From: PIETER.POSTHUMA@nlrtm.ponl.com
Date: 09 Nov 1998 14:08:52 +0000
Subject: [imps] Pistons in STD 875.
Can somebody please advise on the following. I have a standard IMP 875 engine. The crankshaft is ok but the cilinders need boring to +030. I only have +040 pistons (new). In the various books on Imp engines it is stated that untill 030 no problems will be encountered but going to +040 there is a change that the cilinderlinings are not exactly vertical in the block so you risk the chance of boring through the cilinderlining wall.
Is this a real risk, I mean does somebody have any experience with this happening or should I just ask my engine workshop to go ahead and see where the block ends up.
If the above worst case would happen would there be any means of reclaiming the block ?
Please to hear your advise.
Regards
Pieter
From: Nickcleak@aol.com
Date: Mon, 9 Nov 1998 15:00:40 EST
Subject: [imps] Re: Pistons in STD 875.
> the chance of boring through the cilinderlining wall
I don't think you will have a problem , i've seen a lot bored + 0.060 "
nick ...
From: TMo5018257@aol.com
Date: Mon, 9 Nov 1998 15:16:10 EST
Subject: [imps] Re: Pistons in STD 875.
Regarding overboring Imp 875 blocks past +30 thou.....
I too have seen blocks bored +60 thou, but and this is a big but.......
>From information from George Bevan, some blocks had their liners cast in not quite perfectly straight. We are not talking about huge discrepancies but enough to make boring the block a problem.
With engines built like this, as the cast iron liner is not square to the cutting edge, there is a chance that the boring process will go through iron into the soft alloy behind it.
Then there is another problem, if the liner is that thin there is a chance of minute movement, this can cause problems with sealing the head gasket.
This block may be fine, but there is a possibility of complications. It may be worth obtaining a set of +30 thou pistons as I have been told that this is the maximum safe overbore.
Cheers,
Tim
From: PIETER.POSTHUMA@nlrtm.ponl.com
Date: 10 Nov 1998 10:45:31 +0000
Subject: [imps] Re: Pistons in STD 875.
Thanks for the replies, I still have to get used to the fact that I donot see my own e-mail being return via onelist.
I just got a call from the Engine Shop that they had done the re-bore to +040 and all went well. They where surprised a bit about the iron liners having been moulded in the surrounding alloy. The top 1 mm or so was alloy so when they started boring they first got alloy boring particles. They also flattened the block.
So now it is back to my workshop to look which of the 6 cilinderheads I have lying around is the best. Does anybody know the standard height of a cilinder head ? This so I can measure which ones have already been skimmed.
I intend to have a unleaded conversion done to it. And put in new valves which I bought for for next to nothing at Beaulieu (UKP 1,5 for 8 BRAND new ones) last september.
Any other things I must watch out for when determining which head is the best ?
Regards
Pieter
From: Gary and Carol Henderson
Date: Wed, 11 Nov 1998 00:15:40 +-1300
Subject: [imps] Re: Pistons in STD 875.
Hi Peter
Avoid a bowed one. If you can't, it must be straightened as well as possible in a press, not just planed. This is to avoid the cam-bearings being out of alignment - if they are, your camshaft will last only 5000 km or so....OK, it might be feasible to plane the bed of the cam-carrier as well - not sure. (Comment Nick?)
Certainly, for Japs that run cam direct in the head casting, bowing is fatal.
Usual comments re mouse-holes in the waterways, and crack-testing is routine. (Rootes never seemed to have any serious incidence of cracked heads.)
Good luck
GaryH
From: TMo5018257@aol.com
Date: Tue, 10 Nov 1998 08:48:19 EST
Subject: [imps] Re: Pistons in STD 875.
Hi all,
>Rootes never seemed to have much incidence of cracking in cylinder heads.
Er, kinda disagree.....
Sport Heads are renowned for cracking between the spark plug holes for cylinders 2 and 3.
I have dumped several heads that have had internal cracks, leading to gradual water loss, mainly in L4 type engines (late standard cars with the oil drain).
I also do not understand what you mean by the head bowing and not being salvageable by skimming. I've fixed god knows how many head gaskets through warpage, and each time the face has been brought back to true, the engines have run fine. The only problem area lies in increased compression ratios if the head has been skimmed many times before. This of course can be remedied by 'decking' the pistons, to bring the ratio down (only warranted if the head is something special, otherwise fit a replacement).
The cam shaft runs in it's own carrier which bolts to a flat top surface; you would have to get the head to thermo nuclear temperatures to warp the cam carrier, by which time the engine will have stopped running anyway.
Maybe I'm missing the point of what you were saying, Gary. But skimming does work.
Cheers,
Tim
From: Nickcleak@aol.com
Date: Tue, 10 Nov 1998 15:50:26 EST
Subject: [imps] Re: Pistons in STD 875.
> Any other things I must watch out for when determining which head is
> the best ?
The Sport Head is the best if you are lucky to have one !
The others all perform the same although the latest L4 head has more metal where it's needed . You may get one at Speedy Spares for £40 ..
I have just had one modified by Ian Carter for my Turbo engine , he was impressed by the quality of the head ..
Nick
From: Nickcleak@aol.com
Date: Tue, 10 Nov 1998 15:50:29 EST
Subject: [imps] Re: Pistons in STD 875.
> Avoid a bowed one. It must be straightened as well as
> possible in a press, not just planed.
indeed ,.. Ian Carter always planed the top surface as well as the head face ..
I think pressing it would crack it though ...
Nick ...
From: Nickcleak@aol.com
Date: Tue, 10 Nov 1998 15:50:31 EST
Subject: [imps] Re: Pistons in STD 875.
> Sport Heads are renowned for cracking between the spark plug holes for
> cylinders 2 and 3.
Is this on standard blocks or wet liner 998 blocks ??
Remember the liners USED to be 0.002" higher than the block , but this practice stopped around Early 1980's .. at Hartwells anyway ..
> The only problem area lies in increased compression ratios if
> the head has been skimmed many times before. This of course can be remedied
> by 'decking' the pistons, to bring the ratio down.
the higher the compression ratio the better :-) sorry , that's just for me !
> you would have to get the head to thermo nuclear temperatures to warp the cam
> carrier, by which time the engine will have stopped running anyway.
I have seen alloy engines ( not IMP ) overheated so much that the wiring insulation on engine wiring and Plastic cam cover has melted due to heat from the block ! Todays motorists just drive until it stops , warning lamps or no warning lamps ! ( they never pump up their tyres either , always about 8 - 10 psi low ) come to think of it they never open the bonnet between services ..
nick ..