10:1 or 9:1 ?

[Demetris]

Is there any cunning way to tell apart the high and low compression TC engines, without removing the cylinder head?

The engine number (9:1) is just an indication that contradicts with i 've been told (10:1) by the seller of the already rebuilt engine.
After more than 80 K miles in my car it still runs fine (touching wood now...) with minimal oil consumption but i am having doubts wether i am running it with the correct distributor and ignition timing. With the ignition timing set at what seems to be 10 deg BTDC and high octane fuel runs fine and efficiently but it is hard to
start from cold as it is typical with overadvanced engines. With the timing set at the nominaly correct 6 deg BTDC there are no starting problems, but on the road it appears that it would go better with some more advance.

 

[rockdemon]

Does rudiger's page help?
http://roverp6.info/engineno.htm

 

[KiwiRover]

No way of telling if the engine's been rebuilt. The only difference is the pistons.
Doesn't really matter, just ignore the book and set the timing where the engine is happiest.

 

[JVY]

Demetris, Googling about, looks like the only way to measure your compression ratio is to take the head off (like this http://www.automedia.com/Checking_Compr ... 020701cr/1 ). This seems like a lot of hassle? If your engine runs well at 10BTDC with no pinking, I would be tempted to leave alone? You could always do the check if/when you really need to remove your head.

Looking at Rudiger's info, I wonder why he doesn't list CR for my 2200iTC 491..... engine? Is it because all 2200s were 9:1?

Though, thinking about what KiwiRover says - is there any markings or other signs on the piston faces that you could spot by sticking one of those little USB cameras down the spark plug hole?

Will garages perhaps have tuning equipment that gives CR readings?

 

[Demetris]

The problem is that without knowing the CR i don't know if the distributor is the correct one.
For example, the distributor on the car when i first bought it, with the original 9:1 engine, was out of a Hillman Imp according to its serial number! :shock:

Now i do use a distributor for a 10:1 engine, but if the engine is 9:1 the advance curve is nowhere near the optimum.
I was also thinking about an endoscope, and if i remember correctly a friend has one, so i might borrow it and have a look at the dish on the piston crowns and compare with the spare pistons that i have.

 

[Vern Klukas]

There was a 10:1 sticker that went on the block side plate, but I've never seen one. They must of fallen off quickly or something.

Yours
Vern

 

[NickDunning]

Looking at Rudiger's info, I wonder why he doesn't list CR for my 2200iTC 491..... engine? Is it because all 2200s were 9:1?

I think so, it's possible they may have done some 7:5:1 low compression ones still for export.

Five star (100 octane) fuel started to be phased out in the mid-1970's, hence why Rover ditched the high compression TC and V8 engines in 1973.

 

[j_radcliffe]

One way would be to see if you can get hold of a boroscope and inspect the pistons. If they are Rover pistons, then they will be marked. You should be able to see a part number. Have a look on ebay for a boroscope. They are quite inexpensive.

The other thing you might want to do is a compression test. If you have a good starter motor you should get 190 plus psi compression. This would indicate 10:1 CR. If you get even numbers, (around 155 psi) but lower, this could indicate 9:1, but could also indicate a weak starter motor. Do the compression test with a good battery, with the motor warm and the throttle wide open.

James.

 

[OrganDoctor]

One way would be to see if you can get hold of a boroscope and inspect the pistons.

Would the pistons be clean enough in an engine which has been run to read numbers?
The other thing you might want to do is a compression test. If you have a good starter motor you should get 190 plus psi compression. This would indicate 10:1 CR. If you get even numbers, (around 155 psi) but lower, this could indicate 9:1, but could also indicate a weak starter motor. Do the compression test with a good battery, with the motor warm and the throttle wide open.

James.

James is correct here. A rebuilt 10:1 done correctly will give close to 200 PSI

 

[Demetris]

I am very reluctant to remove the spark plugs from a hot cylinder head to do a proper compression test.
I am going to order a small camera to see what is hiding in there. I doubt that the part numbers will be legible, but the difference in the depth
of piston dish is quite marked between the two types, so as soon as i will have a look in there, everything will be obvious.

By the way, i am running around for almost a week with what seems to be 6 deg BTDC ignition timing, with straight 95 RON unleaded and it will only pink
if i try to accelerate on 3rd or top gear with the engine below 1000 rpm. Generally it doesn't feel as if it has retarded ignition anymore. :?

 

[Vern Klukas]

Why the reluctance?

Yours
Vern

 

[Demetris]

Hi Vern,
when you unbolt something that is bolted in hot aluminium you will most certainly take the threads out. :shock:
Especially as in my case, whoever fitted the first spark plugs after the rebuilt made sure that they were bloody tight :evil: and whenever i change the spark plugs since then the thread in the cylinder head feels as if it is a little tired.

 

[Vern Klukas]

That hasn't been my experience, and I've been pulling plugs and doing plug checks for years on hot engines. Not that I'm trying to convince you, I was just curious. We all have our little procedure peculiarities born from experience.

Yours
Vern

 

[Demetris]

It took me a long time to reach somewhere but now i am sure that my engine has 9:1 pistons in there.
I actually ordered a USB camera, which took some time to arrive, then the laptop blew up, then i got fed up and borrowed a laptop from work to have a look inside the combustion chambers. Unfortunately the quality of the stills is rather dissapointing as you can see for yourself, but the live view was definitely better.

Comparing the 9:1 pistons of my old engine and a new 10:1 set that i also have, it appears that the depth of the bowl is the same in both cases, but in the high compresssion piston is markedly more narrow, making the valve cut outs in the crown seem rather more wide.

Also, what is obvious from the following photo (and it's clearly mentioned in the workshop manual ) is that the 10:1 pistons have cut outs at the bottom of their skirts.

Therefore if you drop the sump and have a look at the pistons at BDC you'll know what you'll have! I'm not willing to get that involved as now i am sure that my engine has 9:1 compresssion ratio. After all this ties with the fact that it runs fine with straight 95 unleaded at a nominal 6 deg BTDC and probably due to the wrong distributor it will tolerate a far more advanced ignition timing.
I guess now the next step is to find a 9:1 2000TC distributor. Michael (redrover) could you remind me what have you done with your distributor when you replaced the pistons? Did you alter the 10:1 distributor?

As a side note i was happy to find that the combustion chambers and spark plugs were relatively clean, with grey to light brown colours in both sets of cylinders and the crosshatch patern on the cylinder walls was very vivid after 80K miles in my hands.