[Tom Mobley]

Hi,

I want to rebuild a Briggs 3 HP lawn mower engine with my 10 year old son. I have lots of experience with car engines but can't remember ever doing one of these.

Do I have the crank ground, cylinder bored, new OS piston and rings, all that or does anybody even do this stuff anymore?

Anybody up on this stuff?

 

[Rod]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

In the high school mechanics class I teach we start with a single piston Briggs and tear them down and put them back together and hopefully they run. Small engine repair shops have all the parts and manuals. There are many different generations of these motors so getting the model number is a good place to start. It is usually stamped on the shield. The only specialty tool that makes things easier is the flywheel holder that lets you take off the nut without the motor turning over. (had a student try and take the flywheel off without taking the nut off first.........it came off alright, in 3 pieces and a loud bang) Other then that just the usual engine building guidelines like following torque specs and replacing gaskets. If I can I try and leave the carb area as one piece just to avoid messing with the spring and small parts. Most people just toss these motors and buy new due to the low prices but they are a fun little project and a good place to start with kids.

 

[68KMENO]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

lets see where to start ..... its cheaper to buy a new motor

BUT ...

the the main bearing surface in the block will more then likely be ob longed as its just cast aluminum that means you've got to have the tool to remachine it an then install the bushing that repairs it ... if the bore is not real bad you can just install new rings ... most of the time NOT possible ..the valve's & seats are no problem just your standard grind & lap ... except you grind the valve stems to set the lash when your ready ....

couple of questions for ya .... does it run now ??
pull the pull start cover off the flywheel & grab it an try to move it up an down .. if you feel play .. the block needs bushed !!
if it smokes the bore is gone !!
yes all the parts are available but .... $$$$$$
if it runs NOW ... just take it apart clean the carbon out
install one of the new replacement pointless ignitions retro fits ..as it makes it possible to run the ob longed case till its wasted !! (the timing depends on no slop in the case ) BUT ... the electronic Ing is much less picky ... is cheap insurance
an let your son do then work ...
there's nothing in there he can hurt
good luck .... but most of all :thumbsup: for the son's first Project

 

[JWagner]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

Generally, these were considered throwaway motors. However, they can last a long time if the oil is changed. To rebuild one, usually you just put new rings in and new oil seals. Most of these have a bare aluminum bore which , oddly enough, works quite well. The aluminum traps grit from the oil and acts like an abrasive that wears the rings out. The piston is hard chrome plated and is probably not available in an oversize. The bearing hold up pretty well if the oil does not run very low, so that should not be a concern. I am doing a similar project with my GF on a 1960's B&S motor. I used to work in a small engine shop in the 60's , so I am pretty familiar with these old motors.

 

[david_396]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

I am doing a similar project with my GF on a 1960's B&S motor. I used to work in a small engine shop in the 60's , so I am pretty familiar with these old motors.

The girlfriend sounds like a keeper.

 

[Tom Mobley]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

the engine ran summer before last. Funny thing is it started good and ran good but had very little power. The rubber T handle broke off the starter rope and I discovered I could pull it just fine without it, just grabbing the little knot on the rope. Seems the compression is a little low. I don't hear any knocking or other nasty sounding noises, maybe I'll skip the crank grinding.

 

[smittyocat]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

Tom,
you can buy a book on these like a haynes manual that goes through step by step repairs and overhaul. I did the same thing with my son. I went own to the local mower shop and got all the parts. It was a fun project.

 

[Tom Mobley]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

looked around on the net a little, found rebuild kits for $50. I can work something out if the case is damaged. Actually that might be a good thing for my son to see, how to fix something like that.

 

[69boo307]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

The engine on my Toro got hydrolocked after sitting out in a thunderstorm. Literally rusty water was coming out of the spark plug hole. I didn't realize this until I cranked it and crud starting shooting out of the muffler. It was amazing that it even cranked.

I rebuilt it for about $50. Bought an engine gasket kit and new rings, honed the cylinder and cleaned everything up, put it back together. It really wasn't hard at all, if you've ever rebuilt a car engine it's definintely a piece of cake. So far so good, if I get another season or two out of it I'll consider it money and time well spent vs. buying a new one.

 

[planeoldguy]

Re: anybody here know about rebuilding small engines? Like B&S 3HP?

You can get oversized pistons for them, but be careful, the overbores tend to run hotter. I will do overbores on snowblowers, but not lawnmowers.

If the rod bearing is wiped out you can get an undersized rod and cap from Briggs and have the crank ground to size. The machine work is fairly cheap, I think I paid $70 for my last cyl overbore and crank grind.

There are many good books available over the net regarding small engine repair and rebuilding.