A-4 exhaust

[nicholasdeem]

proud owner of my loyal A-4,

few questions????

kinda stupid but oh well here i go..How hot should the exhaust discharge get ,I had a folding chair get near mine today in the back bin and melted and was ready to catch fire, made marks on the exhaust wrap and scorched the wood on my gaf it was warm.... well I know your going to ask ,,what is your engine temp ...I am running 130 degrees on the gage.

second question my boat is slow, sloth like...yes I have alot of weight on it it is my live aboard,, I can run about 1400 rpm's no more and bottom pretty clean about 3 weeks worth barnacles, scrape this week but I am thinking time for a new Carb, or fuel pump is to big drowning the jets....it runs clean on the plugs..

Thanks guy's

[smosher]

whats the size on the prop ?

What model boat do you have ?

I wouldn't change anything yet

[Kelly]

As for the temperature of the dry exhaust, if that is what we are talking about, the answer is "very hot"! In this part of the exhaust the pipe temperature is basically reflecting the temperature of the gases exiting the manifold following combustion so you can imagine the mercury rising.

If you are talking about the exhaust section farther down the line and downstream of the cooling water injection point, the answer is "not very hot at all". In my boat, I can hold my hand on this section indefinitely.

The dry/hot section should be wrapped with good quality exhaust heat insulation in order to avoid fire hazards...as you have nicely demonstrated with no serious harm done

[sastanley]

we probably have more questions than you!

The hot section exceeds 250F...The temperature of the water/exhaust mix in the exhaust line is closer to what your gauge is reading, but it is still hot. The water exiting my engine and into the exhaust is about 115F. I probably can't hang onto the hose like Kelly...

I agree with smosher..we need more info..a "bogged" motor is usually either a dirty/fouled prop, or sometimes an over propped condition. At any rate, 1,400 is pretty low.

A dirty bottom will make a little tiny bit of difference, but a dirty prop makes a huge difference in the engine's performance...several hundred RPM. Depending on your location, a few weeks is all it takes. I notice I lose about 250 RPM off cruising RPM and have a much harder working engine with only 3-4 weeks of barnacle growth on the prop. I am in the mid-Chesapeake Bay area.

[nicholasdeem]

30 foot Grampian

30 foot Grampian is the size you ask and the prop is a two blade, pretty sure it has been updated from the original, 6 0r 8 inch not totally sure.

more concerned that the fuel pump is maybe to large forget the acuall gpm..

Nick

[sastanley]

Nick, thanks..more questions!!

What type of fuel pump? electric? manual? If electric..Facet? Got a model number? The A4 when properly tuned burns something on the order of .75 to 1 gallon per hour..the fuel pumps I think are usually well over this reading...the real measurement is the PSI the pump is pushing to the carb..a fuel pressure gauge in line would help answer your question about too much fuel. A couple PSI is all the A4 needs.

The float valve in the carb is supposed to hold the fuel pressure back. If it is malfunctioning, you can end up with fuel puddling in the bottom of the carb/flooding, etc..

Most 2-blade props for the A4 are in the 12" diameter range. The pitch is usually more of a concern...too much pitch doesn't allow the A4 to spin fast enough. That being said, Indigo makes a 10" diameter x 7.4 pitch 3-blade for the A4.

The original two-blade 12" x 7" pitch prop on my C-30 (10,200 lbs., x 25' LWL) allowed about 2,050 RPM wide open with a clean bottom & clean prop @ 5.7 knots...cruise speed was about 5.1 at 1,700RPM. The three-blade Indigo has the same top speed, but at 2,250 RPM, & my cruise RPM is about 1,850-1,900 RPM at ~5.2 knots.

[nicholasdeem]

Prop

My fuel pump is Faucet number wish I was at the boat but I'm not I do know it is over 10 GPM, has been on for over a year, what would the ideal pump cost and what is it?

second what is the best prop out there, Idigo , seems some like and dislike, I think three is better, just seems like one extra blade would add more push maybe not....did see I think new blade at Moyer or somewhere for the a-4 was painted white 2 blade, like to know which to invest in..
Nick

[Mo]

Hi Nick,

For your G-30 you will find better overall performance with the 3 blade. They are a heavy boat (the glass in your hull is about an inch thick). The exhaust will get hot and cause melting on the chair...no doubt. Last Sept I put 2 packages of the wrap stuff on mine when I rebuilt the hot exhaust...it stunk for a couple of days and was fine after. Next time you have to rebuild the hot exhaust look for a more isolated area to run the pipe. On my C&C 30 the lazarettes were open and you could go down one and up the other...I put plywood bulkheads in so that anything I'd have in the lazarette would not go near the exhaust, shifter, and prop shaft. FWIW. It's been a few years since I've been around a Grampian 30 and forget your layout. It would be good if you could take a few pics with a digital camera, your exhaust layout and pump...worth 200 words these days due to economic situation. LOL

[sastanley]

Nick, Don't worry about props and stuff now..take some time to learn the boat & motor before throwing money at it.

[ILikeRust]

take some time to learn the boat & motor before throwing money at it.

Bah! I scoff! HAH! Why would you want to do that, when you can do like I did? Buy the boat in August, try to replace the head gasket in December, snap off a stud, have it towed to a boatyard in January and blocked on the hard, then pull the engine and tear out the cabin sole!

Then, while doing a complete tear-down and rebuild of the engine, buy a new propellor, replace the cutlass bearing, have a new shaft coupler fitted and faced, repack the stuffing box, replace the stuffing box hose, tear out the engine compartment forward bulkhead and make a new one, make new floor timbers, paint the bilge, re-bed cabin-top grab rails and other leaking deck hardware, replace and re-bed cabin port lights, tear out and replace the raw water intake through-hull, make a new battery box...

Have a brand-new main sail made!

And - to top it off - have a brand new bimini, dodger and sail cover made! (Them are EXPENSIVE ).

Yeah, I've done all that in the past 8 months. The boat is still on the hard in the boatyard. But at least the engine is back in the boat, and it now is bolted to the beds and the prop shaft is re-connected.

Next up: hook up all the new plumbing (including a brand new MMI FWC kit), wiring and re-connect the exhaust (assuming nothing in the exhaust needs replacing (fingers crossed).

[sastanley]

OK Bill, I had a new main and cover made before I ever sailed the boat, & skipped the other canvas for now, but except for yanking the motor, I've got most of those other items checked off too.

maybe you are a little more aggressive than the rest of us.

[nicholasdeem]

boat over haul???

Man and I thought I had it bad,,no it,s been a fantastic boat for the $700 I spent on her and always starts right up, no serious problems with the A4 either, just little slow , I am going to scrape it today, and I know I have lots of wieght inside, 3 batteries, fridge, every bin is packed.

I just started fresh water flushing the motor, yeah I know neglected but it has been so good to me I need to protect the internals.
may pull it out inthe next month due some upgrade sto the motor and paint it out and rebuild.

I can't complain, I have a car right now that has coste dme over $8,000 in transmission work and do not want the boat to start being an issue.

Nick, thanks for all your help, it is appreciated.

[nicholasdeem]

prop

the prop while scraping today is not that big at all, if I was too estimate the two blades are like 6 no more than eight inches long and about 2 1/4 wide/???

seems small for the size boat..

Nick

[biohead]

timing?

Hi Nick,
I have been "negotiating" with the 1980 vintage A-4 in Weebs for a few months. She recently came out of a three month refit in the yard during which we installed a new exhaust system, prop shaft drip less packing, tune up, water pump....

At some point I got the firing order wrong causing the timing to be off by 90 degrees. (all the wires shifted over one plug on the distributor) We discovered/fixed the problem by rotating the distributor until it fired. We were on the hard so I didn't want to run the engine too much and we left it in that position.
A month later in the water, the engine seemed to run fine and I forgot about getting the timing adjusted in. What I found was that the hot part of the exhaust was very hot, much hotter than before the replacement. I attributed the increased temperature to the new insulation and didn't think about it too much. She was starting and running well, maybe a little hot but not too bad.

As the weeks went by I noticed that she would not run well with the throttle in the idle position, it had to be set a little higher to idle well....and later still I noticed that in forward she wouldn't get up to speed (RPM) as before. Last week she wouldn't start at all.

What I discovered was that the timing I had ignored was retarded. Apparently in the yard I left the distributor just barely close enough to correct allow the engine to run but way retarded. As soon as I adjusted the distributor cap she fired right up and as I set the timing back to normal RPM came up, power went back to normal and the exhaust temperature dropped considerably. In hindsight this all makes sense: the engine couldn't make use of the energy in the fuel because the spark was too late in the power stroke of the piston (lower power), and the fuel was still burning on the way out of the cylinder (hotter exhaust).


So in a nutshell check the timing.