Our Customer's Yanmar Kept Blowing Head Gaskets

today we have a real quick video on a small job we took on doing some machine work on this three-cylinder Yanmar specifically a 3tnv 84. our customer brought us the short block in the cylinder head After experiencing overheating of the engine and a blown head gasket after at least one attempt of replacing the head gasket and seeing a failure in the same spot on the center cylinder they determined that the deck of the block needed to be resurfaced with some layout fluid on the deck surface the block was fixtured on our boring and surfacing Mill and a beginning cut of one thousandth of an inch was started for reference for those of you who don't typically work in Dimensions that small one thousandth of an inch is roughly one-third of the diameter of the average human hair with the initial one thou cut it's obvious that our cutter did not touch the entire surface of the deck from our point of view the cutter cleaned most of the right Edge all of the front edge and most of the left Edge as well as near the head bolts on the back side if this had been a five thou cut and it looked this way I would be very concerned that we weren't set up true but in this case it can be attributed to a combination of warpage from overheating as well as a slight difference between my setup and the last time this block was decked by two thou total off the deck we see that the cutter touched the entire deck surface excluding the areas where the head gasket seals especially around the center cylinder the low spots around the cylinder definitely would contribute to a head gasket failure at three and a half thou the surface is starting to look better but still not perfect with one more cut and a total of about four thousandths of an inch off the deck surface of this block we're confident that we will have a flat surface and a nice surface finish to give a head gasket the best odds of sealant we're planning on honing the cylinders of this block but while it's set up on the machine I went ahead and machined a bit of a chamfer to take off the sharp top edge of the cylinders to Aid in installing the piston rings later on after overheating multiple times the cylinder walls and the Pistons had a small amount of scuffing so after discussing with the customer we opted to get a set of 0.25 millimeter oversized pistons for the rebuild which puts our minimum final board size at 3.3169 inches when we do the conversion since our micrometers and bore gauges read in inch sizes since we have just shy of 10 thousandths of an inch to take out in the cylinder home we'll start with our coarse Diamond roughing Stones which are great for removing larger amounts of material very quickly real quick I want to say thank you to all of our fans if you're new here be sure to hit that subscribe button and maybe even head over to our website and cop a sticker after just a couple of light Strokes in the home we can see the areas at the top of the cylinder which are either worn larger and or warped where the hone hasn't touched yet our goal after honing the cylinders will be to have cylinders that are on size with a consistent surface finish for the entire cylinder top to bottom when you're only going ten thousandths over size or less it's kind of a toss-up between boring the cylinders and then honing or simply using the hone like this to remove all of the material if you're going to go any more than ten thousandths oversized it's more efficient to bore the cylinders to within three to five thousands of finished size before moving into the home well I'm sure this looks simple from your living room couch I can assure you that the cylinder hone is one of the more complicated machines in the Machine Shop to master all of your work has led up to this point and you generally have a very small amount of material to work with to make sure that you hit your tolerance for proper piston to wall clearance make sure that the cylinders are round and straight from top to bottom and that doesn't even begin to mention getting the proper surface finish for proper ring Sealing after all the cylinders are roughed out we're going to start the process of finishing out the cylinders beginning with our coarse Stone abrasive which you can see leaves a slightly smoother surface here on the center cylinder compared with the diamond on the outer cylinders the rough Stone is used to bring the cylinders out very near to final size before a stone with a much finer grit is used to finish our cylinders to the proper diameter with all the cylinders finished this little block should be good to go for another life cycle so we're going to get it completely cleaned up and ready for assembly as we all should know when your engine is overheated and blown a head gasket you're really only fixing half of the issue if you only surface either the head or the deck of the block this head also had some issues with the valve ceiling so be touching up the seats but before that we'll be resurfacing the head to help negate any future head gasket issues sure enough the surface of this head closely mirrored the surface of the engine block and in fact it actually ended up being almost twice as bad as the block requiring seven thousandths of an inch to fully achieve a flat surface this no doubt attributed to the head gasket issues the valve guides were actually in decent shape and we opted to get new valves for the engine and touch up the old valve seats here on the valve seat machine while worn the seats didn't look bad enough to Warrant the X-ray expense of being replaced as long as we can cut the seats to get a good Centric and aligned seating face while still remaining within the specified limits of valve depth relative to the surface of the head will be in good shape as usual our goal is to remove as little material as possible while still producing a quality seat with all the intake seats cut we can check our valve recession with our new valves to verify that they're all within the allowable spec of twelve thousands to twenty thousands below the surface of the head they are leaning towards the Lower Side of the specification which on a diesel like this means a lower compression ratio but we have also raised to the compression by surfacing the block so we're comfortable being in this position the exhaust seats are resurfaced as well and I know it's difficult to tell on the video but the exhaust seats machine differently to the intake seats since they're made of a notably harder material to withstand the hotter temperatures that the exhaust valve experiences the exhaust valve recession spec is the same 12 to 20 thousands below and we came in on the deeper side of spec just like the intake seats while it's always easier to produce a high quality end product when you're replacing every single part of the engine it's not always necessary and it becomes a balance of cost time and quality in this case the increased cost and labor time of replacing the seats would only be marginally beneficial as our end result is still within the specified tolerance but in the end we've tackled the critical areas of the engine to have good ceiling valves good ceiling piston rings and Solid Surfaces for a good ceiling head gasket the core reason the engine was here in the first place thank you all for watching and we hope you enjoyed this quick video stay tuned for some of the Cool Jobs coming up including continued work on the Ford Model A and the 4.2 liter Jaguar thanks for watching and we'll see you in the next one

Channel: Jim's Automotive Machine Shop, Inc.

Views: 512,901

Keywords: Engines, Engine Machine Shop, Machine Shop, Engine Shop, Machining, Automotive Machine Shop, Automotive, Cars, Trucks, Tractors, Gas, Diesel, Performance, rebuild, high performance, internal combustion engine, pistons, cylinder heads, jim’s, jim's automotive, jamsi, jamsi online, Blueprinting, rebuilding, engine building, connecting rods, engine block, boring, valve job, engine rebuilding, jim's automotive machine shop, small engine, 3 cylinder, yanmar, turbo diesel, head gasket, blown

Id: QndrzRoDWvY

Length: 6min 15sec (375 seconds)

Published: Sun Nov 13 2022