Uneven compressions

C

christopher storey

Member
On my newly acquired 2000 TC, 82000 miles probably genuine , and engine apparently untouched, I noted poor idle. The engine has not used any appreciable amount of oil in 350 miles and there are no apparent signs of blowby into the crankcase . The inlet tappet clearances are all within limits but the exhaust ones on nos 1 and 3 cyls are 7 thou and 9 thou. Hot full throttle compressions are 150,166,121,150, so no 3 is clearly adrift. Adding 15 mls of redex to each cyl and repeating is slightly worrying in that each reading increased by 28 to 32 , but the evenness of the increment does not suggest to me that this is a ring problem . Do I just pull the head , or should I be thinking of pulling the pistons as well ? ( if the latter I am inclined to pull the whole engine as it will need a new starter ring before long - 3 teeth missing ) . All advice gratefully received
 
I don't think the tappet clearances will make any difference to the readings, but they could affect the idle, (but probably not by much), the increase after the Redex would point to the rings (has the engine been standing for a long while? If so the rings could be sticky in the grooves) but No3 has probably got a valve problem as well. You'd have to remove the head to get the pistons out, so that's the starting point whatever it is.

If I was doing the head, rings, and ring gear, I'd do the lot without pulling the engine, but that's just my choice.
 
Harvey - many thanks . I suspect that the engine has only done 600 miles in the last 25 years so gummed rings is a distinct possibility . However, I also di a home made leak down test, and with 100psi into the cylinders I could not hear anything coming out of the dipstick tube , and indeed the engine turned over under the pressure . Are there any particular snags to pulling engine and box together ? I am nearly 70 now and prefer to work standing up !
 
christopher storey said:
Are there any particular snags to pulling engine and box together ?
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That is the way it's supposed to be done. I've always done most things in-situ, but when I have removed the complete unit I've never had problems, (although I have heard of gearbox remotes being broken when doing it, but I can't really think how....).
I just raise the rear of the car on stands when lifting it out and it lowers the bonnet locking panel, and reduces the angle needed to get it out from under the tunnel.
 
Out of interest, what are acceptable compression variations across cylinders on a 2000tc?
10% difference?
Jim
 
The plot thickens, unfortunately . Head off, head and gasket looked ok, certainly no overt blown gasket, nor any signs of serious valve deterioration. Bores do not feel to have any undue ridges in them . However... the no 3 cylinder, which was the suspect one, has a very strange rusty discolouration on the walls. I do wonder whether it has sat with water in it at some stage . Opinions as to cause, and/or where to go from here, will be very welcome . Pics will be posted shortly



 
I'd fill the two bores with the pistons at the top with paraffin, noting the amount, and then put the same amount in the others, and see how fast it disappears.

I'd try and clean the mark on No3 bore a bit, and I'd consider popping that piston out to look at the rings, (and the rest tbh) particularly if the paraffin disappeared out of that one first. For that mark to be created by water I would think that the engine would have had to have been standing on it's end while it was in there because it doesn't look like it spreads all the way around.
You can buy hones pretty cheaply.
 
Looking at the 2nd photo in your post (and taken the liberty of copy-and-paste, rotated, and marked the area in question!), is that a crack in the cylinder wall? (which I have 'looped' [my free hand mouse skills aren't that good!])
 

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darth sidious said:
Looking at the 2nd photo in your post (and taken the liberty of copy-and-paste, rotated, and marked the area in question!), is that a crack in the cylinder wall? (which I have 'looped' [my free hand mouse skills aren't that good!])
Click to expand...

I can only dream of having computer skills like that!

I think a quick clean up of the bore should tell, but if it is a crack that's unusual, and is going to put an end to that block.
 
Well, I cleaned it up with some abrasive, but there is no crack that I can see . However, right round the bore at the level of the discolouration and lower is a most peculiar lumpy feeling, which I can only put down to erosion of some kind. Preliminary discussions with the engine man that I use for engineering jobs suggest that it may be repairable, possibly by sleeving which we have done in the past on XK blocks but he will need to see it first. I am slowly working towards the engine out, but I do have problems with overhead clearance with my engine crane so I think I shall try and remove the engine first and leave the box till later . Thanks to everyone for their advice
 
Engine now completely stripped. Curiously, viewed from the crankcase, the cylinders all look as though there are liners inserted . Is this an illusion, or was it done at the factory ( no reference in workshop manual ) or could it be a later engineering shop mod
 
Well, the problem is now clearly identified. No 3 cylinder bore looks like the mountains of the moon !



Incidentally, all 4 cylinders appear to have been lined, and the man who does my engines says that he has seen quite a few Rover engines ( not necessarily P6) with liners from new - it appears that it may have been a way of using a block that may have had some casting deficiencies
 
I'm not sure if it has had liners, whether what I was going to suggest would be feasable, but with a 2000 block in that condition I'd be inclined to overbore it to take standard 2200 pistons.
 
I did wonder about that, but 3 questions arise

1. Wouldn't it be very expensive to take out something like 180 thou ?

2. Wouldn't it also leave the walls rather thin ?

3.Are the 2200 pistons flat topped? ( and is there a risk of valve clashing as a result )

I am sorry to ask stupid questions , but I know absolutely nothing about the 2200 block castings etc
 
christopher storey said:
1. Wouldn't it be very expensive to take out something like 180 thou ?
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Once it's all set up I can't see it being much more expensive than a standard rebore. IIRC I worked it out at 183 thou, which is 91.5 a side, which wouldn't be a problem as standard, but might be if you have liners fitted.


christopher storey said:
2. Wouldn't it also leave the walls rather thin ?
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A standard 2200 is only an overbored 2000.


christopher storey said:
3.Are the 2200 pistons flat topped? ( and is there a risk of valve clashing as a result )
Click to expand...

2200 pistons don't hit the valves on a standard engine, so wouldn't hit on an overbored block fitted with a 2000 head.
 
Harvey, thanks for the prompt answers. However, I gather the 2200 conrods have a narrower little end, and I would have to machine my rods to fit , so I think I will probably stick with 2000 pistons of some size
 
christopher storey said:
so I think I will probably stick with 2000 pistons of some size
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Providing you can get a set of oversize pistons with rings then that's probably easiest, providing the marks on that bore aren't deeper than the rebore goes.
 
Harvey : the depth of the mountains of the moon certainly looks to be a problem, but Westwood liners are ace at coping with this sort of problem. It may be that the answer is to fit a new liner and bore all 4 to +.010"
 
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