TD engine rebuilt - play by play


With hearty thanks to the author, Andy Moyce


In the following story Andy describes the ups and downs of an engine rebuilt of his 1952 MG TD. A lot of the technical part was done by John Davis, one of the restorers of the MG TD featured in this homepage. The restauration story will be delivered in several parts (simply because I want to translate it for the german mirror of my site, too). So lets sit back and listen what happens...


Part One - The story begins

Date: 10 November 1997

The background: 52 TD last registered in 74. Spent the last three years in a frame-off restoration. Left the engine in the car with the plan to drive it for a season or two before starting an engine rebuild.

After less than 1000 miles the engine started making noises which forced my hand.

The engine is painted gold and the numbers don't match. Both the car and engine are in the 120000s.

The valve cover is chrome with a plate that specifies .012 for valve settings, prompting speculation that the camshaft has been upgraded.

Step 1. Decision.

The noises started when my copilot and mother of my children and I were cruising at about 55. The past few weeks of driving have given me the opportunity to put some substance into my promises that this car is for both of us. After three years of lost weekends the car finally started to assume its role of catalyst for our spending time together as the nest empties (kids now in high school.) We were just starting to feel invincible and talking about long weekend (and more) trips to exotic destinations when the noise conjured up visions of roadside stops waiting for the tow truck, etc.

We agreed that a) the car is a worthwhile investment and, b) a rebuild to improve reliability is necessary. The budget was mentioned- -I'm planning $4000 and hoping that it will be considerably less- - and approved (a major step) along with tacit approval for my weekends disappearing back into the garage.

Step 2. Assemble the team.

My faithful friend Paul is enthusiastic. He is a former Lotus owner who likes to work on other peoples' cars. He was there for about 80% of the restoration and looks forward to exploring the mysteries of the XPAG engine.

Through the advice of other local club (Sorry Safari Touring Society) members I called John Davis. John is currently between TDs, but has rebuilt his own and club members engines. On his recommendation I called the machine shop in San Leandro (20 miles away)and spoke to Darryl Aitkin. He has machined many an XPAG and John recommends him highly.

I have spoken to Skip Kelsey in general terms about this and will be in touch with him this week to let him know that we are under way.

A timetable was agreed upon with this weekend for removing body parts for access, next weekend for removal and disassembly. Darryl said that he would like the engine by mid November so he can have it done and out of his shop before he closes for Christmas vacation.

Step 3. Wrenches and buckets.

Paul and I started removing parts yesterday, following the cryptic instructions in the service manual. We actually got most of it done in half a day.

Though the photos show the headlamp brackets left in place we decided to remove them, even though this meant unwiring the headlamps and pulling the wires back. Reasons - - the brackets look too fragile waiting for the heavy engine to bump them during removal and I didn't want to ruin the paintwork unscrewing the large nuts that hold the brackets to the radiator bracket.

I saved most of the antifreeze/water mixture in a gallon bottle. How am I supposed to dispose of the rest? Removed the starter, since they said to. It looks like it could have stayed until the engine is out adn I wonder if that is a RHD leftover. Took the manifold off since it was pretty accessable. So far haven't been able to reach the engine grounding strap to remove it.

Took the transmission cowl off, having to strip off the insulation I had placed under the carpets. The manual says to remove the gearbox cover and replace with cardboard to protect the innards of the transmission. The gearbox cover shouldn't have anything to do with engine removal and we wonder if they mean to remove the remote control mechanism. The photo labeled "ready to remove'" or similar shows both the remote and the cover still in place. Removed the four bolts holding the remote in place but the assembly wouln't lift off. There is a warning in the manual that if you do the wrong thing all of the syncromesh balls will fall to the bottom of the case, so we backed out. Will seek John's advice on that one.

I whined a lot about being told to remove the floorboards, mostly because of the difficulty I had mounting the seatbelt anchors through them into the chassis. The day got late and we were tired, so I'll do that next week. Nuts and bolts are either being placed back on the appropriate part or stored in plastic bags. I finally found a marking pen that will write indelibly on plastic bags.

All in all a good day, with no major mishaps . . . no broken bolts and no scratched paintwork. This week I need to find and rent an engine hoist. Next Saturday John arrives with his engine dolly and we pull that sucker.

Part two - Engine pulled and disassembled

(To Part One)

Date: 18 November 1997

I wrote all of this yesterday and thought I had posted it but I must have pressed the wrong button on the computer. Good thing English cars are more reliable than Computers. If someone finds this same story posted elsewhere I apologize.

Saturday was engine pull and disassembly day. It started out dark and rainy, as if to underscore that the season is for repairs, not for driving.

First minor crisis was getting the engine hoist into the family car. I rented one for $24 a day at the local equipment rental. It's a sizeable machine which comes apart into metal beams, the longest of which is 6 feet.

They supplied it only with a chain on the beam to be held together with a large bolt, which was not supplied.

Fortunately John brought a large rope with him and I found a large bolt and nut in my spare parts department. John also brought an engine dolly, which made the disassembly process much more pleasant.

I finally succumbed and removed the floor boards after discovering that there was no other way to release the rear engine (actually transmission) mount. The rails on either side of the driveshaft tunnel (under the handbrake) have to be moved to the side to release the motor mount, and the floorboards are in the way. The big deal about the floorboards for me was the trouble I went through to get the seatbelt mounts to go through the chassis members. Access to the anchor nuts was worse than typical English design, but if I got em there once, I can do it again.

I managed to remove the remote from the transmission with some levering and rotation. After it was off I found that mine is a later model which has a removable housing that holds the rear of the first and second gear shift rod. It is meant to be removed first, and I hope I didn't bend anything.

Some of the mystery of transmission was enlightended. There was discussion about redrilling and adding bushings to the remote housing, and apparently that was done to mine in an earlier life. The problem was that the nylon bushing meant to fit in the front bore was stuck on the remote shaft just behind the bore. With some grease and careful tapping with an open wrench I was able to get the bushing back in the bore. I think I'll tap for a small set screw to keep it from coming out again. The rear bore seems to have some sort of bushing in it, though the top of same has the spring and plunger which push right against the shaft. I imagine that the rattle will be much reduced by positioning the nylon bushing, but I'm a long way from a test drive at this point.

Anyway, once the motormount was off and the drive shaft lowered the engine lifted easily on the hoist. Had to do a little bit of rocking to get the u-joint flange to clear the chassis cross member, but then we pushed the car backwards after hoisting as high as the garage ceiling would allow. We then lowered the unit to the floor to remove the bell housing bolts and transmission, then hoisted into position on the dolly.

The noise and its cause(s).

After removing the head, we could see the top of the number one piston was pitted. There was a crescent shaped path across the top, two inches at its widest, which resembled that nugget gold jewelry that heavyset men like to wear in bracelets and watchbands. This was mostly near the perimeter of the piston head. There was an indent at the edge, about 1/4 by 1/2 inch that communicated with the seat for the upper ring. The ring was fractured into several pieces. The other pistons had a few fractured rings and some minor pitting, but were overall intact. The head and the valves were pretty unremarkable, as was the lower end of the pistons and crank.

There was some scoring of the big end (rod) bearings, mostly circumferential lines in the center of the bearings. These bearings are only 1000 miles old.

The main bearings were rubbed to a dull grey parts. The timing chain was stretched so there was about a half inch of lateral play on the side opposite the tensioner. The tensioner itself was in good shape. The camshaft was a little reluctant to be withdrawn, but otherwise looks pretty good. The bearings are somewhat worn but no obvious grooves or fractures. The lobes all look finely polished. The cylinder bores also look okay to the naked eye.

The oil pump gears turn freely and look symmetrical. I tried hanging the crank from the driveshaft flange and tapping with a hammer (Bill Phy told us that this is how the old mechanics tested for cracks.) It chimed nicely with a different pitch at each lobe (watch for a PDQ Bach symphony for crankshaft and orchestra) and there was some clanging overtone, which may have been from the wire hanger or could be the dreaded crack. Obviously more sophisticated tests are pending.

Part three - Trip to the machine shop

[To Part One][To Part Two]

Date: 22 November 1997

I took the engine in parts to Darryl at the machine shop . . . Miller and Hodge in San Leandro, CA. Highly recommended by our local MG gurus.

He first ground some of the grit off of one of the pistons and found that it was 80 oversize. He spent a few months at Automotive Engineering early in his career and said that it was common for them to bore all blocks to near maximum so they only had to stock one size of piston and set the machinery up once for multiple engines.

We didn't know if we would have to sleeve the block until a call to Skip Kelsey (Shadetree Motors) verified that pistons are available in 100 and even 120 over. Before we knew that there was some interesting discussion about sleeves and pistons. He said he has a couple of XPAG engines that he is fitting with 1500 cc sleeves. Sometimes the bore actually gets into the water channels, but he says that as long as he has metal above and below, the sleeve can handle the load.

We talked of lightening the flywheel, which he says makes a big difference in acceleration. He said that in racing engines they have had some problems with crank failure that they attribute to torque from the driveshaft during deceleration, presumably worse without the flywheel weight to even out the force. He will balance the crank and flywheel. I had thought that this balancing would eliminate some of the need for a heavy flywheel, but he said that the engines were balanced at the factory and the original engineers had some reason for specifying flywheel weight. I still haven't decided what to do on that one.

He checked the crank for size and it is standard. He still needs to magnaflux, but said that most of the failed driveshafts he has seen were severely machined before they cracked. I won't know the answer to that one until Monday.

His theory for the piston failure is ignition of the oil that gets around failing rings. With the gas mixture igniting you don't need the pressures that deisel engines produce for oil combustion, and the added heat could have consumed the edge of the piston.

He showed me how he will modify the head, replacing the valves with larger ones, and adding seats for the exhaust valves. He'll enlarge the intake ports to the size of the gasket openings and make sure they are of uniform size.

Line honing of the main journals will be done only if needed. It tends to weaken the engine and can be assessed before removing any metal.

He'll work on the oil pump and confirmed what I had previously learned that it takes a lot of machine time to get the gear clearances correct. We won't upgrade the rear oil seal, as John thinks that the standard seal is better if installed correctly.

So, next step is the cleaning and magnafluxing which should be finished by Monday. Then we will talk and he'll give me a detailed estimate of time and materials for the job.

The options I will need to decide involve extra work on the head and the flywheel. I think the honing and balancing are pretty much standard.

All in all it was an entertaining and educational trip. I appreciated the time he spent showing me what's involved in the job. We haven't yet gone into detail on how much re assembly he will want to do and how much we can do with John's guidance. Some of that will depend on John's availability, so the completion date for the machining will be a significant factor.

We're moving along . . . stay tuned!

Part four - Crank is okay

[To Part One][To Part Two][To Part Three]

Date: 25 November 1997

Just got off the phone to Darryl, the machinist. My crank and head passed the magnaflux with no problems. He put together a bid for all that we have discussed, which comes to $2000 plus change.

Parts aren't included in this, as they will be supplied directly from Skip Kelsey and billed directly. There will be additional oil pump work, which isn't in the estimate. He won't know what's needed until he starts working on it on the clean block.

He'll start next week and should be finished in about ten working days.

I will pick it up in roughly the parts condition that I delivered it in, and it will be up to me and John (mostly John) to put it back together. John's considerable experience makes this plan work . . . I would not tackle this on my own (I would ask for the short block to be assembled at the shop.) The estimate is pretty detailed . . . I'll quote only some of what look to me like wise options to improve performance.

I haven't added up all the expected parts but that will probably run an additional $1000.

If my parts estimate isn't too far off, and if the oil pump machining doesn't go way over, I should be within budget.

Darryl told me there is no worry in boring the block to over .100 or even +.120, so in the end I expect to have a fast and reliable engine, ready for years and years of happy motoring. I may even have money left in the bank to raise my rear end ratio from the current 5.25.

Part five - Back from the machine shop

[To Part One][To Part Two][To Part Three][To Part Four]

Date: 13 December 1997

I picked up the engine yesterday. The total for machining was $2300. The parts bill included only the valve seats and stem seals. The rest of the parts will be billed directly to me by Skip Kelsey at Shadetree. . . I'll pass those figures along when I get them.

It is certainly a lot prettier unit than what I brought in there. The sump and block look like new aluminum. Darryl told me that after degreasing and bead blasting he changes to new beads and reblasts at lower pressure, which gives this finish. He tells customers to finish with some clear enamel, though of course we MG purists insist on painting with the red paint.

He has the new camshaft and oil pump installed as he machined the oil pump on the block. The crank is hand tightened only and the new bearings are in.

The rods are installed and balanced on the new pistons and the rod bearings are installed finger tight. I have new nuts (non-castellated) for when we torque the rod bearings. The rocker arm has a new shaft and he machined a couple of the arms so they seat properly on the valve stems.

He showed me where we'll have to trim the manifold gasket along the top of the intake ports to match the machined port. He gave me some detailed explanations of how he ports the head, taking into consideration laminar flow characteristics, which dictate a smooth port with no sudden widening or narrowing.

He ended up lightening the flywheel from 25 down to 17lb., which is a more than I had expected. He told me of his race engine experience in which they drastically lightened a 350 horsepower engine (lighter flywheel and crank, titanium rods, etc.) and were disappointed to see only a couple more horsepower on the dynamometer. When they drove it, though, the driver told them that he had to modify his techinque in accelerating out of corners because acceleration was so much quicker, and this was reflected in his race performance.

I take comments that I won't be beating newer cars off the block, nor do I want to, but hope that this will show up in performance, especially when I raise the rear end ratio. The cost of the lightening was $240 for four hours work. With time that will fade into memory as a small part of the rebuild budget.

The whole engine has been balanced and the horizontal bore for the main bearings was checked. The pistons have been balanced and machined to reflect the compression change. It looks like the extra head work (match port, match cc comb chambers, resurfacing on the invoice) came to a little over $300 of shop time.

The crank needed very little work, and all of the jounals are correct and standard. Discussion with other MG people yielded the opinion that my crank (a 16000 series) was a replacement and a type that almost never fail.

The oil pump needed some work to get the shaft of the driven gear to line up with the hole in the pump. It was off enough that it had caused wear on the old shaft.

He also told me that he found some of the blue silicone gasket sealer lodged in the pressure relief valve of the oil pump - the one that opens when the filter is clogged - and that was probably reducing oil flow by 60% or more.

He likes to use sealer very sparingly, as will I in the future.

He found a couple of dings in the top of the block, near the rim of 2 and 3 cylinder bores,which could be from the valves hitting the block, and might explain the mysterious noise that started this whole rebuild. The stretched timing chain could have caused such valve crash. As mentioned before, the ratchet noise might be from the same stretched chain hitting the housing.

So now I have it all home, with the block mounted back on the engine stand.

Unfortuately I missed John's free time and the project will be dead in the water until after Christmas. John has foot surgery on Monday, which should have him laid up for a few weeks, and of course there are family Christmas events that demand attention.

My next step is to call Skip and find out what parts I will need. Obviously there is a new timing chain needed, as well as a gasket set. My tappets, or valve lifters were replaced 1000 miles ago and I don't know if they can be used. They look fine to me, but I'd hate to jeopardize my new cam. I look for advice on replacing the pushrods.

Should I replace the manifold and cylinder head studs? This would be a good time to upgrade my oil filter to take disposable canisters. What else do I want to do now to avoid problems later? I took the cover off the transmission and gazed at the gears for a while. I don't see any chipped or worn teeth and except for the rattle in the remote shifter (and a tendency to grind when I am impatient or have the clutch poorly adjusted) the transmission performed well, so I guess I'll just put things back together. Part of me says I should disassemble and replace bearings and seals, but the job does seem intimidating.

I'll post again after I've talked to Skip about parts purchased so far

Part six - Bills are due

[Part 1][Part 2][Part 3][Part 4][Part 5]

Date: 13 December 1997

Got a bunch of parts and the bill for parts supplied so far, and it came to $1700. That puts me right at the budget of $4000. The engine is still on the stand and other incidentals are sure to crop up.

I replaced the tappets, as advised. The rod bearings are new also. In retrospect, my limited engine work done during the restoration was redundant, costly, and possibly contributed to the demise of the engine.

Since I wasn't ready to remove the engine (and knew that compression and oil pressure were satisfactory) I dropped the oil pan and replaced the rod bearings. I also replaced the tappets and cleaned up the rocker arm.

I've already confessed that the machinist found silicone gasket seal blocking part of the oil pump. The rod bearings look only a little better after 1000 miles of use than the ones I replaced, and the tappets, which cost $150, can't be reused.

The oft repeated advice of not starting a project until ready to do it completely echoes in my ears.

Looking ahead, we are ready to assemble as soon as John is on his feet (literally). I need to check with the machinist to see if he torqued the small end bolts on the rods (I assume he has.) The oil pump is completely assembled, as is the reground cam shaft. We need only to install the pistons and the head along with the oil pan (with less silicone sealant). Timing gears and chain might take some time, also.

Meanwhile, as Christmas settles down, there are always plenty of things I should do on the chassis. With the engine out of the car I can redrill the mounting holes for the hood attachment brackets, which never lined up properly after reassembly.

I have committed to installing a brake servo, which should be easier with the engine out. I have a Lockheed servo designed for the Mini which should do the job nicely. I need to move the left sided horn over to the right (where the second fuel pump goes on a Mark II) and the servo should fit.

Upgrading my Mini with a similar unit went a long way in increasing my comfort and confidence in the car. I've agonized some over the originality thing, but Safety Fast includes stopping fast.

I need also to reposition my steering wheel. When I had the steering gear apart I reinstalled the cloverleaf flange on the pinion shaft in a positon that ultimately didn't allow for the steering wheel to be oriented properly when the front wheels were aligned. I should be able to pull the flange off and rotate it about 45 degrees.

I will take the advice of reinstalling the transmission untouched, as it seemed to be okay before all of this.

Is there anything else I should do with the engine out? (I already did the whole brake and suspension system during the frame off part of this.


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All pictures courtesy of Andreas Pichler.

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