cold start bore wear

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Apr 19, 2006
Albuquerque NM
I'm new to this list so bear with me if I'm beating a dead horse.
I'm in the midst of a "debate" with another shop owner. Our discussion involves cylinder dilution and bore wear at cold start especially with older carburated vehicles.
I've suggested adding a small amount of 2 cylce oil to the fuel tank (or Rislone, which he said was viciously picked apart by this list) to mitigate some of the enevitable wear.
What say you?
Twenty five years ago I worked for a small engine manufacturer. We had one single model that suffered wear on the face of the intake valves due to the valves actually spinning from the twist of the springs at certain rpm's (Actual valve rotators spin the valves only when they are off the seat.)

To determine whether the wear was from friction or impact from poor cam geometry, I tried running the model on a test dyno using 50:1 two stroke mix and the intake valves looked great. So, yes I think that running two stroke mix might help a little with bore wear. Some RX-7 enthusiasts use it or Marvel Mystery Oil to supposedly help with rotor seal wear.

However, On the test engine, the exhaust valves were extremely carboned up from the added oil, so there may be unwanted side effects from adding it. We switched the engine to more expensive stellite hard-faced valves and the problem was solved. Cars would already have hard-faced valves and seats.

I wouldn't add any oil to my cars' fuel. The one exception that I have personal experience with this is to use up what's left in my outboard's tank at the end of the season . . . and then I put it in my winter beater and dilute it as much as possible.
Most of your cylinder wear is unavoidable. It's not due to any lack of lubrication. It's due to the piston not being fully expanded upon startup (and for a good time afterwards). There's also the inherant nature of the piston exhibiting its thrust on the wrist pin, making all of your cylinders oval eventually.

Plenty of carb engines can make it for the long haul if the carb is kept leak free and the service duty isn't of a perpetual short trip nature.
While I understand that wear is unavoidable over the course of the engine's usable lifespan, our discussion is specific to oil film dilution due to cold start and the use of chokes or cold start injectors.
What I'm trying to hear on this forum is opinions as to whether adding small amounts of 2 cycle oil or similar products (Rislone, Marvel Mystery Oil, etc.)directly to the fuel could have any long term detriments.
This discussion was instigated by owners who wanted 50 year old engines run beyond the typical
rebuild mileages they were accustomed too. Like 200,000 miles instead of 100,000.
A solution would be to add oil injectors such as used on many modern power plants..
Run an inverse oiler on the engines. Filled with Marvel Mystery Oil, they will provide plenty of lube to the cylinders.
An aggressive choke can certinly wash oil from the cyls.
Marvel Mystery oil in the fuel, or maybe some 2 stroke oil will help, some.
The cyls. are one area that gets lubed almost instantly, from splash and piston movement.
My thinking is to ensure proper choke operation.
Cyl. wear just isn't that big of a deal. I've seen too many abused engines with over 100,000 miles on them, and there is still a lot of cross hatch left.
Modern engines have lower tension rings, and tighter tolerances, and are even better.
That device certainly might work to fill the void.
I might point out that valve jobs used to be the bread and butter job of most shops but since the introduction of unleaded fuels I haven't seen a dozen valve jobs for all the old reason in years. Oh, and valve seat recession, nope didn't/hasn't happened. In fact my customers who continue to use lead additives are the ones still experiencing problems with carbon build up and sticking valves.
Gary Allen,
What is MMO?
I've been reading some of the other posts on this thread and it is full of acronyms that I have no notion as to what they stand for. Is there a glossary for these terms some where in this site?
Thanks. I certainly wouldn't recommend 50:1 or even 20:1. perhaps just enough to help coat the bore walls. I can't see where it could hurt. Probaly would help with sticking valve issues too.
I would use Lucas UCL fuel additive. Can get it for around 25 bucks (gallon jug) at the truckstops. Mix 3oz per 10 gal fuel. FWIW the problems I have seen with fuel wash are wear in the upper cylinder, but the carb has to be in pretty bad shape. I would use 15W-40 truck oil in my older carburetor cars.
Oops, I guess this device (Accusump)really wouldn't work for top end cold starts. Ideally suited for racing where oil scavenging occurs.Looks like Mr.Rigby's suggestion is the way to go.
Independent studies have indicated that up to 50% of wear on engine components occurs during the engine start-up, before oil pressure can be established by the oil pump.
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