max rpms on muffs for a rebuilt motor

watermellonI

Petty Officer 1st Class
Joined
Jun 23, 2007
Messages
224
finally finished with a 1990 3.L rebuild can anyone tell me the max rpms i should run it on muffs? (if there is one) machine shop said to run the motor at about 2000 rpms for while, and stay away from idle once timing is set, but that seems a little high to me
thanks guys
 

Mkos1980

Chief Petty Officer
Joined
Oct 25, 2007
Messages
640
Re: max rpms on muffs for a rebuilt motor

finally finished with a 1990 3.L rebuild can anyone tell me the max rpms i should run it on muffs? (if there is one) machine shop said to run the motor at about 2000 rpms for while, and stay away from idle once timing is set, but that seems a little high to me
thanks guys


Sounds normal for breaking in the cam.
 

95yj

Petty Officer 1st Class
Joined
Feb 21, 2007
Messages
279
Re: max rpms on muffs for a rebuilt motor

You really want to keep a new motor away from idling as much as possible except for getting it running, timed, carb set, etc. The normal quote for breaking in a new cam and lifters is around 2000 RPM like your mechanic told you. The other problem is in seating the rings to the cylinders. You want to be running at different RPMs and different amounts of load on the engine without running too fast or pulling too hard. This will help break in your motor most efficiently.

To answer your question, there's not really a tried and true answer for running on muffs. You need to be able to supply enough water to cool everything along with the obvious issue of not free revving an engine, especially a new one, too high. Running between 1500 and 2000 to get the motor warmed up before you can fine tune it is not out of the question at all.
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,321
Re: max rpms on muffs for a rebuilt motor

personally.... on muffs i wouldn't run it higher than idle speed to maybe 12-1300rpms. The only exception is that if i'm checking timing i would blip the throttle to a couple thou for a milisecond to make sure the timing advances... i would never hold the throttle like that. 2K is to high.... 1500 is on the high side...
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,079
Re: max rpms on muffs for a rebuilt motor

The normal quote for breaking in a new cam and lifters is around 2000 RPM like your mechanic told you.

Ayuh,......

I Agree.........

After the Cam is broken in,..... Then go for a Boat Ride,+ finish breaking in the Rings,+ Bearings.......
 

watermellonI

Petty Officer 1st Class
Joined
Jun 23, 2007
Messages
224
Re: max rpms on muffs for a rebuilt motor

ok thanks a ton yall, now I just gotta wait for help to get it in the boat, could ya tell me a little more about "the boat ride to break in the rings"?
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: max rpms on muffs for a rebuilt motor

You need to load up the rings to properly seat them. The best way to do that is when you take it out on the water, after the engine warms up, go ahead and hit the throttle pretty hard for a few seconds, then let it come back down. Do this several times. This should help load, and thus seat the rings.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,079
Re: max rpms on muffs for a rebuilt motor

Ayuh,.......

Lots of throttle variations for the 1st 20hrs.........
 

a70eliminator

Captain
Joined
Sep 9, 2007
Messages
3,762
Re: max rpms on muffs for a rebuilt motor

The cam lobes rely totally on oil splash from the spinning crank to lubricate, hence the 2000 RPM. this 20min break in is the most critical once your by that it's all good. Just monitor the engine temp and shut down if temp gets much above 180 or so, a newly rebuilt engine will usually generate more heat than usual. On the lake vary the throttle like everyone says, power the engine up then back off, run at all different RPM's stay away from anything steady until after the first couple runs, by then the rings should be pretty well seated.
And as far as the muffs go, as long as your temp stays in range dont worry about it, just make sure your water supply doesn't get cut off like a kink in the hose or someone stepping on it, I think the main problem with muffs is if you have too much pressure the water will aereate and be full of air bubbles, you want to adjust the pressure just so your feeding ample supply to the waterpump and not causing aereation or for a better word cavitation. Good luck.
 

watermellonI

Petty Officer 1st Class
Joined
Jun 23, 2007
Messages
224
Re: max rpms on muffs for a rebuilt motor

ok, thanks again, had help today to get it in, but weather did nt co operate.
Lake is probly to low anyway, but Ill keep yall posted
 
Top