M/T Series Engines

History

As noted on this page, the O Series started as an 8 valve SOHC with a later modification to a cross-flow, 8 valve SOHC head.  However, the 8 valve had limitations and so a natural progression was to a 16 valve DOHC engine using the same O Series block.  The M16 as it became known was fitted to the Rover 820 from its launch and also to some 220/420 models up until 1991/1992.  Modifications were then made to the M16 and it then became known as the T16, again seeing service in the 200/400/600 and 800 range, with 140bhp in EFI form, and up to 200bhp in the turbo form as fitted to the 800 Vitesse, 620 Ti and Rover 220 Tomcat coupe.

Why go this route of a 4 pot, twin cam based on the B Series when everyone is doing the V8?

In short, there are a number of reasons for why a few of us have chosen this route in either n/asp or turbo form.

• It can be fitted directly to the existing gearbox immediately making for a less complex and costly installation.
• The engine weighs a little less than a B Series but not as light the K Series so handling should remain the same.
• A good, strong engine with plenty of torque across a wide rev range.
• Minimal, in fact probably no body modifications necessary.
• Good fuel economy, reputedly, Roger Parker reckoned on 50mpg or more with ECU/EFI at cruising speeds.
• It is a logical progression of where the O Series would have gone.

Roger Parker notes:

"The main difference from the earlier O series was a new head casting to enable this tall engine to fit under the bonnet of the XW series 200/400 ranges comfortably, as early 220 and 420 models had to have a bump in the bonnet for clearance. The other main change was the way ancillaries were grouped and hung from the engine, now being a much simpler arrangement in a cluster off the front of the engine when in FWD form.

O2, M and T makes a very good conversion for the MGB, as it should from the historical perspective of O series originally being designed for the B. It is simpler to fit in some areas than a V8, such as fewer body changes and no need to change rear axles. IT is far more difficult than a V8 in detail areas such as fuel and ignition systems, wiring, manifolding and small items. With everything available off the shelf for V8 conversions once the body mods are done it can then become almost a bolt in conversion. The opposite is true of the OMT conversions.

Once on the road though with full standard engine management systems you reap the reward of what is an efficient engine in 16v form, with a very useful drop in vehicle weight to pull. This is confirmed by fuel consumption figures in the mid 30's for normal poddling around and an easy to crack 40mpg on a run. On much longer runs where steady speeds of around 65mph to 70mph are held 50mpg has been cracked on several occasions, and this is not due to a fast running odometer.

I have seen similar results on about 20 other cars that have used these 16v engines, but of note is the fact that the Lucas Hot Wire management systems have a clear advantage over early MEMS systems."

I've had experience of the T16 in my 1998 Rover 420, and it is good for 140bhp at least in original format in the Rover saloons, I believe, as used in the Rover 420/620/820.  The downside is these are older units, the youngest being 1998/99, so it is likely there will be more miles on these, and parts maybe a little more difficult in the future. Fuel economy will not be as good as the K series, and these are heavier than the K Series.  The choice of gearboxes for these engines is very limited and hence the favoured route is now to the K series for its lower weight and better power output opportunities. That said, people are now virtually giving the cars away so a useable engine will be easily sourced.

Thanks to a good contact on the Brit-Cars Forums who goes by the name of 620Turbo, for obvious reasons, a new section is added below with a bit more history and a summary of the technical differences and answering some of my queries:

Q -At approximately what age  did the engines get a change in ignition and engine management?

A - The dizzy was removed and replaced with a wasted spark ignition system, along with an updated MEMS sometime in 1996. It may have coincided with the mildly revised 800. (Note - the distributor sticks out from the back of the head and would foul the heater box - see fitting an O2 Series engine)

Think this change also means a different flywheel as the number of teeth is different. Therefore, engines and management could be interchanged if you swapped the flywheel . . . and cams obviously because the wasted spark cam does not have the rotor drive on the end of the exhaust cam for the ignition.

Q - My 1998 Rover 420 had to have a new engine at 8 000miles as it was consuming so much oil, and others talked about sticky valves - yet the engine always seemed a solid unit - are there any issues of which one should be aware?

A - They are a very strong unit, old tech, but good nonetheless. They are long stroke which shows their long-in-the-tooth roots, but this means you get lovely, low speed pulling power and mid range performance. They do suffer poor fuel consumption unless motorway cruising, where the engine will be sitting in it's torque band, and poor emissions comparatively speaking.

Hence nobody makes long stroke petrol engines like this and the death of the T series. . . . inefficiency.  (Note - This why the K Series was stretched to 1600cc and 1800cc to offer a lighter, more efficient engine to replace the T Series)

Apparently the actual guts of a T series, meaning the pistons and rods are not as nice as that in the preceding M series, which I can believe as the M series was a little smoother. (Note - The B series also benefits in terms of refinement from balancing, so balancing would make sense here, too, if rebuilding.)

The early engines, (1992 and 1993 build) suffered from problems with sticking valves when the engine was cold. This would get so bad that they would also do it when warm. It mainly affected cars that did short journeys and was due to the valve guides being too tight together with carbonisation around the valve shaft where it passed into the tight guide.

A lot of cars were retro fitted with carbon break valves, which seemed to cure the problem mostly, but the factory line fix of fitting brake valves AND different valve guides was done sometime 1994/1995.

This can be a problem as the unburnt fuel from the misfiring pot can result in bore wash.

1996 revisions to the engine, the new management, wasted spark, etc also meant a revised head gasket, comprising of a Klinger multi layer steel (MLS) head gasket AND improved tolerances for head and block face.

Previous engines did not have the MLS gasket and did the usual T series and M series and O series, weep from the cylinder head/block join around the cylinder number 4 corner, at the front. You will see it immediately, sometimes it is just a little damp corner with some dried oil indicating hardly anything, other times it is gushing out.

Engines can be retro fitted with the newer head gasket but the oil restrictor in the block needs to be removed, which can usually be done with a screw and a pair of mole grips. Cleanliness is paramount and every minute spent in preparation of the head and block surface is vital and they should be perfect for the best end result and no more oil leak.

Cam covers always leak oil, and need cleaning up and new seals. It's easy to strip cam carrier bolts when putting cam carrier back because the T series uses 8 or so large bolts, which when you are doing the carrier up have to depress the cam, so these bolts need doing up in sequence, very progressively.

Exhaust manifold usually a problem. If it has been off, it will likely not have been put back properly and could have well pulled the threads in the head. Key here is to get a new gasket, goods studs and nuts. Clean everything up, then put blue threadlock on the end of the threads and screw the nut on so the nut is at the end of the thread. Wait for threadlock to go "off" then slowly screw in each stud using the "glued" nut.

This should mean the studs go much further into the head as the usual problem is the studs only go in a few turns, then the nut goes down the shaft so the time you torque it, it pulls the stud out as it does not have enough thread on it in the head if that makes sense.

Sump gaskets are easily dealt with. Basically, most things can be sorted.

Something to remember is that heads are the weak point when the engine overheats. If the engine has been overheated, usually as a result of lack of maintenance on cooling system or other neglect, when the head gets really hot, the valve seats usually move in relation to the valve guides. You then end up with a nasty misfire and lack of compression because the valves are not effectively closing.

Scrap head in this case.  

And to avoid overheating on some units, the engines with A/C and the thermostat in the top hose need new thermostats every 40K miles. Symptom is temperature dropping from normal operating temperature slightly when off gas going down hill.  You could leave it, but it's not good for large metal objects to be expanding and contracting the whole time, even slightly. That's one of the reasons why the 4 pot K series blow head gaskets all the time. Head and block always expand at different rates and the head gasket is the thing stuck in the middle.

This is the best Rover engine made for years. If maintained properly it will do a lot of mileage. It has its annoyances, like the leaking cam cover seals, etc but these are easy to sort.

Later engines are better in my opinion as the tolerances were generally improved. I'm not sure if this was a result of any BMW influence anywhere or not.

Q- many are considering the turbo version and these appear on Ebay regularly, what is your view on them?

A- My 620ti did 130K miles and was still going strong when I saw it sell on e-bay recently by the guy I sold it to. Run on Mobil1 by me since 60K and loved and looked after by previous owner from new. It did not burn a drop of oil when I sold it and still on standard turbo. Not a tick, rattle or anything and still ran 100% compression as verified by 165BHP at wheels on rolling road and lovely smooth power curve.

All this applies to turbos as well as n/a. The main problem with the turbos tuning IMO is not the pistons, etc, although they are weak it is the small turbo and crude intercooler.

On a hot day, blasting around, on standard boost the charge temps become scary. The turbo was only rated to 180PS by Allied Signal/Garrett who made the thing and the same turbo was used on 1600cc 8v Fiesta RS.

Therefore, good power and tuning can be had on standard pistons and rods, provided the intake temps are looked at and a larger turbo is one of the first upgrades.

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