I guess its Halloween, did not mean to scare you
RV7AAAAAAA said:
gmcjetpilot said:
Also tools are no big deal, but don't use an el-cheap-o un-calibrated torque wrench for example.
This is a perfect example of what scares me about building my own a/c engine. I read somewhere (maybe Mattitucks site). That you don't just torque the rod bolts but measure the actual stretch of the bolt itself. I've been a backyard mechanic for a long time on cars and never heard of such a thing. I've done a pretty good job as a kid in the past putting junk yard parts together in an automobile and going 1000's of miles with no problems. But I'm very humbled by the whole RV glider thing.
My RV 8 buddy tells me I'm getting too much info. But here I go rebuilding my own 0-320 with help of course, ready or not.
Jim
7A - loving this thread and anything about Lyc. engines
I hear you and it was not my intent to scare you, but I know what you mean. I felt the same way, oh my gosh what secret is there?
I'm not sure what your saying about measuring the bolt stretch. I know what preload is and yes the bolt does stretch a fixed amount, and yes you could measure it. They skyranch book will address this if it has merit, but I don't recall. Get the book.
Yes PRE LOAD or bolt stretch is critical. This gives the bolts fatigue life. However torque (as far as I recall) is an acceptable (and most common) method to get the right stretch. The "SNAP" type torque wrench may not be suitable for the torque and hold method.
The OH manual explains all limits and everything you need to know about assembly. If there is a "stretch" spec it is there. If it is not and only a torque limit is given, that is what you need to know. I'm just saying an old rusty torque wrench that has not been calibrated is a no no.
I assure you its NOT a big deal to get proper "stretch". It's very simple to tighten (torque) a nut on a bolt. The main players are the tool, thread lube and technique.
Measuring the stretch is required for some designs but not the 320/360/540 as far as I recall. That method has advantages. I only built one Lyc, (O360) with some good help and that was a few years ago. It may be a good double check, but if it is not in the Lyc OH manual or skyranch manual, it's not a must.
I do remember off the top of my head the Skyranch book recommends holding the torque (30 seconds). Meaning when going to the final torque value, go slow in one motion and hold it there for a period of time, just don't let it go when you hear the beep (audio/light torque wrenches are cool BTW). I have to re-read the book to get the details. Skyranch has a section just on Lyc rods. There are also Lyc service letters / bulletins that address assembly.
The rod bolt's are probably the most critical, followed by the case bolts, than cylinder base bolts. They need care and attention. Bottom line, its just a NUT to tighten. Ths stuff is farm tractor technology, not the space shuttle heat tile's.
The Skyranch book talks about common errors and gotchas made during engine assembly and how to avoid. Some of the mistakes are made by the manufacture! I guess they where Monday engines.
That reminds me, with the level of attention you will give your own hands on rebuild, even if inexperienced, you're likely to do a good job. Someone torquing a 100 bolts a day, everyday, statistically may make a mistake at some point. Just something to think about. Care and attention, coupled with knowledge goes along way in overcoming lack of experience. You are going to sweat over every bolt and do a proper job of it.
Truth be told there are probably many engines with improper bolt torques that fly to TBO. It's just a matter of fatigue limits and margins. The PRE LOAD or stretch is a GOOD GOOD thing for bolt fatigue. Even improper torque may not cause catastrophic failure, but you will loose your margin. Think about the bolts, crank and rods, they look like steel work for a bridge. Also this is the reason rod bolts are not reused. They are trashed during OH. Even after being torqued once, you may need to trash them. You burnished the threads and subsequent re-torquing might be off.
You really have try to NOT to follow procedures to blow it. These engines where made to be field repairable by A&P's.
Here is a Halloween story to scare you. Bolt torque (bolt stretch) is very dependant on thread lubricant. There was a case, I believe Continental, where someone at the factory decided to switched thread lube without telling anyone. It caused the bolt pre-torque (stretch) to go wacky, causing real problems. This was the manufacture! Again NO BIG DEAL, Lycoming specifies the proper thread lube. It's not motor oil. Also you keep the thread clean and dry and unpainted until ready to lube and install. You can not have paint on the cylinder base and base studs. The info is there, just follow it. Get the OH manual, a genuine one goes for about $50 I think. I see them for $20 sometimes on eBay. Not sure if they are copies. The one I have is in a three ring binder and has glossy print pages.
KNOWLEGE is power. Engine tear down and build up is not harder than riveting. No rocket scientest credentials are needed. Like riveting you will need some special tools, but if you have hairy knuckles that drag on the floor when you walk, you're well suited to torque a nut.
(mechanic joke). Seriously a trained eye is good for all phases of a rebuild, tear down, inspection and assembly, but its all explained in the manual. Again its not a bad idea to have someone help, a second set of eyes, but take the time to read the references.
Even if you don't ever rebuild an engine, I recommend the
Sky ranch manual. It is technical, but it's so well written anyone can understand it and get a lot out of it, including operations, performance, maintenance and trouble shooting. Even if you get someone to rebuild the engine for you, this book should still be required reading. You'll have lots of questions to ask your potential re-builders to determine what they're going to doing and how. You may be surprised how little some engine builders know. Mattituck DOES know what they're doing. If you don't want the joy of building your engine, send it to Mattituck, can't go wrong. Clearly a pro rebuild has advantages, not the least of which is warranty.
Take a deep breath, get the Skyranch engineering manual for sure and a Lyc OH manual and read them. The Lyc overhaul manual is dry and just the bare min text, step by step, data and limits, but it has tons of info. You can't overhaul an engine without it. Even if you decide not to rebuild your own engine, the manuals and worth having.
You're not rebuilding for convenience; you're rebuilding your engine to learn. You will just happen to save money, but that's just the frosting on the cake. Plus it give you an excuse to buy more tools.
