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MG TD TF 1500 - Engine experts wanted

I have a noise in the engine that goes away as the engine revs up. I think and have two mechanics agree (not LBC specialists) that it sounds like wrist pins. When I rebuilt the engine I changed everything but the wrist pins. Assuming it is the wrist pins I have a plan that I need a reality check on. The engine is in the car as well as the transmission I may remove the engine but I may try something different.

I would remove the oil pan and undo the wrist pin clamp bolt from the piston. I'd the disconnect the rod caps and push the piston up out of the cylinder far enough to remove the wrist pin (if it will go that far). Then replace the wrist pin and tighten everything back up. I would hold the piston with a strap wrench while tightening the clamp bolt. The pistons are .100 over and I've been told they won't come out with the crank in place.

If you are just going to tell me to remove the engine that is my ultimate option. If you have any advice on my plan thanks for contributing.

The oil pressure 50 when the engine is hot and goes to 70 when revved. If you think the noise is something else here are the measurements I've made:

Cylinder Diameter
#1 2.722 in
#2 2.723 in
#3 2.721 in
#4 2.724 in

Compression
#1 132 ft/lbs
#2 140 ft/lbs
#3 138 ft/lbs
#4 130 ft/lbs

Any advice would be greatly appreciated.

Tim
TD12524
TW Burchfield

I think wrist pins are fitted to the individual Pistons. Sometime through selective fit.
I think, if it is wrist pins you will need to get new Pistons, pins, and rings.

Jim B.
JA Benjamin

But the MG-T engines do not have wrist pins. They have Gigion (sp) pins. The wrist pin is tight in the piston and loose in the connecting rod. NG-T pins are free in the piston and clamped in the conn-rod.

I am not sure about the fit in the piston and if its selective but I still think the pins are matched to the piston.

Jim B.
JA Benjamin

What testing ... if any... was used to determine that the knocking was the pin?
MG LaVerne

Tim, in your previous posting on this subject, I saw several inputs that said your cylinder bores might be OK as you measured them. At this stage it may be time for a reality check.
Those cylinder bores all exceed the recommended .003" maximum piston clearance for a serviceable engine. While I agree that cylinder taper is a worse situation to ask rings to handle, a bore that allows the piston to rock in a bore and slap on the thrust side is another concern. I suspect that condition may be what your hearing. Normally piston pin noise doesn't go away as rpm increases.

Since your already at .100" over size, there's not much to do to easily and permanently solve the problem.
In past years, some machine shops would knurl the piston skirt to bring the clearance back in range, but it was considered to be a less than desirable fix, because the rings were usually also looser than preferred and oil blow by was another concern..

Tim, get some advice from other experts, but I believe if it were my engine, I'd begin to accept the probability that it is time to re sleeve the block and put new pistons in properly sized/finished cylinders.
Richard Cameron

Hi Tim,

Sorry, the gudgeons can not be removed as you would like. I did know that, but I have been to my shed and checked! A conrod poked up a bore as far as it will go won't go far enough for the gudgeon to be removed from above. Even if the bolts are removed, only about half of the gudgeon will protrude above the deck. I tested a standard rod in a block bored .125". It looked as if it might be close to possible in a 72mm (XPEG) bore, particularly if the rod is filed smooth and/or if the bore is oversize a bit.

I know 1250cc pistons can be taken out from below but 1366cc pistons (.125" o/s) can not. Next time I dismantle a 1366cc engine I am going to investigate grinding off / chamfering bits of the crank to allow the pistons to be removed from below. It should only be a .125" chamfer needed! Of course this would have to be done BEFORE balancing the crank.

Good luck with your search for the elusive noise. Your rocker shaft isn't slopping up and down in the pedestals, is it?

Bob Schapel
R L Schapel

Hi Tim,

Just remembered another important point. Gudgeon bolts should always be tightened with the gudgeon held firmly. I put a bolt through the gudgeon and clamp the bolt in the vice (on a slight angle so twisting action doesn't loosen the rod in vice). Tightening gudgeon bolts with the big end taking the strain could twist the rod. Undoing is worse as it usually takes more torque to "crack the seal".

Incidentally, conrod bolts are 8mm and 27lb/ft is said to be recommended. An old MG expert told me this is too much and so I use less torque. Gudgeon bolts are also 8mm. The 33.3 lb/ft recommended is ridiculous! They should be tightened to the same torque as the big end bolts. Both are 8mm with 1mm pitch threads. Higher torques might be ok if special bolts are fitted but not with originals. Bolts should always be checked for stretch. Stretched bolts are a liability!

Bob Schapel
R L Schapel

Tim, your piston pins can be removed from the bottom of the engine. Recommend you consider doing the following option: Push the piston up out of the bore to expose the rings. Carefully remove rings( easily broken if not done carefully). Remove the pin clamp bolts. Pull the piston/rod assembly out of bore from bottom enough to remove the pin (a hot air gun will make it easier to remove a tight pin). Remove rod from bottom. Push the piston without rings out the top of the bore. (keep all of the parts for each cylinder together so you can evaluate/inspect them).

OK, 1. After getting the pistons out, more carefully measure cylinder bores and look for damage scratches etc.
2. inspect the pistons for worn ring lands and skirt wear at thrust faces. Check pin fit in pistons(a snug fit by hand). Measure pistons at thrust skirt below pin hole for fit in each cylinder bore (check all 4 individually).
3. Given that you have already experienced some piston/pin slap with the combination of existing pistons, with your new measurement data and inspection --its time to decide on a possible course of action:

Don't want to pull motor yet? Well, A new out of the box piston ring package could possibly help by reducing the piston to cylinder wall clearance you currently have with worn and used? parts. Some pistons coming from after market manufacturers are a little tighter out of the box than originals especially in the .100" range. size. I personally saw this in one of my engine builds. Also, a 4 ring piston might be better if you can find new ones in the required size. This option is a gamble, could cost you a few throw away bucks and may not last as long as a preferred bore refurbishment. However, it might allow you to kick the can down the road for a while. Be sure to remove any wear ridge at top of a cylinder.
Preferred Option, Depending on your closer examination and findings etc.--- re line (Sleeve) all of the cylinders and use new standard pistons after a full engine tear down.
Richard Cameron

Bob, I agree, as do many engine builders!
Len Fanelli

The only dimension that matters is the actual piston to cylinder clearance, as measured appropriately. There is often piston to piston size variation. Agree with the above, esp. that I doubt a piston pin and even if so you need new pistons/pins matched to each other. Did you ream the ridge at the top of the cylinder? George
George Butz

MG LaVerne. Testing consisted of pulling plug wires one at a time (engine running), stethoscope, compression, oil pressure and bore measurement.

Richard, I plan on measuring the piston bore clearance below the bottom oil ring as recommended. A re-sleeve is always an (expensive) option. I did install new rings when I rebuilt the motor but used existing pistons. Good idea for removing the pistons.

George, there was almost no ridge at the top of the cylinders. I did remove what was there, however. I also honed the cylinders.

Time to start the tear down. I'll no doubt be back with more questions and observations. I sincerely appreciate you all taking the time to offer advice and insight.

Regards
Tim
TW Burchfield

Tim,
I am not an expert.
Last winter, with the engine in the car, I removed the pistons and rings with the crank in place. I had other reasons than yours for doing this. I cleaned and honed the cylinders, new pistons and rings. New cam and roller lifters etc.
In my case the car runs great but has a lot of blow-by(Supercharged).
I am now going to remove the engine and bore the cylinders.
I should have done the complete job last winter and pulled the engine. Alas, part of the learning curve.
Just wanted to let you know that you can remove the pistons with the engine in the car and of course with the crank in place. Just a lot of push, pull, rotate and juggle. But is it worth it?
Mort
TD 1851
Mort 50 TD

I would not mess about with the engine in the car.
On a TD engine removal is simple and quick compared to the TF.
To make life easy, remove the sump and associated clutch rods. Turn the crank until pistons halfway up the bore, jack under the bell housing and the motor will clear the rad support without strain. Maybe you have to pull back the steering column on LHD cars.
I can get my TF engine out this way and it's much easier on a TD.
Ray TF 2884

Ray Lee

Mort, my pistons are .100 over. I've read that anything over .060 is impossible to remove with the crank in. What do you think?

Tim
TW Burchfield

Ray, I really have no excuse for not taking the engine out. The body is off the car and everything is accessible. I just thought it might be easier (or at least less time consuming) to do the repairs with the engine in the car. On the first rebuild I was trying to save time and money. Of course I did neither.

Tim
TW Burchfield

TERMINOLOGY varies by country

Gudgeon pin

In internal combustion engines, the gudgeon pin (UK, wrist pin US) connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot upon.
Sandy
Sandy

Further thoughts: the pistons would have to be really sloppy in the bores to tap and make noise, and I would think that would diminish as the engine warmed up. I would check for several other things that could make the noise. Many new pistons protrude above the block deck, make sure not piston to valve or head contact. Check for bent pushrods/loose pushrod ends, sticky valves, bellhousing bolts that are too long. Check rod/main bearing clearance with plastigage with caps torqued correctly. There have also been past issues with incorrectly cut cam gears as well as oil pump shaft circlips. Just some stuff to check. Even things like exhaust manifold leaks can make weird noises. George
George Butz

George, I used the pistons that were in the engine as they seemed to be in excellent condition (visually). The head is off and I just checked for any contact between head and pistons and see none. I'm going to remove the pan/sump this evening and check that the wrist pin/grunion pin cinch bolts are on the correct (right) side of the engine. I was sure I installed than that way but It is one more thing to check off the list. I tore down the rocker arm assembly last night and found the shaft to be in pretty poor condition. I've ordered the parts for a rebuild. BTW the sound is similar to a rattle, not a knock. Thanks very much for taking the time to brainstorm this issue.

Tim
TW Burchfield


When you mentioned a rattle sound-- that brings to my mind the possibility of a timing chain tensioner that has a plugged oil pressure hole. The tensioner has an approx. .039" hole drilled to allow oil pressure to exert force on the slipper of the tensioner. It is common on old engines for this hole to be completely plugged up with carbon/sludge. It must be cleaned out with a very small drill bit to allow the tensioner to work properly again. If not clear, the chain will rattle, and sometimes contact the aluminum cover with resultant noise.
Richard Cameron

Mort, if doing a rebuild and your engine is supercharged, I would put in custom rods and pistons, I did this on my car. Venolia Pistons, Crower Rods. built for my car which is bored eighty over. the pistons were beefed up on top due to the heat generated by supercharging. modern is better. no grudeon pins to mess with and modern steel rods are much better that those original rods in the car.
TRM Maine

Richard, I disassembled the timing chain tensioner when I rebuilt the engine and cleaned it thoroughly. Of course that doesn't mean that if I tear the engine down again I won't check it again. Buy using an automotive stethoscope the noise was located in the upper block area. That was one reason we thought it was wrist pins. Thanks very much for the suggestion.

Tim
TW Burchfield

Tim,
My pistons were +.060" over and I did not have much trouble with them. Again, I am not an expert but just from memory I can't see that another .040" would make a difference.

Tom,
Thanks for the input. New pistons and rods are on my "to be considered" list.

Mort
Mort 50 TD

Mort, thanks. The worst it could cost me is a few well chosen words I learned from my father. :-)

Tim
TW Burchfield

This thread was discussed between 11/11/2015 and 12/11/2015

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