dizzy, alternator, radiator, etc.

I found when I started looking at faster cams and so on it all starts getting expensive and I wasn't sure it was for much gain. But then I am trying to make a nice little car for driving about in, not something to race.

By the way I have a set of new K&Ns for sale if you need some. Can't remember the number off the top of my head but I think they are the ones that fit in the standard filter cans. I used the same ones with the standard back plate and a fancy cover plate.

Simon


Simon Jansen

Oh, when I say dangerous I mean in terms of things starts to cost an awful lot of money!
Simon Jansen

Thanks for your input, gents.

I'll try to clear up a few points arising out of your helpful posts:

As stated, the car is a daily driver, with no intention to be a race car, so reliability and ease of use are factors. Cost, if it's recommended, is not a problem, but silly money for bling or non-sensical performance gains is not the aim....it's just that I'd like to get what needs doing done so I don't have to redo the bottom end because of missed damage now. To this end, I'll be relying on the shop to provide advice as to how much damage is or has likely been done and therefore whether further strip down of the bottom end is justified. I certainly thought about just pulling the head myself, but noting that oil and water had mixed, I was leery about just doing the head when the guts may have been damaged. I'm relieved to read it's probably Ok to NOT have to pull the whole engine.

I'm not sure how many miles the engine has done since it was last refurbished, nor what was done at that time, but it has been a good, reliable motor to date, with good oil pressure - although it does require topping up a pint or so every few hundred miles - a combination of burning a little and leaking from where the oil hoses attach. I'm annoyed I didn't put my newly acquired compression tester to use on it prior to this event, and I didn't do so post-blown gasket either. So it's one of the things I'll have to be asking the shop about as I plan this.

My current thoughts, pre-shop discussion, and from what is written above, is to get the head P&P'd, the valves and valve seats done, the head and block checked for damage and skimmed as needed and put back together. No cam, flywheel, bearings or cylinder work (assuming these check out OK)....I agree that a well done head can be used later, costs less now, and will provide instant benefits.

The ancilliary's (distributor and carbs) are all in excellent knick and well tuned.

Cheers & keep 'em coming!
Curtis Walker

Oh, and thanks for the K&N info, Simon - I'll give it some thought and get in touch if the bank manager lets me after this is all done....it's one path I've been interested in for few horse gain, but on the understanding it's only useful with a P&P head.

the engine is an 18V, no anti-smog gear, I believe from memory it's the correct spec for my 1971 BGT, but haven't confirmed if this is so using the relevant tables!
Curtis Walker

Curtis,

If your blown head gasket is only mixing the oil and water, by which I mean a combustion chamber has not been breached, then a compression test will still be valid.

As for the likelihood of damage caused by coolant in the oil, it depends upon how much and how long you drove it that way. I have had engines mix their fluids, corrected the problem, and had no other trouble as a result of the failure.

Once the head is off, the cylinders can be assessed. If their condition suggests that rest of the engine needs to be torn down, then I suspect it would be false economy not to do it all. This is especially so when you are paying someone else to do the work. At the very least, it will get rings, rod bearings, main bearings, checking the rods, timing chain, probably an oil pump, having the flywheel resurfaced, and a new clutch. I would not spend money on a lightened flywheel when the purpose is a comfortable daily driver.

Your oil use seems pretty serious unless it is mostly leaking, and leaking that much oil would make quite a mess. Perhaps it is just going through the valve guides, but if you are tearing the engine down, I would give serious consideration to reboring and new pistons.

If your engine is a low compression model and the pistons are going to be replaced, I would consider turning it into a high compression model. If it is still a 71 engine, it should not be an 18V, but if it is, I would suggest considering a duplex timing chain upgrade.

As for the head, I would weigh the cost of having yours done vs. exchanging it with one of the well-known head modifiers/builders. Peter Burgess comes to mind. It may not cost much more to put a nice custom head on it than to have yours done in stock configuration.

The cam is a bit of a personal choice, but a mild bump up for a road going engine should be considered, particularly if yours is worn. Be sure to replace the cam followers if the cam is replaced. If you do the custom cam, be sure that the installer knows how to time it properly or it will be money wasted.

Still, I suggest doing as much assessment as possible before removing the head because there are things that can’t be easily assessed after it is removed. It is entirely possible that all you need to do is the head.

Best of luck,
Charley
C R Huff

The local head reconditioner guy has the head in the tank at present. He says things don't look too bad - and it sounds like the bottom end was spared major damage - I guess I drove less than 10 miles on it post-gasket blowing. Gonna check the pistons and rings for wear and tear and possible replacement - apparently the compression in the better cylinders was about 150-160 PSI.

I've decided to go for a valve grind and port polish and flowing, along with hardened valve seats - so a somewhat minimalist approach I guess, but it should be a nice upgrade and provide good future proofing until / when the bottom end needs redoing.

The cost of shipping a pre-done head from overseas is prohibitive - esepcially as it would require me to ship my head back as an exchange unit, but thanks for the suggestion - and thanks for the suggestions to date - most helpful!!
Curtis Walker

Curtis,

I forgot that you are in New Zealand when I suggested swapping heads.

I'm a little confused about your intended inspection and future plans. If you are inspecting the rings, aren't you already into the bottom end?

Except for roadside repairs, I don't inspect/reuse rings, I just replace them. Then, since they are out anyway, I would typically replace the rod bearings.

Then consider that you should run a glaze breaker through the cylinders before installing the pistons and new rings. It can be tough to keep/get the grit from glaze breaking out of the engine, so you would typically have the engine out of the car and the crankshaft out of the engine to do this. Then since the crank is out, might as well put in the main bearings, and as long as you are in that deep, might as well rebuild the rest of it.

I think this job is likely to snowball on you. Not that there is anything wrong with that. I've certainly done my time in such blizzards.

Charley
C R Huff

Curtis,

I too am shopping for head porting work and three-angle valve job. I've always been advised to decide on bore and piston size, CR, and level of head modification, before choosing a cam. Also consider how you want to drive the car. If you do most of your driving between 2500 and 4000 rpm, you do not want a cam that sacrifices this rpm range while coming on strong at 6000. For road use, a lot of specialists have told me that the factory cam "is not a bad cam".

If you're doing even mild performance upgrades: "fast road" head and cam, 9:1 pistons, .060 overbore, etc, and you don't know the condition of your engine, I suggest you rebuild the whole engine. Use a good machine shop that you trust to check/regrind the crank bearing surfaces, align-bore it, de-ovalize conrod bearing journals, check and rebore cylinders, balance the whole thing. I haven't heard any persuasive arguments for lightening the flywheel in a road-going engine, but check the condition of your ring gear. While you're at it, replace your clutch and at least your front transmission oil seal. If there are any other issues with your transmission, this is the time to resolve them. Do you have overdrive? If not, would you like it?

If your lower end and cylinder bores are good, you might want to consider keeping your CR down, leaving the engine in, and going for the Moss supercharger. That has always seemed really expensive to me, but compared to all the foregoing, it might not be such a bad alternative. And since it is bolt-on performance, it can be unbolted and put on a different car.

FWIW,
Allen


Allen Bachelder

Lightening the flywheel is something I wish I had considered when I had mine rebuilt. I was wondering if it makes the car a little faster to rev or not. For the last few years I've been teaching myself to heel toe in my every day car just so I can have some fun in the B when she's done. I always wondered if a lightened flywheel made it easier to blip the throttle?

If you've got everything out of the engine definitely get it balanced I would think.

Simon

Simon Jansen

The head is at a head specialist, while the block is still in the car at a regular garage.

As written above, I don't think I'll get to the bottom end this time - so no cam job (happy with the street cam), bearings, cylinder or ring work - although I'll get on the phone to the shop again tomorrow to confirm the cylinders, rings and pistons in particular don't need any work.

My longer term (i.e. 10 year) plan is a full rebuild and balance at some stage to allow a supercharger - but don't tell my fiancée that just yet! I suppose when I get that far in, I could play with a new flywheel etc.

In the meantime, a nicely redone head ought to do unless pushed.
Curtis Walker

Curtis,

A head that breaths well is the biggest single performance improvement you can make anyway.

FWIW,
Allen
Allen Bachelder

Curtis,

if you only do the head, do not have it skimmed to increas the CR, otherwise you might run into problems with the (old) bearings.

As Allan allready stated, the head can be modified with amazing results! A good 3 angle valve job, new springs and a clean up of the runners are allways worth the money spent.

For further plans, i would try to pick a late 1971 to 1973 engine and Peter Burgees book upon powertuning the MGB 1800 engine. This engine is the most potential one for a powertune rebuilt, as it has the most interesting head fitted and is equiped with the lightest crank ever used on B-series engines. Mine is a modified 1972 with 1868 ccr and all the 'friendly' parts from differnt sources. It acctually was checked on a rolling road producing 122 rwhp at the wheels, running flat top pistons, lightened conrods, crank and fly, HIF 6 carbs, racing dizzy, double row cam gear and piper 285/2 cam.
Building this engine took some time but this is not an issue, if i got you right?

Ralph
Ralph

Curtis-
I agree with Allen. A good flow job on the head should be considered to be a precursor to any consideration of a different camshaft. If done properly (such as in the case of a Peter Burgess Fast Road head that gives 25% more midrange torque and 30% more top-end horsepower), the increase in power output can be such that you'll be satisfied with the results and forget about changing the camshaft, which means lots of fun experimenting with changing the needles, and more fun changing the ignition curve as well. Cheaper in the end, too.
Steve S.

If you ever thought of uprating the oil pressure relief spring...
now the time to do it! It's an AWFUL job to perform while the
engine is in situ.
Daniel Wong

Ralph,

Do you know the number/letter designation for the engines you are talking about? I've got two 1971 engines (at least that is what I think), but maybe they are the early 71s. They are both 18GK, and they don't have the big intake valves, though I suppose the heads could have been changed before I got them.

Charley
C R Huff

Curtis, what were you going to do on the exhaust side of things? I keep wondering if I should invest in a better exhaust for mine.

Simon
Simon Jansen

Simon,

Unless you're really going to the limit, the stock MGB exhaust manifold (pre-Zenith-Stromberg) is very hard to beat. I've heard a lot of folks advise to stick to the stock manifold, and either remove the front muffler or go Peco from manifold on out.

Daniel,

Point well-taken. This from a guy who's been there and done that. IMHO, all MGB engines ought to have the uprated spring. Why can't one of us invent a tool for changing one of these springs in situ?

Steve,

That's the shortest "Steve S." post I've ever seen! Or did you just accidentally push the "Submit" button prematurely? ' Hope you are well! 8^)

Allen



Allen Bachelder

In all honesty, I should admit that most of the "advice" I refer to comes from Steve S. So, when he says "I agree with Allen." he's really giving me credit for what he said in the first place.

Very kind, Steve,

Allen
Allen Bachelder

"Unless you're really going to the limit, the stock MGB exhaust manifold (pre-Zenith-Stromberg) is very hard to beat. I've heard a lot of folks advise to stick to the stock manifold, and either remove the front muffler"

Yep, done that :) Removed the front muffler I mean. Better ground clearance (handy since I am lowering the car) and a much nicer noise out the back! Guess I will stick with the stock manifold for now.

Thanks!

Simon


Simon Jansen

The car actually came with a pico muffler (I think - it's not hear to check) - and IIRC the front muffler has been removed already, but the manifold, as far as I know, is stock. So it looks as though the head will be getting a nice exhaust to go with it!

I'm off to the head reco. shop tomorrow, so will provide an update tomorrow!
Curtis Walker

Curtis,

I'm curious as to how the garage can tell whether there is any damage, or indeed wear, to the bottom end without taking it apart?

As for power-tuning, well on the one hand, a standard MGB is not exactly a rocket ship. On the other hand, it would be easy to spend the fat end of £2k on the engine (£500 on the head, £200 cam, £300 carbs - much more for a Weber, £100 for a balance, £100 on a distributor to match, plus whatever it costs to update/upgrade clutch, lubrication, cooling) and get a car that goes much better but is temperamental and drinks fuel like it is going out of fashion. It's your choice. Mine was for the latter by the way, but I don't drive it every day.

FWIW

Neil
Neil

charley.
i have just bought an engine to rebuild for my gt. it is a 71-72 with the big valve head. i think the numbers you are looking for are 18v 581 or 582.
bob
1970 bgt.
Bob Taylor

Thanks Bob,

I was looking in the Haynes the other day and it seemed that the GK was the last one before the V series. After that there were quite a pile of numbers to look through. I appreciate the help. I'm not really in the market, but I'll keep my eye out for a good deal.

Charley
C R Huff

Neil - good point, and I don't think they can, whichis why, as I understand it, some garages absolutely won't guarantee a head gasket fix without breaking down the bottom end. Garage guy was gonna run feeler gauges and inspect the rings and cylinders, but wasn't offering to look deeper, and I'm not pushing for it either.

At this stage I'm happy to get a good return on investment by getting the headwork done, rather than spending lots on - as you write - incrementally less gains for more temperamentality - particularly for a daily driver.
Curtis Walker

At this point in time, I would concentrate on getting the head sorted ie. a valve job, hardened exhaust valve seats, resurfacing and crack checking. The other major point is to check that the block is true and if not have it decked. Performance options can be added later as your budjet allows. RAY
RAY

"A head that breathes well is the biggest single performance improvement you can make anyway."

Upgrading to a V8 or V6 tops that easily. ;)
Carl Floyd

This thread was discussed between 17/11/2008 and 25/11/2008

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