GT 21 with 7.4 & Bravo One

[wighthorsepower]

Hello from over the pond in :england: I would greatly appreciate some advice on what to look out for. I am in final negotiations over a GT 21 in the UK. I believe the current Mercruiser 7.4 with a Bravo One outdrive has been put in during the last 10 years (? - I havn't managed to crack the year from the serial number yet) However it has been stored dry and everything about the engine looks unworn and unused. I am not sure what horsepower the engine is or what she is likely to get up to with a tail wind. Being a complete novice and new to Donzi's has anyone got any pointers? I havn't managed to find the serial number of the hull yet but I know her year of manufacture was 1975. Any help would be great. Cheers - Wighthorsepower

[Digger]

welcome to the board! And welcome to the Donzi addiction...

There are plenty of motorheads here more experienced than I to give you pointers, but I would suggest

-pull manifolds to look for extent of corrosion, particularly if there is any rust evident anywhere at the base of the manifolds
-pull the oil filler cap off and look in the underside of the cap. Condensation? milky residue? may have been sitting a long time/possible corrosion concerns
-how does the engine oil look? clean? milky?
-compression check of motor
-how does the drive lube look? clean? or not?
-pressure check on drive
-sea trial it and take it through the ringer

good luck and enjoy!

[wighthorsepower]

Thank you very much Digger. Sounds like very good advice and also for the welcome. I first made an offer 14 months ago. Its been a long road and I only was able to twig that she was a Donzi 2 months ago. Luckily Classic Donzi's are not that common here or I may have had some competition.

I have got to get some time with the engine but I did pull the dipstick and it was clean and pure. It hasn't turned in perhaps 4 or 5 years. Basically ignored and forgotten.

Thanks again - Wighthorsepower

[Morgan's Cloud]

WH
At the time that GT21's were being made , I believe ... stand to be corrected ... that they had HIN's on the transom. You say that you know it is a -75 .... Where do you get that info from ? It ought to be on the transom , unless the boat has been refinished and the number was obliterated.
The engine is probably around 300 hp at the prop... do you have any additional info on the model ? (7.4L/454 Mag etc)
The GT 21 is even a bit rare around here (even on this board) so I don't think you're going to bump into another one over there. What condition is yours in ?
Has it been re-done ?
I know what you guys call 'nice boating days' are small craft warnings to us :tongue: so enjoy it whenever you can.
Steve

[Ted Guldemond]

For what it's worth I have a GT-21, 1970 serial number 21-21. The manufactures plate is located on the right side of the central instrument cluster (the one that keeps you from easily getting your feet in front of you when you sit in the front seats). I've heard in later years the plate was placed on the left side. The main things I would look for is water in the transom core, look at the drain plug, usually a brass sleeve that corrodes and allows water into the plywood. Also look down the deck for any waviness or uneveness, this usually means the outer fiberglass skin is delaminating from the balsa core. In 1970 they used a galvanized steel gas tank, I don't know what they used in 1975. Any tank that old is suspect. Do not attempt to start the engine with 5 yr/old gas. Either purge the tank or use a temporary auxilliary tank with fresh gas. Good luck.

[wighthorsepower]

Steve

I shall look for a HIN and see what I can find. I have documents telling me who for and when the boat was commissioned but with the delivery and export over here it may mean that the actual manufacture could slip back into the last half of 1974. I am not sure what sort of production time was required between order and delivery back then, plus shipping time.

There is some untidy glassing (small areas) in the engine bay that probably happened at the time the later engine was put in. I hope it did not obliterate the HIN.

The only information I gleaned from the engine:

Mercury Marine Mercruiser
7.4 V8
Bravo
Thunderbolt Ignition
Power steering

Engine Serial Number: 00516958
Outdrive: 00550923

I havn’t gleaned the engine year from the number yet.

I knew there was something special about her and watched her a year before I cottoned on to the documentation that opened up the magical world of Donzi and identified her as a GT21.

With regards to be being re-done. She has certainly been repainted a few times, re-upholstered and re-engined. No Donzi badges obviously remain. I know she has been stored dry for her whole life and used intermittently. I will have access soon to original photographs taken at the time she was new.

Greatly appreciate your time. Thank you - Wighthorsepower

[wighthorsepower]

Ted

Really good to hear your experience and good advice. I shall look for the plate in the next few days. I shall also check the transom core and the deck. I will see how old the tank is and if it was replaced when she was re-engined. Thank you for the sage advice on the gas/petrol. Are you running the original engine or has it changed?

Another question if I may. Is there a register for GT 21’s and are there any estimates for survival against the numbers produced?

Thanks again - Wighthorsepower

[Ted Guldemond]

If you go to the home page and click on to Boat Registry, then sort by boat size, you will find if memory serves, about a dozen GT-21's. My boat has a 351 ford on a 250 volvo I/O. It runs 53mph by gps on an average summer day. My guess is that with a 454/Bravo you should run low 60's??? There are many 22 classics with big blocks on this site that can give you more accurate guesses as to performance characteristics.

[Rootsy]

Engine Serial Number: 00516958
Outdrive: 00550923


are you sure that the engine serial number is OO and not OD?

http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=7%2E4L+BRAVO++++GM+4 54+V%2D8+1988%2D1991

[BERTRAM BOY]

Do you know what the original color was?

[wighthorsepower]

Ted

Thanks for the tips. I am still finding my way around the registry. I will be coastal and offshore so conditions will be rare for for really opening up.

Thanks - WH

[Donziweasel]

7.4 litre stock was 310 hp at the prop, and weighs a bunch.

[wighthorsepower]

Rootsy

Yes I did mean D! Do appreciate your link. Thanks. I guess that makes the engine around 1990. The replacement with this engine probably happened in the Mediteranean. Are there likely to be any export records anywhere do you think?

Engine: OD 516958
Transom OD 491530
Drive OD 550923

Displacement 454
Ignition 8 degrees
Firing 18436572
RV8C
Rotation left
Max rpm 4200-4600
Idle rpm 650 to 700
plug gap .035

Prop - Mirage Quicksilver

Cheers - WH

[wighthorsepower]

Bertram Boy

The original colour was white with a blue stripe.

Cheers - WH

[wighthorsepower]

Donziweasel

We just moved the 21 and she was certainly a weight! Your 16 must shift though with that engine though!

WH

[Donziweasel]

Wighthorsepower-\

Had the 7.4 in another boat and did some work on it. 16 has a 5.7 that I am currently working over. The 7.4L was reliable, but weighed alot for only 310 hp. and most people I believe consider the 6.0 383 a better engine, especially with 330 hp and fuel injection. If you ever wanted to re-power, this would be a nice way to go. Love the GT's by the way. Good luck on the boat.

[wighthorsepower]

Ted

Looked for the number and there is no sign on the instrument cluster either side. I tried to look under the driver's seat but the screw thread was siezed. I believe that may be another hiding place.

No evidence of a HIN on the transom but it has been painted.

Cheers - WH