Onan MCCK

[67hat34c]

Are the head bolts wet or dry? Do i Need to use thread sealer and what kind?

Pulled heads due to probable gasket issue. I bead blasted them , painted and cleand up bolts and now going to re install.

 

[TedZ]

On the MDJE i rebuilt they were dry. You must lubricate cap screws you are going to torque...grease is the usual. Maybe diesel guys know something better.

Ted

 

[67hat34c]

MCCK is gas, Has flat heads. Bolts are a 3/8 -20 standard hex head with a thick washer, washer is about 3/16 thick. Was planning on dry install for the washer and bolt head. But considering thread sealer going into the block.

I believe it is dry but want to make sure. Could be possible some are dry and some are wet, not much info out there on this type of repair. Well Guess thread sealer is not going to hurt anything either way.

 

[yachtsmanbill]

Wire wheel the bolts and use a bottom tap in the block (on all bolts!!) Use never sieze on all bolts for re-assembly. You'll be glad you did (or the next owner!). I always clean tap stuff with a 3/8 cordless drill. Just dont cross thread the stuff. ws

 

[67hat34c]

Scott pointed out that most engine bolts need to be oiled, wet torque. This is something I have never done. Anyhow I did find a page in the Onan book that discussed a few torque specs such as the head and sure enough separate paragraph says the specs are made with using engine oil on the threads.

I did clean up the bolts on bench grinder, wire wheel, ospho washed then painted the bolt heads. Scott is bringing his tap set to marina today so we will re tap the holes. Not enough room for cordless drill so will do by hand. Bold holes already cleaned with brake parts cleaner so will have to blow them out again after running the tap.

 

[Boatsb]

I am not sure of the terminology but I was taught to always lube a bolt before torquing it. I use assembly lube or anti seize for wet applications where water can get to it. I have also used pipe dope for places where I wanted to prevent water leakage but that's another story.

I will grab the taps. Do you think you need anything else?

 

[Trojan]

You never put anything on a thread before torquing unless it so states in the build specs. Which are very few. In most applications adding a lube of any type will double the clamp force breaking the bolt. Not good. You could use a sealer on the bolt shank, but nothing on the thread. To clean the threads grind a small flat on the side of a bolt and run it in the holes. Never use a tap on head bolts. Not knowing the class thread in use you could make the threads over size, a loose fit and that could be a real disaster. Use no lube. Head bolts are held to a special class fit. Standard bolts use a more relaxed fit. Most head bolts are special material and hardness.

BILL

 

[TedZ]

http://www.crankshaftcoalition.com/wiki/How_to_torque_a_bolt

Ted

 

[stormchaser]

Aren't most head bolts stretch-bolts, as in use once only?

 

[Trojan]

All bolts are held tight by stretching. How much depends on the bolt size and application. Rod bolts you can measure there tightness with a micrometer. You do not need to loosen a bolt in order to re torque it. Unless otherwise stated you never lube a bolt or nut when torquing. Lacking the ability to measure most bolt stretch. You must rely on the torque to stretch it. Using special load cells and testing the stretch length when torqued is applied, is the standard way of setting the torque speck for a given application of the fastener. The instructions that Ted referred to is not entirely correct. I worked as a torque application engineer at the time the feds came in and required every nut and bolt at Jeep to be torqued. There were three types of fasteners. Safety torques mandated by the feds. Then application torques like nuts and bolts that had to be tight, but if loose was not a safety issue and then just general torque. Most head bolts can be reused. The ones that can't be are the ones where the torque is up almost to the yield point and re-torquing will stretch the bolt beyond the yield. There are not many like that. Some of the self threading bolts or the triangle threaded bolts can not be reused. Like Seat belt bolts. Some special head bolts can not be reused, but there aren't many one time applications.

BILL

 

[Maynard Rupp]

All true Bill. Just clean, install, and torque the bolts. These stupid little engines are about as sophisticated as an older Briggs and Stranton. Don't over think this thing folks. Just clean the bolts, install the head and gasket and torque them down. Ours shows 150 pounds compression on each side. Don't forget, this stupid engine doesn't even have a distributor and both cylinders fire at the same time. How much more basic can an engine get?. I torque my genny's head bolts with a box wrench. I also have a hard time believing that he blew a head gasket unless, of course, he liquid locked the engine by pouring crap down the poor little carburator. It did take me a whole day to adjust all those linkages and springs to get the thing to run at the correct voltage outputs under varying loads. That is a tough job with a carburated engine, but it can be done. Ours performs perfectly now.

 

[Beckytek]

Maynard, how do you time those things? With the way the plug wires are enclosed for spark suppression I can't connect my timing light anywhere. I was also wondering which plug to connect to, but since you said they both fire at the same time it doesn't matter. Thanks for clearing that up. I don't know what I'd do without all your expertise. Ron

 

[Maynard Rupp]

Maynard, how do you time those things? With the way the plug wires are enclosed for spark suppression I can't connect my timing light anywhere. I was also wondering which plug to connect to, but since you said they both fire at the same time it doesn't matter. Thanks for clearing that up. I don't know what I'd do without all your expertise. Ron

Just set the point gap and forget it. That will affect your timing, but, as you say, the shielded plug wires prevent the use of a common timing light. You can use an ohm meter on the points, rotate the engine slowly, and when the points break, stop. Now look at the timing mark on the flywheel. It should point to the timing value in the book. There is no advance mechanism. That is how we time small airplane engines and fuel dragsters. This engine sure ain't as fancy as either of those.

 

[Beckytek]

Thanks Maynard, that sounds almost too easy. I was pulling my hair out trying to figure that one. I've been fooling around with this generator for 4 years now and it runs very good but I like to make sure everything is in spec. This was the last thing left to do. Ron