Mac 45 New Idea

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charles siler

Well-Known Member
Joined
Oct 29, 2011
Messages
2,004
Hi guys just bought a MAC 45 that had been equipped with a AA piston and liner it ran pretty good. I Not good with pretty good has anyone fitted a VAC 45 or a 46DD to the MAC45.The liners all fit with some work any favorites. The VAC looks most promising. Looks like clearance the rod match port and raise the liner 1.4mm and shave the button down to the plug and it looks pretty good. The Nova rossi looks like mabe a AA crank and cut the head down to the plug match port and it looks good to. Just seeing if you guy's have done any one of these procedures I'm looking forward to waking up these motors. Thanks pass ya later Charlie
 
I have a MAC that I puthink an A A p/like in and have not run it yet. Has the case been opened up on the exhaust port? I machined mine all out to accommodate the larger exhaust port. Our weather has been terrible so I am yet to try it.
 
I've been running mine for 6 months now without any case mods and it's a real screamer, i did use the AA button head as well with head clearance set at 12thou.
 
Okay truth be told this is the 2nd piston failure using AA pistons and I'm looking for and alternative or different perspective if you will its just a change. My CMB VAC45 is extremely hardy and I run most of my motor hard. The Nova rossi 46DD is super fast modded but I have broken two cranks I have some alternate parts and I see some other possibilities the other macs that I have are faster and are wearing out and I'm on the hunt for a better idea. Here's a pic of AA piston from last weekend.
 
Charles if i was you i would contact Scott Bouchie and get billet pistons done for your engines. as long as the sleeves are good he can make pistons for you all day.
 
1st one was a 45 JAE

2nd one on a twin 45 eagle outside motor

I would consider having Scott do some up but I would like a more cheaper approach to solve the problem.
 
I've also wondered if the VAC 45 Piston and sleeve would fit the Mac. I thought I read somewhere that they have the same bore and stroke but not 100% sure. I know the vac 45 rod is a drop in replacement. Considering you have these parts, measure them up and let us know how they compare.

As for the NR piston and sleeve, I believe the bore on that motor is smaller than the Mac due to its longer stroke which would lower the displacement of the engine. Theres a thread somewhere where David Wilfong was planning to give it a shot in another CMB case but Im not sure if he actually did it or not...

Out of curiousity, how tight were the AA pistons when you were running them? The only time I've seen that type of failure ( wrist pin pulling out through the bottom) was from running an engine too hard when its still tight.

Brian
 
I've also wondered if the VAC 45 Piston and sleeve would fit the Mac. I thought I read somewhere that they have the same bore and stroke but not 100% sure. I know the vac 45 rod is a drop in replacement. Considering you have these parts, measure them up and let us know how they compare.

As for the NR piston and sleeve, I believe the bore on that motor is smaller than the Mac due to its longer stroke which would lower the displacement of the engine. Theres a thread somewhere where David Wilfong was planning to give it a shot in another CMB case but Im not sure if he actually did it or not...

Out of curiousity, how tight were the AA pistons when you were running them? The only time I've seen that type of failure ( wrist pin pulling out through the bottom) was from running an engine too hard when its still tight.

Brian
both liners fit right in and are have a good fit .As fare as stroke the liner need to be raised about 1.4mm roughly to get the tdc clearance right . But I'm not spot on yet I'm doing this thread to get some help with it . The intake runner's are close and the exhaust needs some opening at the bottom of the case to breath right.

Both motors turned over pretty good with a light stick at tdc and we ran 1.5 to 2.5 gallons through both motors @55% nitro and 18% oil I have 13 other boats and I don't have this problem . My VAC has been super the NR super fast but I've had 2 crank failures and both are modded next crank will stay stock and modded lasted longer and was running mid 80s to low 90s.
 
I wonder that did you install new A/A 45 P/S into the MAC45 ? I can see damaged wrist pin " tight" and burn black and Piston was high friction ( holes wrist)
 
Charles spent lots of time pondering and measuring this scenario. the VAC 45 crank is a drop in the MAC case. the 46nova liner will fit but the rod pin is the gigaboo. It will work with a VAC rod and a custom piston. Get in touch with Scott Bouchie and talk with him. this was going to be my next move on this build.

I will work and bet it will be a rock solid eng that will scream.

Good luck hope you pick this up and run with it.

Have a new MAC45 case and crank on the for sale section that was planed on this build. The 46 P/L is already sold.

Also the VAC 45 back housing will not fit in the MAC 45 case. Maybe the AA drum will work? Never got that far.

David
 
Charles spent lots of time pondering and measuring this scenario. the VAC 45 crank is a drop in the MAC case. the 46nova liner will fit but the rod pin is the gigaboo. It will work with a VAC rod and a custom piston. Get in touch with Scott Bouchie and talk with him. this was going to be my next move on this build.

I will work and bet it will be a rock solid eng that will scream.

Good luck hope you pick this up and run with it.

Have a new MAC45 case and crank on the for sale section that was planed on this build. The 46 P/L is already sold.

Also the VAC 45 back housing will not fit in the MAC 45 case. Maybe the AA drum will work? Never got that far.

David
Hi David I would be interested in the rest of the mac 45 pm me some pics .I have already started on a version of both I'm just getting some basic information before someone says don't go that way for nothing. I'm thinking the AA crank for the bushing rod may be good for the NR 46DD but I need to measure it or that and a rod and not use the NR rod.
 
Charles spent lots of time pondering and measuring this scenario. the VAC 45 crank is a drop in the MAC case. the 46nova liner will fit but the rod pin is the gigaboo. It will work with a VAC rod and a custom piston. Get in touch with Scott Bouchie and talk with him. this was going to be my next move on this build.

I will work and bet it will be a rock solid eng that will scream.

Good luck hope you pick this up and run with it.

Have a new MAC45 case and crank on the for sale section that was planed on this build. The 46 P/L is already sold.

Also the VAC 45 back housing will not fit in the MAC 45 case. Maybe the AA drum will work? Never got that far.

David
Hi David I would be interested in the rest of the mac 45 pm me some pics .I have already started on a version of both I'm just getting some basic information before someone says don't go that way for nothing. I'm thinking the AA crank for the bushing rod may be good for the NR 46DD but I need to measure it or that and a rod and not use the NR rod.
 
I was thinking of cutting the VAC rod pin to fit the NR rod but then you have a weak point. I cut a old 45CMB crank pin down to fit the NR rod as a test cut.

The VAC crank and rod are pretty much bullet proof. Just need to balance the assy after the piston is made. Schott can do this also.

Just makes good senses to use the needle bearing steel rod.

with a custom piston you can also set the timings. If not the NR liner will subport the piston after you jack it around.

the trans ex timing's are to close with the NR liner and the VAC crank. the rod is also shorter on the VAC. this all adds up to a custom piston.

It is the best way with less work. just need to spend the cash on a run of pistons. then you will be set for a long time as thy will come a little large and you will lap them in. as the fit wears you can fit more pistons.

Get 5 piston made and it will hold you for a few years of running.

have a new old stock MAC 45 case never bin assy. also a new VAC .45 crank. look in the for sale section for it. If you want it let me know we can work a deal.
 
Thanks Dave but I'm lookin for plug and play disposal part idea . The main thing that I found is

1 you need a piston and liner and a head button.

2 approx. .050 brass plate

3 tools electronic digital caliper, coping saw drill and a dremel or fordem scratch all file and sand block divider.

Step 1 cut the .050 brass plate to shim the liner up.

Step 2 scribe the ports and grind the ports to match and really opening the exhaust port.

step 3 file the top of the head button down flat (there's a small raised area around the plug)

(Note) cmb and mac rods and cranks vary slightly they fit but you need to space the cmb crank about .030 thou.

Here are some progress pics.

I ran this motor last weekend and started and Idled really well. The motor work really well even though the installed deck height is about .002 to high witch should let it rpm a little more and a button shims at .008 thou .

I'm going to do more testing this weekend pass ya later Charles
 
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