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Honda G400 10hp Help needed.

Started by Coon, November 25, 2011, 08:47:54 PM

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Coon

I am working on a little bit of a project here and trying to get an engine running.  The engine is a Honda G400 which is 10 hp.  The engine would not start and was showing us signs of no compression so I started to diagnose.  I removed the carb, muffler, recoil, and finally the head.  Upon head removal I discovered that the problem was the valves not seating properly.  The intake valve actually looked pretty good but the exhaust valve was carboned up and not completely closing off.  I pulled the valve out and will be going out to lap both of em later tonight yet.  The cylinder walls look very good for the age of the engine so I will leave the cylinder and such alone for now.  When I removed the head I was cautious as to not bugger up the head gasket if at all possible.  It came off as if it was a new gasket.  Can't find any damage to it anywhere.  I am at a stand still, once I get the valves lapped and installed, due to not being able to find the proper torque specs for the head bolts.

We really need this engine running as it is for a little Ram-rod that we need to use.  Ram-rod you ask?   :D  It's a little stand on bobcat type unit.  There is limited room in the engine compartment and we have searched for a different engine that would fit and has enough horsepower with no luck. 

Brad. 
Norwood Lumbermate 2000 w/Kohler,
Husqvarna, Stihl and, Jonsereds Saws

tapper2

Not entirely uncommon to see a sticking valve. Clean it up, lap it in and it should be good. Not sure if it's an interference engine, but after you lap the valves in, seat the valves then bench test the fit by pouring a liquid in the intake & exhaust ports to ensure the valve isn't bent. If so... the liquid will seep through around the valve. Usually they can be cleaned up and put back together w/out much hassle.
Belsaw m14, 1992 Ford 1720, Homebuilt  bandmill, Franklin 120b & a bunch of worn out, banged up stuff........gotta love it.

sawguy21

That is a valve in block design so piston interference is not an issue. 
100 in/lb on the head bolts should work just fine.
old age and treachery will always overcome youth and enthusiasm

Coon

Thanks for the speedy responces.  I was researching more online and found a table that listed torque specs for honda engines.  The closest info I could find there said 40 ft/lbs.   :o  Yeah uhmmm sure and the donkey milked a turkey at the circus tonight  too eh.   :D
Norwood Lumbermate 2000 w/Kohler,
Husqvarna, Stihl and, Jonsereds Saws

Paper Maker

  One thing I like to do in a situation like this is to take a paper towel or a dollar bill or something similar. Put it over the carb intake. It should suck the paper every time you turn the engine over. On the exhaust it should blow the paper every time you turn the engine over. If the opposite should happen on the intake or exhausts you will have problems with one of the valves seating properly. The valve steam could be gummed up, valve seat damaged, or a bent valve steam. Im sure there may be other causes also. If you already have the valves out you can put it in a drill or drill press turning it slowly using something as a reference point you should be able to tell if its bent or straight. Just make sure you don't over tighten the valve steam in the drill chuck. You certainly don't want to scar the steam. I don't think that Honda uses hydraulic lifters so you may want to look at your tappets. There may be some type of problem there. The only other thing I know of is to check the valve clearance. I'm not sure at all, but it should be close to .006 to .008 clearance. But I doubt this will be your problem. If none of this solves the problem it almost has to be the piston rings. Check the ring gap by carefully removing a compression. Put it in the cylinder and use the piston to square it up in the cylinder wall. It should have less than 30 thousand gap. Any more and it would be considered reject. I'm not an expert by any means but I used to enjoy working on small engines. When find the problem I would like to know what you found. Hope some of this helps.        Marcus   

mad murdock

Proper torque sequence is as important as proper torque. The torque specification is a function of the size of the bolt, the thread pitch and the type of material the threads  in the block are made of. If the block is iron or steel, I would  buy the previously suggested 40 lb/ft if the bolts are say 3/8" or larger(or equivalent metric size maybe 10mm). If the threads in the block are aluminium, I would stick with the lower torque suggested of 100 lb/in. Use An alternating pattern so that the head is torqued evenly and you should be fine. You only need to torque in steps if the head gasket is new, since it crushes when torqued down it is even more important that it is done as evenly S possible. To preclude valve problems in the future, a steady regimen of a splash of Marvel Mystery oil in the gas is invaluable.
Turbosawmill M6 (now M8) Warrior Ultra liteweight, Granberg Alaskan III, lots of saws-gas powered and human powered :D

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