mac 21 ob

[Mike Larson]

Gunna jump..... Bob..... the score in the piston was possibly a slipped piston clip?........ check yours.... it may have bounced around on the top end, and done what it done.......

J Dub- what can be done FIRST to remedy the finite needle deal, for basically I have that same search ongoing..... ie: whupped timing and work = picky and fickle..... basically searching for the ease of pain on the engine for reliability..... volume, clearance, or what?.... being you cant normally change timings once theyre done, I've seen quite a few ballistic Mac's that have to have the planets aligned to run........ granted each situation/motor/pipe is it's own, knowing the basic factors to have the engine at least comfortable to needle, and run, would be great, and still gain the potential horsepower the motor has to give....... Not to raid bob's post, by far, but the constant/control, of, setting a .21 anywhere from .006 to 8, or 10, and throwing high nitro to it, still gains most guys the plug issues they ask about....... too many variables with nitro, pipe, and timing out there, but, if a simple lower/bigger volume button or something else combined eases issues, lets know..... thanks mike

 

[LarryConrad]

I run all my .21 engines at .006-.007 head clearance I have never had an issue with eating plugs, I run K&B 1L or McCoy MC 9's depending on air and water temps....In Minnesota that can vary from sub zero to sub tropical, for the air temps,and several feet of ice to high 80's F for the water temps.The Mac on my Nemesis has a Silver Bullet HP pipe measured from the center of the cylinder to the first crease on the pipe is 8 3/4". I run 60-70% fuel with 14% Klotz synthetic oil. X437/3, 40X53,M440,1440 b/c, X442 for props depending on water and weather conditions. I have never had problems getting my Mac outboards to scream...Just problems finding a hull that would stay on the water when they are screaming.

Larry

 

[bob miller]

Gunna jump..... Bob..... the score in the piston was possibly a slipped piston clip?........ check yours.... it may have bounced around on the top end, and done what it done.......

J Dub- what can be done FIRST to remedy the finite needle deal, for basically I have that same search ongoing..... ie: whupped timing and work = picky and fickle..... basically searching for the ease of pain on the engine for reliability..... volume, clearance, or what?.... being you cant normally change timings once theyre done, I've seen quite a few ballistic Mac's that have to have the planets aligned to run........ granted each situation/motor/pipe is it's own, knowing the basic factors to have the engine at least comfortable to needle, and run, would be great, and still gain the potential horsepower the motor has to give....... Not to raid bob's post, by far, but the constant/control, of, setting a .21 anywhere from .006 to 8, or 10, and throwing high nitro to it, still gains most guys the plug issues they ask about....... too many variables with nitro, pipe, and timing out there, but, if a simple lower/bigger volume button or something else combined eases issues, lets know..... thanks mike

thanks for the tip...i will check mine...bob

 

[Jerry Wyss]

J Dub- what can be done FIRST to remedy the finite needle deal, for basically I have that same search ongoing..... ie: whupped timing and work = picky and fickle..... basically searching for the ease of pain on the engine for reliability..... volume, clearance, or what?.... being you cant normally change timings once theyre done, I've seen quite a few ballistic Mac's that have to have the planets aligned to run........ granted each situation/motor/pipe is it's own, knowing the basic factors to have the engine at least comfortable to needle, and run, would be great, and still gain the potential horsepower the motor has to give....... Not to raid bob's post, by far, but the constant/control, of, setting a .21 anywhere from .006 to 8, or 10, and throwing high nitro to it, still gains most guys the plug issues they ask about....... too many variables with nitro, pipe, and timing out there, but, if a simple lower/bigger volume button or something else combined eases issues, lets know..... thanks mike

I duh'no Mike, maybe move to Minnesota :lol: ,, 3rd channel needle would be a better fix I 'spose,, course thats once you get the

button volume and headspace right. The latter I believe is the core issue for getting any engine on the right path. Alot of very expensive 21 o/b powerheads come with a bunch of volume in the button and the same with headshims. I think all it really is from the manufactures perspective is "anti-Ka-boom insurance"

I have a Mac buggy engine I was thinking of putting on the thunder tiger lower unit. Just for you information, the Mac "Buggy" is the same exact engine as the o/b,,, with an inboard type crank,,tic,tic,tic (finger nail tapping)

The idea was to give the Mac "a leg up" so to speak with a little more leverage with the geared lower. I have the pin installed in

the crankpin that drives the TT pto ("lights" did it, Mark Leyde),, but I keep setting it aside for engines I know that aren't going to be that temper-mental,, Big on the mental

 

[LarryConrad]

J Dub- what can be done FIRST to remedy the finite needle deal, for basically I have that same search ongoing..... ie: whupped timing and work = picky and fickle..... basically searching for the ease of pain on the engine for reliability..... volume, clearance, or what?.... being you cant normally change timings once theyre done, I've seen quite a few ballistic Mac's that have to have the planets aligned to run........ granted each situation/motor/pipe is it's own, knowing the basic factors to have the engine at least comfortable to needle, and run, would be great, and still gain the potential horsepower the motor has to give....... Not to raid bob's post, by far, but the constant/control, of, setting a .21 anywhere from .006 to 8, or 10, and throwing high nitro to it, still gains most guys the plug issues they ask about....... too many variables with nitro, pipe, and timing out there, but, if a simple lower/bigger volume button or something else combined eases issues, lets know..... thanks mike

I duh'no Mike, maybe move to Minnesota

Jerry, It's hard enough to talk him into making the 4 hour drive up here to race!

 

[julianconde]

i have had not issues with my engines maybe we should trade boats lol i use a bob violet needle valve i have to if not it will be madness lol

 

[Mike Larson]

Both feet now..... Jerry..... gonna wear that fingernail out....... I'm interpreting from the info provided, that buggy timing is what youre instilling....... and, granted, on a few radically timed engines I have, ballistic sure..... launch... maybe....

Basically and to test clearance and volume theory on a nova proving a dud in weeks previous..... the thing had a funky black button in it with finger ports ala a kb, maybe a keely, but I've never seen that animal. Motor spun up well, takin plugs religiously, hot. Volume on the button was monstrous, IMO, and the clearance was @ 10, so, it ran, but not to potential, and way hot, with the consequent plugs crying in pain.....

Stock crank timing, no piston work, it's just... there. A consequent install of a standard OEM button and clearance, (I'm still at 10), will seek me testing it further....... Investing in Mccoy, and not liking it........

Got my D wheel back....... syringe for volume..... until the button lathe materializes, I have to work with what I have, I guess........ ( shims, and clearance)........ sucking elements, and overheated plugs surely warrant concern, at least for me....

Larry..... we're working on boats to come up there....... we'll see..... employment is goal, for me, at least....... The tunnel crew is coming around nicely........

Thanks for sharing, Dub, and MD, curing the sickly engine world..... ...... mike

 

[LarryConrad]

Both feet now..... Jerry..... gonna wear that fingernail out....... I'm interpreting from the info provided, that buggy timing is what youre instilling....... and, granted, on a few radically timed engines I have, ballistic sure..... launch... maybe....

Basically and to test clearance and volume theory on a nova proving a dud in weeks previous..... the thing had a funky black button in it with finger ports ala a kb, maybe a keely, but I've never seen that animal. Motor spun up well, takin plugs religiously, hot. Volume on the button was monstrous, IMO, and the clearance was @ 10, so, it ran, but not to potential, and way hot, with the consequent plugs crying in pain.....

Stock crank timing, no piston work, it's just... there. A consequent install of a standard OEM button and clearance, (I'm still at 10), will seek me testing it further....... Investing in Mccoy, and not liking it........

Got my D wheel back....... syringe for volume..... until the button lathe materializes, I have to work with what I have, I guess........ ( shims, and clearance)........ sucking elements, and overheated plugs surely warrant concern, at least for me....

Larry..... we're working on boats to come up there....... we'll see..... employment is goal, for me, at least....... The tunnel crew is coming around nicely........

Thanks for sharing, Dub, and MD, curing the sickly engine world..... ...... mike

Mike,

Change your .21's head clearance from .010 to.006 and you'll be amazed at the difference...even with that 45% fuel you like so well.

 

[Jerry Wyss]

Both feet now..... Jerry..... gonna wear that fingernail out....... I'm interpreting from the info provided, that buggy timing is what youre instilling....... and, granted, on a few radically timed engines I have, ballistic sure..... launch... maybe....

Basically and to test clearance and volume theory on a nova proving a dud in weeks previous..... the thing had a funky black button in it with finger ports ala a kb, maybe a keely, but I've never seen that animal. Motor spun up well, takin plugs religiously, hot. Volume on the button was monstrous, IMO, and the clearance was @ 10, so, it ran, but not to potential, and way hot, with the consequent plugs crying in pain.....

Stock crank timing, no piston work, it's just... there. A consequent install of a standard OEM button and clearance, (I'm still at 10), will seek me testing it further....... Investing in Mccoy, and not liking it........

Got my D wheel back....... syringe for volume..... until the button lathe materializes, I have to work with what I have, I guess........ ( shims, and clearance)........ sucking elements, and overheated plugs surely warrant concern, at least for me....

Larry..... we're working on boats to come up there....... we'll see..... employment is goal, for me, at least....... The tunnel crew is coming around nicely........

Thanks for sharing, Dub, and MD, curing the sickly engine world..... ...... mike

Hey Mike, go over to General Boating Forum and look at "Decreasing Compression", There's some good input there,,Mike Huges perdy much sum's it up along with stuff from Steve Wood.

I see some Nova 21's with a "flat piston" and a angled squish .18cc in the bubble or .23cc with the angled squish included. That scenario ain't ever gunna work right,, but I have a Top 7port that has the same button but a "domed" piston w/ a dish and that can work,, or work better. I have that Top engine starting with .007" H/S and I'm going to squeeze that space until the plug & needle tells me its too much volume. Then I'll get on the lathe and turn that angle squish down a few thousandths,, actually I have another done and ready.

My OS 21 VZ-M on a TT lower has a "flat piston" with an angled squish and .16cc in the bubble alone, and I don't care what it is with the angled squish measured in too cause its hauls donkey! Thats the kinda stuff you should look for,, the headspace is something I actually screw with when I think I'm on the higher button volume side.

dub

 

[Mike Larson]

Jerry..... Mike's post was spot on, and very good. The dished/domed piston thing throws me for a loop on the novas, as I'm almost going to go back to the 'ole solder squish concept........ easy enough to clearance a flat top, but they are the exception to the rule anymore......

Most of my novas have the 3 degree .17cc button..... I have a couple .19's in there somewhere...... they are all around 10 thousandths, which, have them running well....... this may be disguised, as with the domed piston it may be less/better, and dished more.... Are there variances in the heights/depths of the piston tops you have found?... Basically I dont work on them enough to have searched this out....... a way to measure it would be nice, as, the micrometer method is almost a guess.......

Discarding the black finger ported nova button, per almost 0 volume, angle idk, and replacing it with a standard oem one, may help this thing. Mike's post described actually the symptoms, it had exactly...... I dont just wonder if it were a european, low to no nitro thing......... i'm not real fond of a sickly engine.......

Could it be assumed, also, then that less angle would keep the charge spread to the sides,or on the center of the piston?.....

Apparantly, the aftermarket lathe turners around arrived around 3 degrees somehow, like by examining the piston top for burn, and burning up sleeve sides?

For the most part, the 45/16, i run, with the 3/17 button, has exactly 0 ill effects on the button, or piston top, and very very clean...... a stars aligned thing, maybe...... I've relied on Arch to build my stuff, and he does very well..... it's the other parts junkers and experiments that have found to be challenging........ thanks mike

 

[Jerry Wyss]

Jerry..... Mike's post was spot on, and very good. The dished/domed piston thing throws me for a loop on the novas, as I'm almost going to go back to the 'ole solder squish concept........ easy enough to clearance a flat top, but they are the exception to the rule anymore......

Solder!! jezz man, get outa the dinosaur brush and get some Plastigage,, if ya need some I'll send it to ya. One problem to over come using plastigage is some Nova, RB,Top, Mac engines are very tight in the pinch when new.

I oil the piston/ sleeve thru the plug hole , heat gun the engine and see if I can get the piston over the top. It may take several attempts with the plastigage but is gotta be better than solder. The plastigage wrapper has a scale printed right on it for measuring the smashed width of the plastigage.

Some piston/sleeve are so tight that you have to use other measuring methods,, none of them fun. But, I figure that piston is going over the top at some point and I'd rather have it done when its well oiled and hot than out by the pond, cold and about to suffer several impact's of a starter!

The headspace is ,at the very least, the one thing you have to know before starting,, I don't think we'll hear any arguement over that.

 

[Mike Larson]

Jerry.... I've used plastiguage..... it always seems to chop off and let the piece fall into the motor........ finding solder with small enough OD around here proves a chore too...... Had a suggestion on a micrometer tweak i'm on to next........

Heating the thing for initial measurement sure is a good idea... Using washer/spacers to hold the sleeve down too.

I had, McGraws clearance guage, but the dial indicator didnt make it, and still have the glow plug part of it........ is there a source to obtain the replacement indicator ( without being dumb, as, in layman's terms it's like a 0 to 1 inch or something).... while subsequent machine shop searches 'round here had a few they wanted an arm, and the tip I needed wasnt right......... and inaccurate readings can be made with the dish/domed nova apps....... I get EnCo flyers, but lack for getting the wrong tool.....

Super trick deal would be for a cone lock initial piece made, too..... maybe an adapter?........

Auto store has plastiguage.... here we go..... thanks mike