The MGA With An Attitude
BROKEN ENGINE Considerations - BE-101

At 12:03 PM 11/16/04 -0700, John Clark wrote:
>".... My engine is a 1489cc ... with a broken con rod ... and hopefully salvageable crank. What should I do?"

First order of business would be to disassemble the engine to see what it needs. These things are pretty robust and hard to kill. They can often toss a con-rod and/or break a piston with not much other damage. If the crankshaft is damaged (but crack free), it may be economically practical to have a single bearing journal welded up to rebuild the material, then regrind it. If it needs more than one journal repaired, then you should probably look for another crankshaft. If one cylinder needs to be sleeved, and the crankshaft needs to be welded, then you might look for another engine (good time to get a 1600).

These days 1500 blocks are almost free if you pay shipping charges. 1600 blocks are worth about $100 USD (in 2004) for a bare block, which may be the way to go if you need a complete engine overhaul. The only significant difference between 1500 and 1600 is the cylinder block and pistons (which you may be buying new anyway). Everything else is interchangeable. Both engines use the "15" cylinder head and the same crankshaft.

At 02:03 PM 11/19/04 -0500, John Clark wrote:
>".... Is a new cam worth the $$ over a used one?"

Probably yes, unless you're very lucky, and you really understand what you're looking at. Used cams are commonly somewhat worn in MG engines. See cam and tappet operation and cam wear.

>"How bout the head?"

Valve guides are usually worn and in need of replacement. It is common (but not gosple) that valve seats suffer recession (especially exhaust valves) so you may need machining for valve seat inserts. If it needs new seats, by all means be sure it gets hardened steel seats, which is the prime ingredient for a no-lead fuel engine.

>"Should I replace valves with the stellite type,"

Please read about stellite exhaust valves. I happen to like stellite exhaust valves a lot, but that's because I commonly work the engine hard. If you drive casually, and you don't expect to put more than another 50,000 miles on the car, then they might be a waste of money.

>"springs, rockers, push rods...etc?"

Stock springs might last indefinitely with a stock cam. I have never known anyone to break a valve spring with the stock set up (but I'm sure it has happened). If valves and seats suffer a little valve recession, but not enough to need new seats, it may be appropriate to shim the springs slightly to return original rest height. There may be reason for switching valve springs for certain performance mods.

Please read about rebushing rocker arms. The rocker shaft is commonly worn on the bottom at the bushing journals, and usually needs replacement. Rocker bushings may last twice as long as the shaft, and might not need replacing. For an engine expected to run lots of miles in the extended future, you might consider a new rocker shaft with hardened surface, but those are quite expensive and may not be cost effective.

Pushrods may last forever, unless you smash a valve (not so rare) and bend a pushrod (more rare). There may be other reasons for changing pushrods with certain performance mods.

Tappets have to be replaced anytime you install a new camshaft. See cam and tappet operation and cam wear. If tappets are a little worn, but the original cam is in generally good condition, then new tappets may prolong the life of the cam. If you intend to use the original tappets on the original camshaft, be sure you do not mix them up. Switching tappets around greatly accellerates wear on the cam lobes. There may be other reasons for changing tappets for certain performance mods.

>"I want this car to be worth the maximum $$ without going overboard on the engine."

Ah, the holy grail! Good luck with that. The trick there is to do value analisys before spending money on "upgrades". Many (most) performance modifications cost more than could ever be expected in increased market value. Some performance mods can shorten the life of the engine, so might actually reduce the value of the car. The better money is spent on things which will improve the durabulity of the engine, especially if you intend to drive it a lot. If you ever get the notion that time and money you spend will be returned in sale of the car, you better have the buyer on the hook with cash in hand before you do it. See economics of restoration.

>"I really want to drive it 5-10k miles a year."

For how many years? I mean, how many total lifetime miles would you expect to put on the new engine? If you drive casually, and you don't expect to drive it more than another 50.000 miles, then it may not merit anything special. The concern is for driving LOTS of miles, like enough to wear out the whole engine, or for abnormally hard driving.

>"Should I even consider the 1800 MGB engine? "

Lots of people do that for MGA these days. NAMGAR has even created a special judging class for the MGA 1800. See think about it. When NOT considering it for concours show, 90% of the prospective buyers might actually appreciate the 1800 engine, and it should not affect the market value much in either direction (at least in North America). None of these options will increase the value appreciably, so you would be spending the money strictly for your own pleasure.

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