OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines blowing clouds of smoke

My Cox lawnboss is playing up (its almost new, 20hours) yesterday on a job it lost revs then stopped; it would fire but not run - pushed it onto the trailer. Got home checked the oil, it was low so topped it up (I was assuming it was the Low Oil Cut-out in play)today after 5-10 minutes it started billowing huge clouds of white smoke,LOTS of smoke, any ideas what the problem might be - the local dealer went bankrupt several weeks ago so warranty is a drama & I need it for daily work
edit: its a Briggs 16.5hp Intek

I am not too familiar of the new briggs motors but I am fairly certain that the engine breather could have something to do with it, I have seen youtube videos where near new ride ons have the crankcase breather get blocked or jammed and they smoke like crazy.

I think you are right Joe, just have to figure out where it is/what it looks like and see what I can see, any further advice still appreciated!

I think it would be a bad idea to take the machine apart since it is presumably under warranty, and you may cause problems with that by getting on the spanners. However the first guess I would be making is that you ran it out of oil, it seized up, came free when it cooled down, but by then it had broken the rings and/or scored the bore fairly badly, and it now has very severe blow-by. The first thing to check is whether it has compression, because that is a non-dismantling test for what I have suggested.

Remember, the Inteks/Vanguards have an automatic decompressor, so compression should not be exceptionally high anyway at cranking speed. However normally an Intek can't even turn over on the electric starter if the decompressor is not working, and doesn't spin all that fast when the decompressor is working. Does it spin faster now on the electric starter than it did?

Grumpy, it wasn't that low on oil, there was still oil on the dipstick...I finished the job with no smoke....I just took it for a run up / down the street and no smoke, could I have overfilled it a bit causing burn-off?
Will check back later, have to do a quote

It sounds as if it may have just gulped some oil into its breather for some reason (such as the engine being tilted at some point, and/or the sump was over-filled with oil) and has cleared itself. That does not explain the original shut-down though, unless it was due to low oil as you thought. So, perhaps the oil got low, the engine shut down, something happened during the service that got oil into the breather hose, it's now gone, and all is well. It would be good to know how the oil got into the wrong place, though, so we could be sure that's all it was.

I have seen reports that Intek engines are prone to producing heavy white smoke if they are run on a cross-slope, left side down-hill. However one of the accompanying explanations of why this allegedly happens (blown head gasket) is not sufficiently detailed to convince me. A blown head gasket could certainly cause the problem, if it was blown between the combustion chamber and the pushrod compartment running into the crankcase. However this would only happen on a new engine like yours if the engine design was poor (as claimed in the report) or the cylinder head was badly installed. Here is that report:
http://www.fixya.com/support/t1910391-14_5hp_b_s_ohv_looses_powes_blows

Here is a miscellaneous set of reports, some of which make sense to me and may be relevant:
http://www.fixya.com/support/t2674300-see_lot_white_smoke_out_outlet

The number of reports of this problem with Intek engines is a bit of a worry - it may be something the engine is prone to. There are three themes in the explanations:
1. Mower was running on a cross-slope when the smoke happened. In this case you just have to watch and learn what your mower is capable of. Remember, Briggs and Stratton specify that you do not run the engine on any more than a 15 degree slope.

2. Mower was over-filled with oil when it happened. Note this could be due either to putting too much oil in the sump, or the carburetor flooding and petrol passing through the main jet into the intake port, past the valve, past the piston rings, and into the sump, so there is petrol in the oil, and the oil level has a tendency to rise, not fall, with time. If this happens you need to fix the flooding carburetor, and probably also make a habit of turning off the fuel when you park the mower. Rising oil level with an air-cooled engine that has gravity fuel feed, always means fuel or water is getting into the sump. It needs to be fixed immediately, and the oil changed.

3. Mower had a mechanical malfunction causing high crankcase pressure when the smoking happened. In this case, the problem will be recurrent. The breather tube will contain oil if you stop it while it is still smoking - in fact in a severe case the tube may blow off due to the internal pressure. Case three is the one I posted about earlier in this thread; if the rings are broken or worn out, or the head gasket is blown into the push rod space, blow-by will cause high crankcase pressure, and high crankcase pressure will blow oil into the breather system.

quick update, local mechanic reports a blown head gasket - badly blown apparently

I was going to suggest a gead gasket but it shouldnt have happened on such a new engine, wither the head/block was never machined perfectly or somehow the head wasnt torqued down properly a gasket failing on its own for no reason is pretty rare in my books.

Joe, I've seen a report that the Intek/Vanguard (i.e. large OHV) Briggs engines have a design fault: the bore is too close to the pushrod space, and the gasket is prone to blowing in between the two. This would happen more easily than you may expect, since the OHV engines are high compression (8:1, where the side valve engines were 6:1). See here:

http://www.fixya.com/support/t1910391-14_5hp_b_s_ohv_looses_powes_blows

I hadn't regarded it as a credible report, but it is starting to look plausible now. Redeye, thanks for giving us that outcome, it makes this thread a more useful one in the archive. We'll see if more people report blown head gaskets with Intek/Vanguard engines, over time. Most of the reports we see here are on older, side valve engines - we haven't had many cases yet with the OHV engines. Head gasket problems do occur with the side valve engines, but nearly always due to assembly errors.

I'll close this thread.