ChrisV Posted October 20, 2018 Report Share Posted October 20, 2018 I see a handful of aircraft listings stating that a plane has been ~700 SMOH and 50 STOH. Should I be concerned that there was a top overhaul done 5-600 hours after a major overhaul? Quote Link to comment Share on other sites More sharing options...
81X Posted October 20, 2018 Report Share Posted October 20, 2018 Depends on the engine type. It could range from manufacturers issues to ADs to operator error to mechanic error to premature replacement error. Do you have more information? Quote Link to comment Share on other sites More sharing options...
StevenL757 Posted October 20, 2018 Report Share Posted October 20, 2018 Agree. More details would help. Quote Link to comment Share on other sites More sharing options...
ChrisV Posted October 20, 2018 Author Report Share Posted October 20, 2018 Here is an example(not the one I was looking for): 1984 231K Turbo, 2874 TT, 1066 SMOH 304 STOH. Not sure which engine it has. Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted October 20, 2018 Report Share Posted October 20, 2018 7 minutes ago, ChrisV said: Here is an example(not the one I was looking for): 1984 231K Turbo, 2874 TT, 1066 SMOH 304 STOH. Not sure which engine it has. Continental TSIO-360-LB which has a TBO of 1800 hours Many of the 231's needed top overhauls at mid time since they were flown too hot. I bought an '83 in 1993 with 1000 since new and it needed a top end overhaul. Thankfully the seller agreed to do it. Back when these airplanes came out, graphic engine monitors were just being talked about for single engine GA airplanes, but few people made the investment. The factory CHT only showed the temp on one cylinder so it was easy to cook the cylinders. Quote Link to comment Share on other sites More sharing options...
larryb Posted October 20, 2018 Report Share Posted October 20, 2018 It is not just planes without engine monitors. Most of the Acclaim listings show cylinder replacement on young engines. 1 Quote Link to comment Share on other sites More sharing options...
bradp Posted October 20, 2018 Report Share Posted October 20, 2018 It's just as much how the engine operator behaves with regard to management, temperatures, preventative maintenance, frequency of use, etc. Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted October 20, 2018 Report Share Posted October 20, 2018 1 hour ago, larryb said: It is not just planes without engine monitors. Most of the Acclaim listings show cylinder replacement on young engines. Mooney's marketing is much to blame for top end overhauls. Everyone wants to go fast but if they would balance fast with being reasonable about power settings and engine management owners would be happier in the long run. Getting there 10-15 minutes sooner is fun, buying six new cylinders not nearly as fun. 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 20, 2018 Report Share Posted October 20, 2018 It all depends... A pilot can decide to really conserve the hardware by watching how he operates the plane... or... A pilot can decide that outright speed is the most important part of his flying... Speed and turbos go hand in hand... high altitudes and speed go together... low density air is good for speed, but crummy for cooling CHTs... Well operated turbos can expect a TOH around the halfway point... not a terrible price to pay for the greatness of flying fast in the FLs... the long climb can take a toll as well... On a more conservative note... a NA engine, flown around 10k’, LOP can go the distance... There is plenty of guidance on CHT control and what works... and the instruments to do it... It is pretty easy to ruin a set of cylinders before their time... So always be on the look out for equipment status when purchasing a plane... Trust but verify... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Yetti Posted October 20, 2018 Report Share Posted October 20, 2018 For the 231... http://www.mooneypilots.com/mapalog/M20K231 Eval Files/M20K231_Eval.htm Quote Link to comment Share on other sites More sharing options...
ChrisV Posted October 20, 2018 Author Report Share Posted October 20, 2018 That is a great article. Thanks Yetti! Quote Link to comment Share on other sites More sharing options...
Cruiser Posted October 20, 2018 Report Share Posted October 20, 2018 There are two primary reasons for a top overhaul. 1. burned exhaust valves 2. excess oil consumption There are others but these are the main reasons. Recently Mooney issued a.service bulletin on the Air-Oil separator because excess oil consumption was blamed on cylinders when in fact it was crankcase pressure forcing the oil out. So, how do we recognize and prevent premature top overhauls? Truthfully, I don't know. There are some things that make sense. Temperature is evil in an airplane engine. The higher the temperature the quicker the damage. Even though valves are mainly a function of tolerance and fit, the lack of that precision is what wears them out. doing it at higher temperature will wear them out quicker than doing it at lower temperature. Turbo charged engines run hot(ter) then NA engines. It follows that the turbo have more heat related issues than the NA group. With the LOP revolution new guidelines for temperature limits have been generally accepted to be around 380°F CHT in cruise. This is supposed to extend the life of the cylinders and protect the valves. I have no data to support or refute this claim. It does make sense but there are still failed valves even in LOP run engines. So? On the other hand, ROP run engines have a checkered history of some making TBO and some not. (Top overhauls) Where is the common thread that links all these failures? It makes sense that EGT must play a part. Even if the exhaust valve (cylinder) was going to fail from poor fit due to poor machining it is accelerated or delayed by the heat environment it operates in.Need more proof? Why do we not see an equal amount of intake valve failures from poor machining (fit) ? What is different ? HEAT? Correct me where I am wrong. I welcome the insight. Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted October 20, 2018 Report Share Posted October 20, 2018 According to Mike Busch, top overhauls are also a breeding ground for maintenance-induced failures, so I'd be cautious about an engine that had a very recent top overhaul (maybe less than 100 hours?) 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 21, 2018 Report Share Posted October 21, 2018 Exhaust valves have little tolerance for poor machining.... Or blocked oil flow passages in their guides... Compared to intake valves that are surrounded by a mixture that is less than the OAT... If you were a valve... would you rather be in... - filtered air, chilled with evaporating fuel, semi lubricated by all that LL stuff... or - a Heated burning plasma of high oxidative properties, surrounded by the ash and carbon deposits of days gone by... usually it is the exhaust valves that go awry... the oil they are cooled and lubricated by, bakes in the excess heat on shut down... the oil flow gets blocked by carbon/coal in the shape of the guides themselves... That single CHT gauge with a red line of 450° has not really been very helpful to the actual longevity of engines... Cooling valve guides prior to shutdown is a similar discussion to cooling turbos prior to shutdown... lots of oil flow gets used to cool these very hot spots... There are good ways that are not really obvious without really good instrumentation... and discussions like this... PP thoughts only not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Sime Posted October 21, 2018 Report Share Posted October 21, 2018 (edited) I purchased my '76 M20F in December last year. At the pre-buy, my mechanic noticed that the engine was using a lot of oil...around 1 quart per hour of flight time. The current owner at the time strongly believed this to be 'within spec/tolerance'. We felt otherwise, but we were butting heads and he wouldn't lower the price on the aircraft. I would have liked to get another $3K off towards the cost of the overhaul that we knew the motor needed. But it was a reasonable overall deal and the aircraft had 4100TT and 950SMOH. Prop had very low time on it. At the annual in Feb this year, we decided to go ahead with the top end field overhaul. Upon tear down, two pistons looked average with edge wear on the crowns so we replaced with new, and rings/seals on all four cylinders were replaced (along with a hone and cleanup of the heads). Initially, there was expected blow by from 8 quarts to 7 at about the 7 hour mark, and then with more flying, the usage went down to 6.5 quarts. I put another quart in just to be safe. She has done about 25 hours now since the rebuild and has only had two quarts total added (including the initial 'top up' quart. She's currently sitting on 6 quarts so I'm just going to keep flying her and monitor the oil consumption, only adding oil if it continues to drop lower. I cruise at no higher than 380F CHT on #3 which is the hottest cylinder. I cannot say as to why the aircraft was using oil excessively beforehand, but the top overhaul fixed things! Edited October 21, 2018 by Sime Quote Link to comment Share on other sites More sharing options...
Mjknick@gmail.com Posted October 21, 2018 Report Share Posted October 21, 2018 In how many years some have had corrosion issues and need replacement. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.