OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk SB Model 45 - Clutch and Engine Problems

We may have a few problems there Stuart. I think the first thing you need to do is to remove the engine from the mower, and see if it is still stiff. If the problem is just an alignment one, the engine may be free to rotate once it is removed from the mower. If it is still tight, it is going to be necessary to remove the crankcase cover again and reassemble the engine step by step. Please do not try to start the engine until we get this resolved.

To align the camshaft and crankshaft correctly you need to align these two circled dots,

Sorry the keyboard had a fit half post there, also I am hoping there is no damage to the crank bearings in the cover from leaving the key in the crankshaft, memory says it should fit past but may not...

The camshaft timing seems to be right by a simple tooth count.

The key may have wounded the crankshaft oil seal as well as the main bearing, plus I don't know what the final status of the crankcase cover gasket will have been after removal and re-installation. Also, if the tappets happen to have been put back into the opposite positions (intake and exhaust interchanged) the tappet clearances may be quite a way out.

I'm not confident yet about whether there is end thrust on the crankshaft due to the clutch cotter pin adjustment, which is why I've asked for the engine to be removed.

Once we work through these points, hopefully all will be well - but I don't yet know the cause of the rotational stiffness, unless it is end thrust on the crankshaft.

Stuart, this may appear to be a stupid question, but why did you disassemble the crank case cover?

In that pic the timing seems out by one tooth would that be enough for a valve to just hit and make it hard to turn over?

The valves cannot hit the cylinder head in that engine due to incorrect timing, Chris, I do not think that is the problem. (It is sometimes very different though, on some OHV or OHC engines, when the valves can hit the piston with devastating results. That is why it is a good idea to replace the rubber cam drive belt in certain car engines at the recommended intervals.) However if the camshaft timing is out by one tooth, the engine would run badly if at all.

Grumpy, I have taken off the cover again and removed the larger of the cogs. The pull cord now moves quite freely so it must be something wrong with the alignment when I place the big cog back in. Your thoughts (and remedy!)

To time it the timing marks should look like this...grumpy will tell you the best way of aligning up the timing marks.In that pick its one tooth out....

Stuart, the first step is to rotate the crankshaft (which has the small gear on it) until the dot on the gear is at the closest point to the camshaft gear. Lift the camshaft gear (the big one) out of mesh with the small gear, and rotate it until the dot on the gear is in line with the dot on the crankshaft gear. Then slide the camshaft gear into mesh with the crankshaft gear so the two dots are close together, as in Chris' drawing. Remember the gears have helical teeth, so the camshaft will rotate as you slide it into place. You choose the right point and slide the gear into place. If the dots are not perfectly aligned, slide it back out, rotate it one tooth, and try again until the dots are matched.

The because the engine is only tight when you have the crankcase cover installed, it appears that installing the cover jams something, probably either the crankshaft or camshaft. Can you post a picture of the black gasket that goes in between the crankcase cover and the crankcase, please. That gasket is 0.015" thick, and the axial clearance of the crankshaft is only 0.008" maximum, so if you have left out the gasket, the crankshaft will be squeezed endways when you tighten up the screws that hold the crankcase cover, and the crankshaft will not be able to rotate freely.

I have replaced the cam shaft gear as described. Still getting stuck when I pull the cord. On closer examination it appears the main source of friction is when the piston is at the top of its stroke. ie when it is furthest from the crankshaft. The gasket was ruined when I took the crankcase cover off, and after some advice from a mower shop, i used sikaflex to take the place of the seal. Where to from here?

Stuart, as I told you previously, the Briggs and Stratton engine relies on the thickness of the crankcase cover gasket to set the end-clearance of the crankshaft. First, you should not have taken the crankcase cover off in the first place - all of your problems since have stemmed from that mistake. Second, it is not unusual for gaskets to be ruined when you dismantle an engine - when it happens, you have to fit new gaskets. Your crankshaft is jammed because of the absence of the gasket which provides its end clearance. Buy a gasket and fit it properly. I suggest you do not ever go back to that mower shop: it appears the person who advised you has probably never dismantled a mower engine, since most of them rely on that gasket to set crankshaft end clearance. There is nothing wrong with him not knowing anything about mower engines, but there is definitely something wrong with him giving stupid advice to a customer when he is consulted as a professional. The people serving at the counter in mower shops usually know nothing about mower engines, but normally they have enough sense to refrain from giving advice on the subject. They have a mechanic in the back room who (hopefully) knows about engines, but his time is worth too much to have him waste it talking to customers.

Thanks Grumpy and wilco. I have cleaned up the surfaces of the engine and cover and will now purchase a gasket. I have fitted the cover back on loosely and the pull cord seems to be working reasonably freely with the only real resistance coming when the piston is at the top of its stroke. I have looked for a gasket on the Outdoorking website but there are so many. What is the exact name of this gasket? The engine is a B&S 3hp model 80202.

To find the part number for the gasket I need the full string of numbers stamped on the cooling air cowl of your engine, right above the muffler. The Model is 80202, but I need the Type to identify which variant it is. The third group of numbers, the Code, will tell us the engine's year, month and day of manufacture.

The gasket's name is Crankcase Gasket. The standard (i.e. 0.015" thickness version) gasket for a generic 80202 is Part Number 270833. There are two thinner versions available, to adjust crankshaft endfloat, but you probably will not be able to buy them in Australia. The correct procedure is to fit a standard gasket and measure the end float with a dial gauge, then either fit a thinner gasket, or add a thin one to the standard one, to achieve the required endfloat of 0.004 - 0.008". However I doubt you have a dial gauge, so for this purpose I suggest you assemble the engine with a standard gasket and feel whether there is endfloat but not much of it, and the crankshaft rotates freely with the spark plug removed from the engine. If so, it will be fine. Incidentally I think you will probably find the resistance to pulling the starter when the piston is close to the top of its stroke will not exist when the spark plug is removed. It is a very bad idea to pull the starter with the spark plug installed and without the crankcase cover installed, since a substantial vertical force is applied by the compression, and the crankshaft is not supported to resist it.

Yes thanks, all resistance gone now I have removed the spark plug. The engine type is a 4016 01 and the code 90021303. Thanks for your patience.

Here is the illustrated parts list for your engine:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6ntABVJ1DajI.pdf

I can confirm that the standard thickness Crankcase Gasket for your particular engine is P/N 270833.

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/flivAJX-nfBhU7y.pdf

Your engine was made on 13 February, 1990. That is long after Rover took over Scott Bonnar in 1980, but if I recall correctly the Scott Bonnar plant continued to operate for some time after the takeover, before Rover moved all production to their own plant. That is a matter for Deejay to clarify.

I think the next step is for you to check the tappet clearances, in case you interchanged the intake and exhaust tappets when you reinstalled them after they fell out when you removed the camshaft. To do this you will need the crankcase cover installed - do not tighten the screws since that would lock up the crankshaft. You must have the cover installed though, because it supports one end of the camshaft, and the camshaft has to be supported for the valve clearances to be correct. Look at this illustration from the parts list:

The red oval shows you where the valve cover/breather attaches to the engine, directly below the muffler and carburetor. It is attached with two screws, and has a breather valve built into it. Do not touch the breather valve when you remove the valve cover: it is fairly delicate. Note the black gasket which keeps the cover from leaking oil: do not damage it - if it becomes damaged it will have to be replaced.

Look behind the valve cover: you will see two coil springs, and just below them, the junction between two metal parts: the tops of the two tappets, and the bottoms of the two valve stems where they emerge from the coil springs. To see how the valves operate, pull the starter very slowly with the spark plug removed: you will see each valve in turn rise and fall. Turn the engine to Top Dead Center at the end of the compression stroke - both valves will be closed. At TDC or very slightly past it, you need to measure the valve clearance, which is the very small gap between the top of the tappet and the bottom of the valve stem. To do this you use a set of "feeler gauges", which are very thin strips of hardened steel. Each gauge is marked with its thickness. The intake valve clearance should be 0.005-0.007". The exhaust valve clearance should be 0.007-0.009". If both clearances are about right, reinstall the valve cover, ensuring that the engine still turns smoothly and freely afterward.

If the valve clearances are correct and the camshaft timing gear mark aligns exactly with the crankshaft timing gear mark, you are ready to reinstall the crankcase cover with its gasket.

OK, Looks like I have to remove the Fuel tank first? to get to the valve cover. But to remove the fuel tank I need to remove the air filter. I am a bit wary of removing anything considering my last efforts. Are there any tricks here?

I think you can do this just by removing the carburetor, fuel tank and air filter all in one piece, Stuart, though I haven't done it. There are just three nuts/screws to remove: the two holding the carburetor to the cylinder's inlet port, and the one holding the bottom of the fuel tank. See the red circles on these two diagrams from the parts list:



The speed control cable from the handlebars will still be attached to the fuel tank, but I think there will be enough slack in the cable to allow you to put the whole assembly to one side while you access the valve cover.

Since I haven't actually done this, I hope Joe Carroll or someone else will chime in and confirm it can be done this way.

Thanks. Given that I have a 50% chance of having the tappets in the right position, what will happen if we work towards getting the engine started. Will it be obvious if they are the wrong way around and if so can I then take the gasket cover off and change swap the tappets over. It may cost me another gasket but is it better than taking the other things apart? One of the guys at the auto shop where I bought the feeler gauges also mentioned gasket paper. Is this an option?

If the tappets are the wrong way around, most likely one clearance will be more than it should be, and the other less than it should be or no clearance at all. The other possibility is that by luck, the two tappets are the same height and so the clearances are the same. If you had experience in this, I would suggest that you start the engine and listen to it, since a substantial difference between the two tappet sounds would be obvious. However since you are not accustomed to the sound, I do not think you would notice: you would just hear one tappet sound, and not be able to compare it with the usual two sounds.

Remember that to start the engine you must clamp the crankcase cover into position. After that if you have to remove the cover again because the tappets are the wrong way around, it is possible that your new gasket will be destroyed. This is additional to the possible replacement of the valve cover gasket.

If the tappets are the wrong way around, and as a result one of them has far too little clearance - or perhaps none - sustained running of the engine in that condition will cause one valve to burn, requiring another engine job to be done: lapping (if you are lucky) or replacing the burned valve. If you were unlucky, the valve seat would be damaged as well, requiring a somewhat more difficult replacement.

These risks are not unmanageable, and I think quite a few competent home repairers would "take the punt" and run the engine as it is - but those are people who would notice if it suddenly had uneven tappet sounds.

The decision is yours to make, Stuart. I am personally biased toward "doing the whole job" in cases like this because if you compromise the outcome to avoid removing those additional parts, you will end up being frightened of engine jobs in future. It is traditional to advise people who are thrown by a horse, to get back on it immediately and win the psychological battle with themselves.