Prop shaft question

conchy joe · Post by **conchy joe** » Mar 21st, '12, 11:32

I just got one motor back from the machine shop and I am waiting on a parts shipment to start the assembly process in my 28 Bertram gas to diesel conversion.

Anyhow, I am building 155HP cummins 4bt's with IRM220A 1.53 trannies.

I stopped by Bobby Soles Propeller and wanted to talk shafts and new struts. He listened to what I was doing and plugged some info into his computer and said that I could keep my 1 1/8" inch shafts going with 17X20 props still have a safety ratio on the shafts of "3".

I want to spend my money smartly and if its reasonably safe to not spend the money and time on larger shafts/installation I do it.

What do you guys think?

CaptPatrick · Post by **CaptPatrick** » Mar 21st, '12, 12:15

Joe,

Did you talk to Robert or Jim at the WPB location or someone up in Stuart?

In Memory Walter K · Post by **In Memory Walter K** » Mar 21st, '12, 13:33

I don't know if this helps or bears any relevance but when I converted to 210 Cummins 6bt's with 1.52 trannys from Chryslers, we kept my 1 3/8" shafts. I turn 20 x 20 cupped props and have been doing so since 1990.

Charlie J · Post by **Charlie J** » Mar 21st, '12, 15:23

walter
iam running 1 3/8 on my yanmars 230s no problem
1 1/8 seems to be on the lite side joe, just my 2 cents

In Memory of Vicroy · Post by **In Memory of Vicroy** » Mar 21st, '12, 15:46

I think you should be fine with the 155 hp and the small-ish diameter props, assuming your shafts are in good shape, no cracks, etc. - spend a few bucks having them magna-fluxed and checked for straightness. I had an inch & a half AQ22 shalft snap off behind the strut on my B31 with the 250 6BTAs & the 1.53s. I try to rotate the shafts weekly if I can - the props are heavy and when left in one position for a long time will cause stress cracks....I think that's what happened to mine, but who knows - shapped off clean as a whistle and never recovered the porp and stub shaft even tho it happened in my slip. Mud eats loose props in a nono second.

UV

Bruce · Post by **Bruce** » Mar 21st, '12, 16:09

Don't, I repeat don't use the existing shaft length to set your engines. Your not gonna have much of any leeway fore and aft to play with current shaft length.

If your shafts are in top shape and Robert did the calculations then you have a good chance of them working out fine.

Good chance the length won't work out so you'll need new shafts. At that point consider going to 1 1/4.

conchy joe · Post by **conchy joe** » Mar 21st, '12, 17:15

Capt Pat: I spoke with Jim. I know he's the new owner. I said I was still good even if the shafts were the lowest PSI material.

Bruce: Can you explain the length issue, I'm not catching your drift.

Thanks.

PS Just found out the second engine has a cracked head. The kicker is that the first motor has 9mm injectors and the head was good and I could find an injector shop to rebuild them. The second motor had a newer head, 7mm injectors, and that was cracked. Also the injector shop it at a loss to find parts to rebuild the newer injectors.

Go figure.

In Memory Walter K · Post by **In Memory Walter K** » Mar 21st, '12, 18:14

If I remember correctly, the older injectors were the problematic ones whose tips dropped into cylinders and the newer ones were the correction to cure that problem. Hope I'm wrong for your sake.

Bob H. · Post by **Bob H.** » Mar 21st, '12, 18:28

Joe, Bruce is saying that the length of the shaft may be different than your current setup, IE..longer or shorter engine and transmission length. you can go up in shaft size (diameter) and use existing strut just use undersized cutlass bearings, which you should check anyhow after going this far...take a few extra steps...my ride is 6bta M3 370 hp 1 3/4 shaft..no doubt..BH

In Memory of Vicroy · Post by **In Memory of Vicroy** » Mar 21st, '12, 19:53

Look in Boats & Harbors - there are a number of places that sell new, complete heads for 4Bs as well as rebuilt ones. Not very expensive at all from the aftermarket guys vs. Cummins. The 7 mm injectors are the ones you want. Walter, the Bosch injectors that dropped tips were only used on the hopped-up 4BTA 250s - like Doc had, and Cummins came back and replaced and warranted all of them, including damage that was out of warranty.

UV

conchy joe · Post by **conchy joe** » Mar 22nd, '12, 07:05

I understand the length issue now.

I have one set off 7mm injectors and one set of 9mm injectors. The 9mm injectors were able to be rebuilt and 9mm head was good. My injector shop said he can't find parts for the 7mm injectors, but are available from cummins.

It's just ironic that the newer 7mm head to address the cracking issues is the one that is cracked.

Pete Fallon · Post by **Pete Fallon** » Mar 22nd, '12, 07:26

Conchy Joe,
If your going to repower why not go with new at least 1-1/4" shafts. Due to the age of the boat, the condition of shafts(around shaft log tightening nuts, {major wear area } cutless bearing tubes both ends and thread and key way conditions).
If it was my boat I would go with newer larger shafts just because of age and fatigue factor, if your going to keep the same shafts at least have them maga-fluxed and inspected by the prop shop, just to be an the safe side.

Bruce · Post by **Bruce** » Mar 22nd, '12, 08:04

Just a more detailed explanation on engine placement in the 28.

Engine height is critical if you want to close the hatches without major modification.

If your keeping the factory shaft angle, there is only one position fore/aft to line up the engine.

If your building new stringers, they along with the mount heights are determined by the shaft angle and where the shaft lines up with the output flange on the gear box.

Other considerations are exhaust placement for the cross over engine vs aft bulkhead clearance vs tranny cable movement vs clearance just to get down there and bolt and align the couplings together.

If your going from gassers with the velvet drive reduction gear, the shafts will be too short.
The output shaft of that 220 gear box tucks up underneath of the offset gear box vs the velvet drive which was an inline gear and stuck straight out the back.

What injector shop are you using?

Diesel injection in Riviera Beach, ask for Jack. Best around.

Bob,
Good choice on those 1 3/4 shaft diameters. I saw a bunch of those 370's with 1 1/2 shaft setups. Of course a good many were coupled to under rated gear boxes and before the shafts would break, the gear boxes blew.

conchy joe · Post by **conchy joe** » Mar 22nd, '12, 10:57

Bruce: Thanks for your explanation. I think I will go with 1 3/8" shafts, put new logs in and do new custom struts. That way I get the hatches to close and it will be less frustrating in the long run.

Also, yes I was dealing with Jack. Any suggestions on dynamic balancing the motors. I just static weighted the rods, piston, pins, etc, they is a range of 60+ gram difference between the four, or am I just being too anal?

Know of any shops in the area you would recommend?

TailhookTom · Post by **TailhookTom** » Mar 22nd, '12, 13:38

If you are going with new shaft logs -- why not try what Capt. Patrick was kind enough to layout on this site.

http://bertram31.com/proj/tips/shaft_logs.htm

conchy joe · Post by **conchy joe** » Mar 22nd, '12, 14:18

Oh, trusty me I've looked over all of his building tips and will be using his expertise!!!!!

I don't claim to know much, but I am smart enough to follow the advise/teachings of a master like Capt Pat.

Bruce · Post by **Bruce** » Mar 22nd, '12, 16:14

Since 4 banger diesels are rougher than a cobs ass anyways, I wouldn't waste the time or expense of trying to balance those engines out.

As you may already know, watch lowering the engine height to where either the oil pan hits the hull (ask me if I've seen hull domes where someone didn't pay attention to this)

Or the shaft angle decreases too much to fit the proper diameter props and have the proper clearance (seen this one too) after the engines were in, shafts and struts were set and the last item before sea trial was installing the props.

Got called into two instances where other dealers screwed up royally.

A well laid out agenda, block diagram, engineering list or what ever you want to call it from start to finish before the first grinder is taken to the job is essential to a well thought out repower vs a fly by the pants cost twice as much and looks like a Joan Rivers face lift.

Sorry if I state anything you may have already done or know.

luis · Post by **luis** » Mar 22nd, '12, 16:15

If you use Aquamet 22 , you can keep the 35mm cause they say that its the equivalent to the normal 316 at 50mm.
I'm gonna keep the old entrance with 35mm but this time with Aquamet 22 to run on Cummins 220 , mainly... because... I'm a bit afraid of doing the new ways like Capt Pat says, and also because the old ones are still in good shape... ( when I have to deal on the bottom part I become a litle chicken...)

All the best

Marlin · Post by **Marlin** » Mar 22nd, '12, 22:07

Shaft/strut replacement needs lots of prep work, when I did it I first supported the shafts with a wooden vee block fixture hot glued to the hull near the trannies,this gave me the proper orientation,side to side up and down, I measured the clearance on the cutlass bearing top an bottom, fore and, the goal would eventually be to be within .005 , carp pat used wedges, I had delrin collars turned that fit inside the new shaft logs and over the new shafts, should spin freely, take the struts to a shop, they will bolt them Down to a fixturing table, repeat the same process I just mentioned and weld the new struts to match the old orientation, Stuart prop has done over 40 of the b31', don't know about the 28' He does all the custom boats in the south Florida area, struts and rudder design ain't the same as straightening a prop

bob lico · Post by **bob lico** » Mar 22nd, '12, 22:14

tom did you do the capt. patrick f/g struct routine? i modified it and went out 4' ,worth at least a quarter of a knot at cruise and one half knot tab wot.

bob lico · Post by **bob lico** » Mar 22nd, '12, 22:26

joe you might want to consider a wooden engine jig .this with save you a lot of headaches . with the use of a cheap lazer flashlight like the one a teacher uses as a pointer mounted on the rudder you use a cheap engine freeze out plug with a 1/16 hole drilled in center then push into struct ,next white poster paper on area of output flange on gears BINGO there is a red dot exactly where the centerline of shaft will go on the gears ,if you go with captain patrick`s shaft log you can do all sorts of tricks to reduce shaft angle but that a long story.

conchy joe · Post by **conchy joe** » Mar 24th, '12, 09:40

Bob the wooden engine jig is a great idea. I was thinking about the laser pointer idea and decide that getting a laser bore sight for a rifle, then boring a hole into a wood dowel the same size as my existing shaft that would accept the bore sight would be a cheap and effective tool. Will keep everyone posted.

Bill Fuller · Post by **Bill Fuller** » Mar 24th, '12, 11:13

Joe,
You might find it usefull to go to www.sbmar.com and look at the two B28 repowers that Tony has provided articles for. Tony provides a very nice write-up for the repower of Noelle Mae and a good explanation of engine setup and alignment. These are Yanmar repowers but the problems and solutions are directly relatable to your 4BTs. My boat is Audax which was repowered in 2000, and the writeup is not nearly as informative, although some of the pictures may give some insite.
Good luck with your project.
Bill

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