Sparky_Spit Posted July 30, 2020 Report Share Posted July 30, 2020 I can't find a figure for the depth of the fire ring recesses in the bore tops on a 1500 FM engine. I seem to remember it being 40 thou, but mine measure between 28 and 31 thou so I doubt that is correct. Anybody know for certain what it should be please? Link to comment Share on other sites More sharing options...
Nigel Clark Posted July 30, 2020 Report Share Posted July 30, 2020 I've measured the fire ring recesses on my TR6 block recently at 29-30 thou, so very similar to your figure. The head gasket on this engine is sealing properly. It seems likely Triumph would have used the same recess depth on both 4 and 6 cylinder blocks, so I guess yours is okay. Probably not critical to the last thousandth of an inch. Nigel Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 31, 2020 Report Share Posted July 31, 2020 i would guess the thickness of the gasket varies more by supplier than the depth tolerance of the support recess as the block been decked at some time???, what makes you feel is incorrect ???? in all the years on here its never been raised as an issue , where as gaskets certainly have Pete Link to comment Share on other sites More sharing options...
Sparky_Spit Posted July 31, 2020 Author Report Share Posted July 31, 2020 Nigel - thanks for that, it confirms that my memory is not correct and it must be 30thou, and I'm happy now. Pete - I'm pretty sure the block has not been decked and I only wanted to check the depth as I wrongly thought it should be 40thou. The gasket that came off (Payen) was fine and, out of interest only, its fire rings measured 66thou. Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 31, 2020 Report Share Posted July 31, 2020 all is good then memory is a wonderful thing.................. if it works Ha! pete Link to comment Share on other sites More sharing options...
Sparky_Spit Posted July 31, 2020 Author Report Share Posted July 31, 2020 I normally write down things like this. Then lose it or forget where I wrote it.... Link to comment Share on other sites More sharing options...
Nick Jones Posted July 31, 2020 Report Share Posted July 31, 2020 You’re not still fighting this engine are you Mike? Nick Link to comment Share on other sites More sharing options...
Sparky_Spit Posted July 31, 2020 Author Report Share Posted July 31, 2020 3 hours ago, Nick Jones said: You’re not still fighting this engine are you Mike? Nick Hi Nick - yes, I've run out of excuses. The original FD engine that I quickly put in prior to the 10CR is still doing fine, but I really want to get the 1500 sorted and back in the car. Hopefully the crank will be reground in a couple of weeks, assuming no local lockdown restrictions are imposed, and I'm starting to clean up the rest of the engine and it's components. Fingers crossed... Link to comment Share on other sites More sharing options...
Nick Jones Posted August 1, 2020 Report Share Posted August 1, 2020 That’s ok then, was worried you’d had another failure..... but I guess opportunities have been limited somewhat! Nick Link to comment Share on other sites More sharing options...
dannyb Posted August 2, 2020 Report Share Posted August 2, 2020 My 1500 spit engine has probably been decked a couple of times, but because the the bores are +30 the pistons hit the fire rings, so I had to get the piston heads chamfered. Danny Link to comment Share on other sites More sharing options...
Sparky_Spit Posted August 2, 2020 Author Report Share Posted August 2, 2020 That's interesting Danny; something I'd never considered before. This engine now has +40 Hepolites and they protrude 10 thou up into the fire rings, but without any obvious contact. There is a very slight 45deg chamfer on the piston tops and no witness marks on the pistons nor gasket, but I will check properly with it all dry assembled. If I've any doubt I'll pop them in the lathe and increase the chamfer a bit and re-check. Thanks for the info. Link to comment Share on other sites More sharing options...
dannyb Posted August 3, 2020 Report Share Posted August 3, 2020 I only needed a small chamfer to clear mine so if yours is already chamfered you should be ok. It wasn't until I drove the car that I had the noise of the pistons hitting the fire ring. There was an article I read somewhere online where a 1500 engine rebuild had the same results. Could have been Canleys or some other Triumph specialist. So I had to strip the engine back down and could clearly see where the fire ring was damaged. Also where the engine was decked I suppose the fire ring was more compressed and was spread into the bores. Danny Link to comment Share on other sites More sharing options...
Nick Jones Posted August 3, 2020 Report Share Posted August 3, 2020 Another thing to bear in mind..... According to Chris Witor (among others) there is an issue with current production Payen head gaskets for recessed blocks on the 6 cylinder Triumphs (AK280 iirc). This is something to do with the way the circular fire rings are formed and they are now incorrect often leading to rapid failure. I have also seen a number of threads on various forums where people have had very early failures on recessed-block 4 cylinder engines with Payen gaskets. Hopefully this is not an indication of the same problem....... Not directly related but no 1 son suffered HGF on his 1300 Spit last week (your old engine Mike). This is a flat block engine. The surprise was that it made it home without incident from a fairly long and spirited run then died on the drive at the next cold start. Better than the flatbed of shame..... Nick Link to comment Share on other sites More sharing options...
NonMember Posted August 3, 2020 Report Share Posted August 3, 2020 I once drove my Vitesse from Brighton to Cambridge with a gasket failure like that. It wasn't happy and I'm not sure a Spitfire would have coped on only two cylinders. Link to comment Share on other sites More sharing options...
Nick Jones Posted August 3, 2020 Report Share Posted August 3, 2020 It did still move...... but only just. Sounded bad. Two cylinders only. 3 & 4 both recorded 0 psi on compression testing with violent chuffing noises from the adjacent plug hole. I do remember changing 2 or 3 mk 1, 6 cylinder head gaskets that failed in the same way when worked for a Kingston Triumph specialist in the 80s. All between 5 & 6. Nick Link to comment Share on other sites More sharing options...
Sparky_Spit Posted August 3, 2020 Author Report Share Posted August 3, 2020 Sorry to hear that Nick, but glad it got home under its own steam... possibly quite literally? I've got a bit of a hang-up about head gaskets, I've had 3 go in the last 5 years or so (one on the FD and two on the FM, including the one which ate into the jigging void close to the fire ring and which I subsequently plugged) and I've even changed torque wrenches as a result in case it is out of calibration. So I'm being ultra careful with this rebuild. Checking today, using your info Danny, the +40 Hepolite pistons are nicely made and fit perfectly up into the gasket's fire rings with the chamfer being just the right size to miss them with about 10thou to spare. Feeler gauges, straight-edge, digital vernier and tiny slivers of Blu-tack worked well. When the crank goes in for regrind I'll get the machine shop to also check the head and block faces properly with a professional straight-edge and consider the smallest of skims if needed. Link to comment Share on other sites More sharing options...
Nick Jones Posted August 3, 2020 Report Share Posted August 3, 2020 4 hours ago, Sparky_Spit said: glad it got home under its own steam... possibly quite literally? No steam. The cooling system was unaffected as the gasket failure was only between the cylinders - the rest was fine though the area between 1 & 2 did look as though it had seen some heat. The strange thing was that it drove in apparently in full health on the Sunday evening, only to fail within seconds after cold starting at next use the following Tuesday. Good luck with your build! Link to comment Share on other sites More sharing options...
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