OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Crankcase Gasket on Mower Engines

Hi All,
I was wondering if anyone had experience of using a RTV silicon to replace the very thin paper gasket on the crankcase?
I have some thicker gasket paper to make a gasket but it may affect tolerances such as crankshaft to cylinder and also the valve lifters. Have any members tried the silicon with success or failure?

Hi rollo, can't remember trying it on mower motors but I can't see it being a problem, not like bits of the RTV can get caught in the oil pump or oil ways, the thickness of the gasket should make no difference to the pressure on the top and bottom bearings, not like they are a critical tolerance machine

Whoa it does make a difference. You be surprise how critical the clearances are. You maybe only running a few thousands of an inch clearance with the gasket and have zero to negative clearances without the gasket.

If the engine calls for a paper gasket it best to use it. Now with the gaskets are commonly .015" though thinner or thicker may for clearance to be right. There are engines the use RTV, Honda bond, Yama Bond for for the sealant but the clearances are spec'd for this use. I do know if you try to assemble an engine that uses .015 paper gasket it will lock up as you tighten the screws.

When using RTV you need to use the surface prep spray so the RTV adheres properly. Before I started using the surface prep spray the valve covers I installed would start leaking in a short time leading me to redo my work. Also on the engines that uses RTV or other sealer, the sealer basically just fills in the imperfections otherwise it is just squeezed out.

Everybody perception of what is paper thin varies too.

I agree AVB, but it is not like it is going to cost a lot of time and money to give it a try. I know when I was rebuilding lots of Enfield motors a few years ago, depending on the gasket set you got from India, you either got a thick or a thin timing cover gasket, I usually was able to use the thin gasket on the older motors because things were a bit worn but on the newer motors I had to use the thicker gaskets because the thinner ones would lock the motor up. Might have also had something to do with Indian machining tolerances as well

By way of explanation, I bought a Rover mower at the local tip shop, seemed ok and with a basic service chugged along quite well. However, it has now fallen victim to the dreaded "not cleaning under the base syndrome" and has rusted out where the handles attach. I have a Masport base which takes the Rover catcher and is solid aluminum so set about swapping over. All good until the last of the bolts holding the engine decided not to come out. Rattle gun, heat, all the usual no avail until finally the head snapped. Had numerous older BS motors so got a oil pan housing off one of them (seems the same ( I hope) except for the oil drain, so it will have two oil fill points). Cleaning the replacement housing I was taken by the amount of sediment in it and thought a good service/rebuild would need to clean it out as it would contaminate any new oil and increase wear. It is fairly easy to get the housing off but the cost of replacement seals could blow the budget if done regularly, hence the silicon alternative. I agree with both of you, if the mower is relatively new, yes paper seal, but if the engine is old then silicon, as with the amount of gunk in the oil grinding the valve cam and crank seal they would be fairly sloppy. I will give the silicon a go and let you know how it went.