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MG TD TF 1500 - TB Timing Chain Tensioner Question

I'm curious, and it seems germane here: early XPAG engines as installed in TB cars in 1939 had no timing chain tensioners - was the pad present but un-drilled, as shown in the Timing Chain post? What chain was used without a tensioner; the chains usually supplied for XPAG engines would be flopping all about, no?

I have a TB with a "factory" replacement engine, and a part of me would love to find another TB engine to replace it as closely as possible. The thought of running without a timing chain seems pretty dodgy and would lead to variable timing, but the thought of having an engine without the tensioner bump would be very unusual.

What do (did) other TB owners do?

Tom Lange
MGT Repair
t lange

Tom,
I have an engine without time chain tensioner. I borough it as a XPAG engine for MG-TD. The mysterious is, that the engine Plate and as well the cover have all the precautions for the tensioner body, except the attachment holes and the oil feed line.
During refurbishing of the engine I decided to install the tensioner as it original is on the TD.
My problem is where can I get the oil pressure? I do not know where the oil passage is to feed the front bearing?
Can you help?


GK Guenter

An alternative is to load the tensioner with a spring.
Dave H
Dave Hill

In reality, the XPAG tensioner is spring loaded.

There is the tiny hole feeding the tensioner and a larger hole where it runs out on the chain. Oil is for lubricating chain and does not apply load in the tensioner.

There have to have been a billion engines running cam chains with no tensioner or oiler. Many millions of Chevy engines, alone.

Engineers today have cheapened it down to timing belts that are designed for expensive replacement or else fail with time and chains with tensioners that self destruct. Sad. Planned obsolescence.





JIM N

Jim, thank you for your comment. You are right, there is a spring inside the tensioner body which move the tensioner itself against the chain. Unfortunately this spring is very soft and I don’t believe that this spring can tension the chain if the engine is running.
Sure, the engine can run even without tensioner but this will create a nasty noise.
Cheers,
Guenter
GK Guenter

Günter

may be the spring is too soft for tensioning but I guess it is sufficient to keep the chain calm.
W_Mueller

Guenter,
Not quite true. As long as there is no slack there will be no noise. The Morris Minor never had a chain tensioner although I retrofitted one on mine. Perhaps this one could be adapted for the XPAG. It has been on there for the last 10 years
Regards
Declan

Declan Burns

Hi Tom and GK,
I have a pre-war Morris 10 engine (virtually identical to XPAG but 1100 cc) in my shed. It does not have the tensioner bump on the timing cover, so obviously is similar to the TB. However, it does have that bit of extra metal flange on the side of the block casting near the word "self" in GK's upper right photo. If I had a TB, I would go without the tensioner to keep it original. I would use a good quality chain and, if it was a bit noisy, I would accept that as normal for a TB. I guess if the block has been tunnel bored, it might loosen the chain and increase the noise.

Tom, Do you have a timing cover without the bump? I am guessing they are hard to find. Most people who have them, probably have a complete engine and don't want to sell off bits. Perhaps someone should have some cast, using an original as the pattern? If you start a new thread on "Pre-War", you might find some solutions or gauge interest in having some cast.

GK, The oil supply for the tensioner on the TC/TD/TF blocks comes from the front main bearing. The middle and rear mains have one oil hole supplying them but the front has one supplying and another feeding the tensioner. That is why the upper halves of the front and rear bearing shells have two holes. (Only one needed at rear but to prevent wrong fitment.) Yes, your photo shows a thick "web" which is where the oil passage is drilled in TCs etc.

Bob
R L Schapel

The timing pointer on my pre-war engine is not like a TC. It is like the one on page 57 of the brown TC Workshop Manual. If you look at it closely, it is obvious there is no bump on the timing cover in that photo. It is a cropped photo, but the lower part of the bump would show, if it existed. It must be a TB photo in the TC manual! I just went to the shed and measured the distance from timing pointer rivets to top bolt. It is about 140mm on the pre-war and about 120mm on a TC because the rivet "platforms" are cast in different positions.
R L Schapel

Thank you for all information’s.
@ Declan, I have an original TC/TD tensioner that is not the point, but I would like understand how it works. Where the oil is coming from. I’m quite sure that the original spring is not able to hold the chain tensioned.
@ Bob, your information seems to me logic. The front bearing get the oil and distribute it inside the big web. Do you know if this hole inside the web was drilled or core casted?
Thank you Guenter


GK Guenter

Guenter,
Even without the tensioner the chain will assume the curve. (Google photos of motorcycles at speed).The chain tries to follow the teeth around the chain wheel. The tensioner just stops it thrashing around due to cyclic changes.
Ray TF 2884
Ray Lee

OK Ray, but please tell me why did MG Build the engines for TA/TB and partial TC without an tensioner and start to install one on later TC and TD/TF. What is the reason behind? BMC was under cost pressure. Any component not installed was a cost saving. Nobody on earth will install a component which is not needed.
GK Guenter

Guenter, I think the hole was drilled but I am not an expert in how the blocks were cast and machined. Tom Lange is better qualified to answer that question. I agree with how Jim N explains the way the tensioner works. I think the spring gives the tension and the oil is just to lubricate the chain.

Bob
R L Schapel

Is somebody here to answer the question? How get the oil into the chain tensioner housing?
GK Guenter

Guenter,
It is a drillway, the tensioner gets it's oil from the timing end main bearing supply. You would need to drill from the inside right up to the tensioner. Think you will need good workshop facilities as it needs to be accurate.
As for the need, it was probably complaints about chain slap. It is also very difficult to fit chain wheels without slack.
Ray TF 2884
Ray Lee

There is a brand new timing chain tensioner for 22GBP on eBay at the moment for anyone who is looking for one.
https://www.ebay.co.uk/itm/MG-TB-TC-TD-TF-TIMING-CHAIN-TENSIONER/233085680126?hash=item3644fd39fe:g:vegAAMXQEgpTFyoD
Regards
Declan
Declan Burns

Declan, they come up frequently with this offer, it is the same source I bought it. Good Quality.
GK Guenter

I come back to this thread again, may be Tom Lange can help:
Main question for me is, is there a possibility to drill an oil channel to make the chain tensioner functional?
Thank you for any advice.
GK Guenter

GK, I am sure it can be drilled. I just measured a block and found it is a 70mm long hole. I would think a good machine shop could do it. But there are other options.

Second option. Has the block got the MG insignia cast on the left side under the generator area? If it is a genuine TB block (VERY RARE) you could swap it for a TD block plus money and make a profit. If no cast MG, it is a pre-war Morris block which started at 1100cc and can only be bored to about 1250cc.

Third option. You could drill the block yourself. The problem is that the drill bit might have to be longer than 140mm because otherwise the drill chuck will foul the block. It might be difficult to get a drill that long unless you braze a rod to a standard drill bit. You would start by using an old main bearing to mark the hole location in the front main tunnel. The hole would then have to be started at 90 degrees to surface but then angled in the correct direction. When deep enough, the hole from the tensioner block would have to be drilled after first checking the exact direction to meet the long hole. (Because the drill might have wandered slightly.)

Fourth option. Leave it without tensioner. It should be quite OK. If it is a genuine TB block this would be my first choice unless I swapped for TD plus $. It would be good to hear from TB (and TA) owners who might know if they are noisy with an unworn chain. A pity the Pre-War and TA, TB, TC threads are not very active!

Cheers from South Australia,
Bob
R L Schapel

Hi Bob, thank you for practical advises.
First option, I checked already with my own machinery in my shop. I can do the drilling on my milling machine. Long drill bits are available, from an aircraft maintenance shop next door.
Second option: The block doesn’t have a MG casted insignia that means it is not a TB block.
Third option: Yes, I would try to drill a channel by myself the point is just to find the right starting location and the angle to drill the oil channel.
Fourth option: Leave it without tensioner, yes this is the logical solution. Maybe I can find a stronger spring and renounce the oil pressure solution.
Cheers, Guenter
GK Guenter

Not sure if stronger spring is a good idea. From memory, the supply hole in the tensioner block is much smaller than the hole in the slipper. (Jim mentions this above.)That means it is chain oil supply only and does not increase the tension with oil pressure.
The starting location is easy to find if you fit a bearing to the front tunnel. The hole in the bearing shows the right spot to start. After getting the hole started, angle the drill directly towards the spot on the block where you will later drill a short hole to intersect the long hole. That spot and the position of the holes for bolts can be marked by copying an original TC, TD or TF block. If you can not access a standard block to get these positions, I am sure someone could make a paper or card pattern for you.
Bob
R L Schapel

This thread was discussed between 26/09/2018 and 14/02/2019

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