View Full Version : Reverse Rotation Conversion PCM 351
04-26-2010, 03:01 PM
So I don't own a mastercraft :x but I figured I would try posting this here anyway. I currently have a 1985 Dixie Superskier 299 with a Ford 351 that I am working on restoring. It is a reverse rotation engine and I was wondering why this is (balance the driver weight?) and what could be bad side affects of using forward rotation engine instead. I know I will need a new prop, water pump, starter, distributor, and change the tranny pump direction. (most of these parts need to be replaced anyways and forward rotation is cheaper). One reason for wanting to do this is I am having trouble finding anyone who can grind a reverse rotation roller cam (any ideas on this?). Has anyone done anything similar or have any reason why one might want to leave it reverse rotation.
04-26-2010, 03:20 PM
We have had 2 DIXIE skiers at Bay Area WaterSports the last 2 years. One we SOLD. I thought it rather interesting when the boat backedup what MC Owners call the WRONG WAY. The same was a CC. All the parts you need are still available for the motor configuration. Getting the starter rebuilt will be about $80 more that regular rotation starter. Prop rebuild is the same. Trans parts parts are the same. I am not going to go into how to change the direction on the trans. I would suggest keeping it original. There was a reason to run reverse rotation on that hull. Don't know why but I sure there is. It is not that much more to keep it original
04-26-2010, 05:33 PM
Jim is correct- boats designed with RH props (driving the decision to go with reverse rotation engines) were done so for a reason. Nearly all older Correct Crafts (pre-1989) were designed this way- and all the CC direct drives still swing RH props. Counteracting the weight of the driver is one of the major considerations. Jim is also correct that it wouldnt cost that much more to keep it RH.
Switching to LH will make the boat ride and handle differently. If the Dixies are like the older CC's, the hulls werent built symmetrical- they were designed with a RH prop in mind.
If you want a RH roller cam, then the only place I know of to turn would be LSM Engineering (http://www.lsmeng.com/). They can build you a custom billet blank, but make sure youre sitting down when they tell you the price.
RH flat tappets are still available, and Cam Research (http://www.camresearchcorp.com/)can build you a custom cam for a ski boat better than anyone else I know of.
04-26-2010, 05:41 PM
Not sure how to break this new to so many great boat folks.... the motor is built the same for either RH or LH!! The firing order is the only difference I know about, having torn down and rebuilt a Holman Moody Motor for my old Mustang 16 by CC.... The trans is set up for the RH or LH. The rods and bearings are the same, as is the cam/roller having held all in my hands, once upon a time:)
04-27-2010, 08:24 AM
Thanks for the input
I will probably be keeping it reverse. I have spoken with cam research and comp cams who can both grind the flat tappets. I will probably go with cam research because I've heard good things about them and they have the cam break in (which is still cheaper than comp cams without). I haven't heard back from comp on whether they can do reverse rollers. I feel like I could get some more power out of a roller but I'm not exactly how the different profiles will affect the possibility of reversion so I will be doing some research there to stay safe before deciding.
04-27-2010, 09:15 AM
The opening and closing ramps on a roller cam are different, probably not enough to see, but different enough that you can't just run the engine the other way.
There is nothing at all wrong with switching to flat lifters. You may need to change pushrod lengths, but that is really easy. The flat follower cam profile will be a little less aggressive with opening and closing ramps, but I doubt it will make much difference in real world performance, especially in a boat where low end torque is far more important that top end horsepower.
On a side note, ALL the rollers in an engine (lifters, rockers, roller chain) are for friction reduction and give virtually zero performance increase.
04-27-2010, 10:13 AM
He wouldnt be changing to flat tappet- he would be keeping it. The roller conversion will cost about $1500 on a reverse rotation engine. The custom billet blank and grind will cost about $1k, then you need the tie bar roller lifters... not cheap. Rollers make more power and are more realiable, but you can buy a lot of flat tappets for the cost of one roller in this instance! You can still make big power with a flat tappet.
Definitely go with Cam Research- they dont leave power on the table with their grinds. They know Fords (thats all they do) and ski boats... Comp cant hold a candle to them for this application.
Boxman, thats a pretty misleading post. RH and LH engines vary a lot more than the indexing of the transmission... I think your memory is failing you! Besides all of the accessories that Jim mentioned (distributor, starter, etc), the cam is a totally different piece, and the rear main seal (or wick lines ground into the crank) are different as well. If the pistons have offset wrist pins, then they need to be installed backwards. The other internal parts are the same, but theyre not the same animal.
04-27-2010, 10:32 AM
Do you have the specs of your engine including cam grind?
Right now I have GT40 heads ported and with 1.94 intake valves, Edelbrock performer intake (already had this so no rpm), this bottom end is an open slate I have to get a new block since it was cracked. 408 sounds fun but isn't really in the budget. Any reason if I were to find a cheap roller core (the guy at cam research made it sound like they used to have them) I couldn't just go with a roller block out of say a 90's truck with a 351 (are the seals different)? Basically I'm trying to decide what engine I want to pull or I might have some other lead.
04-27-2010, 10:51 AM
I dont have the specs handy. Pick your bottom end first, then match the heads and intake, then pick a cam last. Cam Research will make a good recommendation based on your chosen components (including compression ratio) and how you plan to use the boat. I can tell you that the GT40 heads and Performer intake would choke a 408ci, so if youre set on using those, then stick with 351 cubes. If youre rebuilding from scratch, pick some pistons that will get you in the 9.0-10.0:1 compression ratio range- assuming youre ok with running 91+ octane. Follow the piston manufacturer's recommendation on piston to cylinder wall clearance for a marine application.
The 351w's did go roller from about '94 on, at least in the F-series trucks. I dont believe any marine engines were roller though. Dont bother with a roller block unless you plan to go LH or spend big bucks on a custom cam... but that money would be better spent on more cubes or better heads, IMHO. You can convert any block to roller (just drill and tap for the spider retainer), or just go with tie bar lifters. The latter is a better solution, though pricey.
You may have trouble finding a reverse rotation rear main seal- that will be the trickiest part. The one piece directional seal is getting difficult to find these days. If you can clear that hurdle, then I would build a 9.0-9.5:1 RH 351w with your GT40 heads and Performer intake, add a Cam Research Cam and call it a day. That should put you around 320hp, with a huge improvement in holeshot and midrange power. Top end will be a little better as well, and I would prop it to turn 5000-5200.
Almost forgot- dont forget about a modern CNC (Acme or OJ) prop. That is the single most important performance upgrade you can do.
04-27-2010, 02:02 PM
I probably will be doing exactly what you said. Any idea where to find a 1 piece rear main seal?
04-28-2010, 12:31 PM
Honestly, I dont know if anyone has them in stock. All of my RH Fords are pre-1980, which is about the time that the block/seal changed, so I havent had a need. I would check with SkiDIM or a few CC dealers. I know the guys at Race City Marine (http://www.racecitymarine.com/) were looking into having a new run made up due to availability issues... so that would be worth a call as well.
04-28-2010, 05:57 PM
Called race city still waiting to hear back from them there local actually. Also found out I can get on from PCM for $96. At this point I have to get a new block though can you see any reason to not just go with an older 2 piece block? I won't base my decision on the seal but it could make me lean this way.
Thanks for all the feedback
04-29-2010, 11:59 AM
The older blocks that used the 2-piece seals used non-directional seals. They relied on the wick lines in the crank to pull oil away from the seal. Your crank wont have the wick lines, so it will leak. I am not certain if the cranks themselves are different between the block styles, or if its a seal difference only. I would say your choices are:
a) have some wick lines machined into a smooth crank and use the older block
b) use the RH specific rear main seal
If you found one in stock for $96, BUY IT! That will by far be the easiest route.
04-29-2010, 12:11 PM
Those old two piece seals always eventually leaked anyway.