| Author |
Message |
    
David Saville
| | Posted on Sunday, 30 September, 2001 - 12:25: |    |
In the Silver Cloud 1 6 cyl. I understand there are liners in the block. Is this correct and can a new one be purchased and hydraulically pressed into place? Is this dangerous with a cast block i.e. cracking etc.? All this to save a rebore so the standard sized pistons can still be used or does the cost factor make it less expensive to rebore and use oversized pistons.
Dave Saville |
Bill Vatter
| | Posted on Sunday, 30 September, 2001 - 20:47: | |
A Cloud has full-length cylinder liners made of hard steel that can be removed and new liners pressed in. They are removed by boring very slightly less than the OD of the liner. Then, the remainder of the liner is split with a chisel and peeled it out. A replacement liner can be pressed in. In the US a good machine shop can do this for about $100 (US) per hole. Replacement pistons also cost about $100 (US) per hole (some variation on this). I have heard the best replacement pistons are made in Australia, better than RR pistons which are significantly more expensive.
However, it is quite acceptable to bore the cylinders oversize and fit oversize pistons up to a maximum oversize of +.040 inch. Removing the liner should only be necessary if the cylinder has suffered damage rendering it impossible to refinish within the .040 limit.
You may have heard removing the liners discussed in the context of the earlier 4.6 L engine. These engines had a short liner at the top of the cylinder only. This was originally done because most wear occurs at the top of the cylinder where the pistons have greatest side thrust. The short liner can also be bored oversize, but this is not the best solution. Uneven wear at the interface between the hard liner and softer iron below causes problems. Therefore, conventional wisdom is to bore out the liner and refit a full-length liner to standard size. |
Jim Bettison
| | Posted on Sunday, 30 September, 2001 - 23:44: | |
I have been told that RR looked very critically at their practice of fitting short liners and that experimental engines were produced (particularly at about the time of the S1) which had full length cast iron liners. The problem with the quarter length chrome liners was that at the junction of the liner and the bore there was a tendency to produce a step in the transition, which tended to be self-propagating.
At about the time of the RR "B" series engines Rover were working on, and used in production, a chrome-flashed bore in the Series 1 Land-Rover engine (also a o/h inlet, side exhaust engine) and it wasn't a good idea either.
I am fortunate that the maker of the pistons referred to by Bill is about 15 minutes from where I live in Adelaide (for info on these pistons look at www.jp.com au). A common practice is to replace the liner, as Bill has described, and hone to a standard size, as you then choose; then, measuring the bore(s), you order from JP Pistons a set of pistons to suit the nominated bore size(s). Pistons come complete with rings and gudgeon pins. Then it's a normal check and fit job.
I understand that some persons here have successfully machined the existing liners and bores to an oversize by _honing_ the short top chrome liner, and the rest of the bore, using _soft_ honing stones (which will, of course, cut the harder chrome at a greater rate than they will cut the softer iron lower section). Again, once the cylinders are honed to size, you proceed to order to the size(s) from JP, and fit, etc. In any case, I would recommend that you contact JP and discuss the way to go with them. You'll find them helpful, and with the $A where it is, particularly attractive for overseas purchasers. I think a set of 6 pistons, etc, will cost around $A1,000. (By the way, I have no commercial association with JP.) My only comment is that it is worth nominating that the pistons should be matched within a defined weight tolerance; their casting technique can introduce some significant variation between units.
Good luck. |
Richard Treacy
| | Posted on Monday, 01 October, 2001 - 20:56: | |
The short Brichrome liners were a nightmare, and guaranteed broken rings as soon as any bore wear occured at all, producing a ridge at 2 1/4 inches. Early Mk VI cars were flash chromed at the tops of the bores to a depth of 0.0015 inches, and this was even worse and many were rebuilt with Brichromes under warranty. Hell.
In my opinion, patching up bores with quarter length inserts is just throwing good money after bad, producing a result destined to fail in a few tens of thousands of miles.
The only proper job here is to fit full-length liners.
I believe practically all Mk VI, Silver Dawn and R-Type cars have full-length liners fitted by now.
I bought full-length liners for my R-Type many years ago (1980) from RR, but believe they were and still are produced by Hepworth in the UK for RR. They are 0.062 inches thick, and can be bored to as much as 0.040 oversize, although mine are still standard. When I had them fitted, I discovered that two cylinders had 3/4 length inserts as well as the Brichromes, factory fitted probably because the lower bores failed inspection. They were a bit tough to machine out, but REPCO managed and the new full-length liners fitted just fine. I have never broken a ring since, but later replaced the RR sourced pistons by far superior REPCO injection die cast and tin plated solid skirt pistons with Jaguar (read Holden 186!!) rings which stop oil consumption completely. REPCO probably still has a listing for 3 5/8 inch bore motors (is it TC104?).
Yes, JP Pistons are also extremely highly regarded, and are world renouned. However, I believe they are sand cast and hence not quite so good as injection die cast pistons. Any comments ? Am I wrong ?
RT. |
Jim Bettison
| | Posted on Tuesday, 02 October, 2001 - 10:55: | |
I didn't make clear in my previous posting that I would only contemplate full length liners if doing a job of reconditioning. Part liners and chrome plating - no, never. The honing process I described seems to me to be less desirable than full liner installation.
About JP pistons: I don't know whether they are pressure cast or gravity cast. I understand that pistons for 3.5" or 3.625" engines are basically the same casting, the actual configuration being decided by amount of machining. I know that they can do variations on a standard piston (e.g., in the crown shape) by varying the moulds. I've taken the view that the proof of the pudding (for which read piston ...), etc. |
David Jones (210.8.232.4)
| | Posted on Tuesday, 27 November, 2001 - 19:13: | |
We have just completed a full engine overhaul on my Cloud 1. This has included the removal of the old liners and replacement with new ones that had been made by the machine shop out of spun cast iron.
Fitting of JP Pistones etc completed the job.
The local machine shop was able to remove the old liners and install new ones without any problem.
As for the JP Pistons we have not had any problems as yet.
regards
David Jones (Perth) |
David Saville (203.166.96.235)
| | Posted on Wednesday, 28 November, 2001 - 07:59: | |
We have also done the same as David Jones with our Cloud 1 and should have done it in the first place. A reputable engine rebuilder on the Gold Coast replaced liners etc and JP Pistons were very prompt with supplying replacements. Engine is now running how it should and will last another lifetime.
Regards
David Saville |
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