Mercury XR4 rebuild break in question

[Heliguy78]

Good afternoon! I have a 1988 Mercury XR4 that I just finished a complete rebuild (pistons, rings, cylinder work, bearings, ect.), and am wondering about oil mix during the first 10 hour break in period. The service manual is confusing in that in one section it talks about tank mixing the oil with the fuel at 25:1 during this period, however it says nothing about premixing in the section specifically about oil injection pump equipped engines (which mine is). I really don't want to wear this engine out before it's properly broken in, and I don't want to tune my engine with a bad fuel/oil mixture. What is the happy medium with this?

 

[racerone]

Is the oil injection in service ?----Did you replace the plastic drive gear on the crankshaft when motor was apart ?--------Myself I would run the motor at fast idle with 25:1 mix and do a test on the oil injection pump output before trusting it.

 

[Heliguy78]

Yes I put a new bushing and gear in it during the build. The pump seemed to be working when I had it all apart (oil in all lines). But your right, I'll give it a good test to ensure operation.

 

[Texasmark]

Yes I put a new bushing and gear in it during the build. The pump seemed to be working when I had it all apart (oil in all lines). But your right, I'll give it a good test to ensure operation.

Butting in, the 25:1 Racerone mentioned is 50:1 mix in the tank in addition to the normal oil pump addition to the fuel....if working properly.....safety net incase it has a bubble or doesn't work.

Mark your oil tank level and run that tank of premix out and measure your oil consumption (if any) from the tank. Say your fuel tank pre-mix was 6 gallons. 50:1 would be a pint of oil consumed per 6 gallons of gas. Get a quart of TC-W3 and fill the oil tank back to the original level. If most of your consumption was at WOT, then it should take one pint of that refill quart to get you back to the mark you made on the oil tank. If you did a lot of low speed running to burn that 6 gallon you will not have used a full pint as the ratio as I recall is 80:1 at idle and varies to 50:1 at WOT so your test wouldn't be all that accurate and since it is on the "using less oil" side of the pendulum, it's not a valid test that your pump is working properly.

That's the way I see it.

 

[Dukedog]

what kinda piston did ya use?.. standard, oversize?

 

[Coxwain]

Does the oil tank needs to have tight caps on it or can they be loose for air ?

IS there any other way to test an oil pump while it is installed?

 

[Faztbullet]

what kinda piston did ya use?.. standard, oversize?

Best question asked so far.....