Naive Donzi Question

[kincaidterrace]

I have a '87 Donzi 25 which was repowered with an Old School 7.4/454 GM long block roller engine. The boat has a high volume 80 p.s.i. oil pump, and a new steel crank, hasting rings, and com cam. I have owned it for two years and it runs and looks great inside and out. I have no issues with the boat and love it, but not too sound totally hopeless when I talk to my fine mechanic, I would be grateful if someone could answer a few very naive questions. So, please indulge me without laughing too hard.

1. What is an Old school motor, and why is it better for repowering old boats, or is it? My mechanic says that it has less fancy things that can break down.

2. What is a roller engine. Are these more efficient than other engines, or just different.

3. Does Com Cam stand for compression chamber, and if so I gather that comes with the new motor, since it is a "chamber", right?

4. When I was told that the boat had a new steel crank, hasting rings, and bearings and the surveyour agreed, I neglected to ask if these parts are integral parts of the engine, or whether they had to be purchased and installed separately. In other words when you buy a new engine, do you need to these parts separately?

Thanks.

[gcarter]

It might be a good idea to Google "Four stroke gasoline engine" and read a little about how such engines operate.
A good basic understanding is useful when a person wants to make heads or tails of some of the finer points....

[Planetwarmer]

I'm gonna let some of the very experienced motor builders answer all of the questions. However, I will say that if you have a 5.7 liter, you have a 350. If you have a 454, you have a 7.4 liter.

A "roller motor" has to do with performance modifications to the part of the engine that houses the cam all the way to the valves. The "roller parts" are components in between the cam and the valves. They are installed on the engine to reduce friction by using ball bearings where a stock motor will not have any. They replace the stock components and are a nice upgrade for a few extra horsepower.

Look up some of the parts on Jeggs.com that you have questions about. That will give you an idea as to what you are asking about, what they look like, and how much they cost.

[mrfixxall]

I have a '87 Donzi 25 which was repowered with an Old School 5.7/454 GM long block roller engine. The boat has a high volume 80 p.s.i. oil pump, and a new steel crank, hasting rings, and com cam. I have owned it for two years and it runs and looks great inside and out. I have no issues with the boat and love it, but not too sound totally hopeless when I talk to my fine mechanic, I would be grateful if someone could answer a few very naive questions. So, please indulge me without laughing too hard.

1. What is an Old school motor, and why is it better to repower for repowering old boats, or is it? My mechanic says that it has less fancy things that can break down.

2. What is a roller engine. Are these more efficient than other engines, or just different.

3. Does Com Cam stand for compression chamber, and if so I gather that comes with the new motor, since it is a "chamber", right?

4. When I was told that the boat had a new steel crank, hasting rings, and bearings and the surveyour agreed, I neglected to ask if these parts are integral parts of the engine, or whether they had to be purchased and installed separately. In other words when you buy a new engine, do you need to these parts separately?

Thanks.


i have annswers to all your questions but i wont answer because i will confuse the hell out of you...Com cam is Comp Cam's which who makes the camshaft in your engine..as for your surveyour he is full of chit ,you have to take the engine apart to figure that one out..he is probably going by the paper work..

[LKSD]

i have annswers to all your questions but i wont answer because i will confuse the hell out of you...Com cam is Comp Cam's which who makes the camshaft in your engine..as for your surveyour he is full of chit ,you have to take the engine apart to figure that one out..he is probably going by the paper work..

I agree & thought the same things.. :) Jamie

[MOP]

A simple question that will give us an idea of what you have is what is the top speed on GPS, we pretty much know what various versions of 454's will do. If it is worked over it will exceed the norms!

[joseph m. hahnl]

I have a '87 Donzi 25 which was repowered with an Old School 7.4/454 GM long block roller engine. The boat has a high volume 80 p.s.i. oil pump, and a new steel crank, hasting rings, and com cam. I have owned it for two years and it runs and looks great inside and out. I have no issues with the boat and love it, but not too sound totally hopeless when I talk to my fine mechanic, I would be grateful if someone could answer a few very naive questions. So, please indulge me without laughing too hard.

1. What is an Old school motor, and why is it better for repowering old boats, or is it? My mechanic .says that it has less fancy things that can break down.

2. What is a roller engine. Are these more efficient than other engines, or just different.

3. Does Com Cam stand for compression chamber, and if so I gather that comes with the new motor, since it is a "chamber", right?

4. When I was told that the boat had a new steel crank, hasting rings, and bearings and the surveyour agreed, I neglected to ask if these parts are integral parts of the engine, or whether they had to be purchased and installed separately. In other words when you buy a new engine, do you need to these parts separately?

Thanks.

question 1> old school motor uses a carburetor not fuel injection.

question 2> A roller engine means it use a roller bearing on the lifter"tappets" instead of a flat .
Generally they are referred to as lifters in a push rod engine and tappets in an overhead cam engine. The lifter rides on top the camshaft. The roller lifter "tappet", creates less friction so the engine is able to reach higher trouble free RPM


Question 3> what Fixall said "Com cam is Comp Cam's which who makes the camshaft in your engine"

question 4> a steel crank is referring to the crankshaft material.steel as apposed to cast iron. a steel crank is superior to a cast iron crank, it would have been purchased separately as it is not stock. Hasting is a brand name . the rings are short for piston rings. The bearings are for the crankshaft main , the connecting rods, and the camshaft.They are technically bearing surfaces and they do not have balls or needles that a bearing you might see on, say a bicycle . The bearings are designed to be the ware out part. as you would replace the bearing with out the need to replace the crankshaft or connecting rods.

Now again what fixall said, there is actually no way to tell what material the crank is made out of with out physically taking the motor apart.

This is a breakdown of the parts in question #4

#2 piston rings
#3 main bearings
#4 main thrust bearing
#16 connecting rod bearing
#17 crankshaft



https://www.mercruiserparts.com/images/CRUISER/97671/39.png

#7 camshaft bearings
#8 is the lifter
Note* The lifter in this view is not a roller lifter it is a flat tappet
#9 is the cam shaft


https://www.mercruiserparts.com/images/CRUISER/97671/37.png

[glashole]

and to clarify a little more

Old School is not a manufcturer of motors but rather a term used to describe the motor

this would mean that it would be using older style parts rather than newer technologies (like EFI) :wink:

[kincaidterrace]

Many thanks to all.
kincaidterrace