Researching Engines 671TI in '79 37C

[Bob Bradley]

My daughter and son in law bought the subject boat last year. I've been doing some digging on it, as they don't have any specs on the engines. Turns out it was owned by one of our own here - Hcalmar, who unfortunately is no longer with us. I've been digging through his posts and see that early on he indicated that it had 671TI engines making 390 hp. Several years later he responds to another member who asked about performance in the same model, and he stated his performance but indicated that he had 310hp 671TI engines.

At this point, I'm trying to determine what the max load and no load rpm should be for these engines. I've heard anecdotally that the load max rpm should be either 2300 or 2500. We are fairly certain that they are the J&T version, but don't know the hp. We're also trying to determine what the original props would have been.

Presently, she's hitting 2106 port and 2256 stbd under load. I've set the rack, timing, and valves, and have canceled out each injector to check for cylinders not firing. Each injector did drop the rpm when interrupted, however one on the port side seemed to have slightly less effect than the others did, so I suspect it may not be performing properly. We're going to change that one, and it probably explains the 150rpm difference between the engines.

That all well and good presuming the engines should be making 2300 rpm. Clean bottom and minor prop tuneup should correct that. But, if the rpm should be 2500, then clearly the props need to be detuned. Marking on the props is pretty much impossible to read.

So, do any of you know what the max load and no load rpms should be, and what the likely hp actually is?

Here's a link to a pic of the boat from Hal's profile. http://www.samsmarine.com/gallery/showimage.php?i=425&catid=member&imageuser=32

 

[rsmith]

All 71 series and 92’s should be 2300 wot underl load and 2450 no load. The HP rating doesn’t effect governed RPM. 53 series where different I believe 2800 no load.

 

[rsmith]

37 is a really nice small big boat. Lots of interior room and a large FB for a 37’ boat. My neighbor has one repowered in the 90’s with 450hp yanmars boat is a 25kt cruise boat. Only downside I’ve found it bucks like a bronco in a head sea. I think it has to do with the length width ratio.

 

[Captain Ralph]

With the serial numbers, J&T will tell you what was delivered as far as the HP tune, injector size and if the cam was advanced.

Move that suspect injector to another hole and see if it is weak there.
You may be miss-leading your self on this is why the engine wont make RPM.
I ran a boat with 6-71Ns. One of the lungs had burnt exhaust valves. Lots of smoke mid range but still made loaded WOT. The governor just gave the other lungs more fuel.

IMO; WOT is against the governor, not the injectors.
If un-loaded RPM is close, I would look at fuel supply or turbo if not making that last RPMs.

BTW; is was common for techs to raise the governor to 2500+ RPM on busses. Gave them a bit more umpha on hill climbing.

 

[brettportzer]

I think our 671N's are rated by J&T to be 310hp.

 

[Semiahmoo]

I think our 671N's are rated by J&T to be 310hp.

Correct.

 

[Bob Bradley]

I'm still getting conflicting information on these engines. DD in Middletown CT tells me they should turn 2500 loaded and 2700 no load. J&T referred me to Egg Harbor who tells me they should turn 2300 loaded and 2500 no load. We're pretty sure they are 390hp. I called JT back and explained the contradiction and they told me to call back tomorrow when "their guy" is back in the shop. It's been pretty frustrating.

 

[cenger]

Bob,
My last boat had J&T671TIs rated at 410hp. Loaded max RPM was 2300, unloaded was 2450. A plate onthe engine hatches showed the RPM range and held true to actual performance.

 

[Lmcruiser]

I don’t know about in a 1979 boat but in Mid 1980’s J&T 6-71 TI engines were rated at 450hp and WOT loaded 2500 rpm. My 1988 Viking has J&T 6-71 TIB’s rated at 485 hp and loaded WOT at 2500. The WOT unloaded is 2600. I actually have J&T chart with power / fuel consumption curves that is on my boat in storage right now or otherwise I would post them. It covers both engine ratings TI and TIB from J&T.

 

[captcrunch]

Bob, when I had questions on mine I spoke to this guy. He’s one of their old school guys Jeff KnottJT Parts Dept.Mt.Laurel BranchParts Direct Line856-234-3570

 

[Bob Bradley]

Thanks guys. I suspect that it should be 2300 loaded. Especially since it's 390hp and your 410 is that. Seems to stand to reason that they might have run the higher rpm models faster. Stbd is turning 2256 and port, with a suspect injector is doing 2106. Port is likely holding stbd back a little.

 

[Bob Bradley]

Unfortunately one engine placard is missing and the other is mostly illegible.

 

[Captain Ralph]

Unfortunately one engine placard is missing and the other is mostly illegible.

Serial numbers are stamped on the blocks.
Call on your J&T or real DDC guy with them.

Probably not going to get new tags but DDC offers an illustrated part breakdown (IPB) manual with the original and current part numbers for your engines, per serial number.
Lots more than those lil tags offer.

 

[Bob Bradley]

Serial numbers are stamped on the blocks.
Call on your J&T or real DDC guy with them.

Probably not going to get new tags but DDC offers an illustrated part breakdown (IPB) manual with the original and current part numbers for your engines, per serial number.
Lots more than those lil tags offer.

Yea, Ralph, I've got the serial numbers, but I'm still back at square one until I can get the correct rpm specs. And the J&T resources are contradicting each other.

 

[Captain Ralph]

If you can, please post the model number, serial number and injector model (N90?).
I have some old DDC notes, Some make mention RPMs depended on the injector model.

Your 390 HP rating; I can't find that exact HP rating in my notes.
Is that flywheel (SAE) or prop shaft HP?

 

[Bob Bradley]

The 390hp number came from the survey and old For Sale ads. J&T tells me the 671TIs only came in 410 and 450hp. S/N is 6A0380585. Model is 10633303. Injectors are N90.

Props on this '79 37C are 23 x 22. Today we pulled out the spare props and found them to be freshly reconditioned. Note on prop says "-2" pitch and "23 x 19". I intend to put them on in the spring in hopes of getting the RPM up where it should be

 

[Captain Ralph]

The 390hp number came from the survey and old For Sale ads. J&T tells me the 671TIs only came in 410 and 450hp. S/N is 6A0380585. Model is 10633303. Injectors are N90.

Props on this '79 37C are 23 x 22. Today we pulled out the spare props and found them to be freshly reconditioned. Note on prop says "-2" pitch and "23 x 19". I intend to put them on in the spring in hopes of getting the RPM up where it should be

I'm SWAGin that the 390 is shaft HP, The larger 410 is SAE flywheel HP. Same engine. Larger numbers help the sales folk.

I'm assuming you use 1.460" for injector height.

I have the data on the 450. Let me look further for the 410.

Any documentation on what the original props were and size?

 

[Bob Bradley]

I believe the 23x22 were the original props. I checked the chart and believe that these engines use the same injector height as my old 6v92ta engines, so I'm using that gauge. It's been in my toolbox so long that I can't read the numbers on it any more

 

[Bob Bradley]

I measured my injector timing gauge and it's about 1-15/16", which is 1.468, so I'm guessing that it's the 1.460 gauge you noted.

 

[Bob Bradley]

Sorry. 1-15/32" or 1.468. Fir some reason I can't edit posts on my phone.