mad_pete Posted April 20, 2007 Share Posted April 20, 2007 Hi, Just set my V8 block to be re-honed and the engineer chap says cylinder 2 has a mark in the piston ring area in the bore. He says its not "too bad" and I haven't seen it yet. Any advice ? Ignore it ? New liner ? New block ? I am not yet well versed in the world of what you can get away with the inside the engine. Thanks Quote Link to comment Share on other sites More sharing options...
mad_pete Posted April 21, 2007 Author Share Posted April 21, 2007 okay I went to see it. It is a rough area at the top of the piston stroke. I think what happend is the gasket leaked and the water pooled into the cylinder and rusted into the liner. It's about the width of a finger and the length of 2 knuckles ( very technical I know ). The piston is rusted in the matching place and there is a leak mark on the cylinder head between the cylinder and the water channel. So it's on the borderline. Is it mostly likely a leaky gasket and I can let the piston rings smooth it out a bit ? or not risk it and go for another block ? Mental note spray WD40 into unknown engines that are going to stand a while. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted April 22, 2007 Share Posted April 22, 2007 You should at the very least dress it our with fine wet/dry paper and oil to lubrictae it. Be very careful not to let any of the abrasive particles stay in the bore. Letting the piston ring do this is a bad idea - it could break or cause a compression weak spot. Should really bore it out ideally. Les. Quote Link to comment Share on other sites More sharing options...
mad_pete Posted April 24, 2007 Author Share Posted April 24, 2007 How much bore can you get away with on a 3.9 ? vvvvvvvvv Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted April 25, 2007 Share Posted April 25, 2007 If the bore is marked by rust pitting then the only real answer is a rebore, unless bore honing can clean up the area so that it is no longer visible , but still staying within the bore tolerance. The largest amount of bore wear you can tolerate on most V8’s is 3 thou oval…….. the 3.9 is OK for a 20 thou rebore, mine is being machined right now. Don’t forget to send your block to the machine shop with the main bearing caps bolted in to the correct torque as this provides extra ‘stiffness’ to the block during machining and avoid any distortion problems. If the bores are worn, then also the crank will be worn. Like the bores, the crank tends to wear slightly Oval, and 2 thou is considered to be the max. The cranks can be ground up to -30thou in 10 thou steps, however, oversize bearings at more than +10 thou are proportionately more expensive. Also don’t forget to get the heads skimmed to ensure that they are completely flat. If you are using composite gaskets on a pre 94 engine, then you can have 20 thou planed off the heads to allow for the extra gasket thickness. This brings the compression ratio back to 9.35:1 otherwise you loose 0.6:1 giving a compression ratio of 8.75:1, however, this is not normally noticeable. To raise the compression ratio further you can have 20 thou removed from the block face, and a further 10 thou from the heads but then you will need to check and set the preload of the hydraulic lifters and you may also need the inlet manifold planed to ensure a correct fit. If you go down the road of a complete rebuild with a rebore and crank grind then don’t underestimate the cost……………… to do the job properly you are looking at the thick end of £1K…………… Ian Quote Link to comment Share on other sites More sharing options...
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