91 175 Intruder Cylinder Heads

[car1568]

Hi Folks

I am about to rebuild my 91 175 Intruder and after looking at the parts list I noticed that the part numbers for the block and heads lasted for 1 year only.
91 Heads - 0335196
91 block - 0434567
92 onwards heads - 0338311
92 - 93 block - 0435282

My questions are:
. Where there significant changes between the 91 and later model blocks?
. Same again for the cylinder heads?
. Can I put the later model heads on and is there much to be gained in doing so?
. with .030 oversized pistons would I need to go up a size in highspeed jet 72 - 73?

Thanks in advance for your help.
Cheers

 

[Faztbullet]

Re: 91 175 Intruder Cylinder Heads

Where there significant changes between the 91 and later model blocks?

Yes.. The 91 crank is different on the ends, The 91 uses a different lower seal housing which is NLA so dont break it, uses pressure back rings, lower drain nipple different, early style motor mounts and little more port timing...

Same again for the cylinder heads?

The later model has a tad bigger CC's in chamber and camfer....

Can I put the later model heads on and is there much to be gained in doing so?

Maybe a tad better idle due to little lower compression....

with .030 oversized pistons would I need to go up a size in highspeed jet 72 - 73?

Anything I build over .020 goes up 1 size....
The 91 150/175 was the hotter(hp) engines but most troublesome due to way casted/made. Make sure you have block pressure tested before any machine work and due the updates (intake gaskets/grey spark wires/sealing plugs on throttle body)

 

[SparkieBoat]

Re: 91 175 Intruder Cylinder Heads

how do you pressure test the block??

 

[Faztbullet]

Re: 91 175 Intruder Cylinder Heads

Bolt the heads on,bolt block off plate and gasket to block bottom,attach block off plate and gasket to rectifier opening, pressurize with air (50-60 psi and apply soap solution to casting lines externally and submerge block and look for bubble coming from cylinders...

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

Yes.. The 91 crank is different on the ends, The 91 uses a different lower seal housing which is NLA so dont break it, uses pressure back rings, lower drain nipple different, early style motor mounts and little more port timing...

The later model has a tad bigger CC's in chamber and camfer....

Maybe a tad better idle due to little lower compression....

Anything I build over .020 goes up 1 size....
The 91 150/175 was the hotter(hp) engines but most troublesome due to way casted/made. Make sure you have block pressure tested before any machine work and due the updates (intake gaskets/grey spark wires/sealing plugs on throttle body)

Thanks Faztbullet. Given the CC is small on these heads I will not be changing.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

Thanks Faztbullet. Given the CC is small on these heads I will not be changing.

Hi FaZtBullet, sorry but I just re-read your reply and I am confused by what you mean by throttle body plugs. everything else will be done or has already been done. Can you tell me which item number it is on the diagram below?

http://www.**********/images/diagrams/brp/IMAGES/434267/14.png

Thanks again

 

[Faztbullet]

Re: 91 175 Intruder Cylinder Heads

You just clean and seal the core plugs(round disks) on the aluminum throttle bodies....

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

I have another question regarding sealant.

What's best to use on the heads around the water passages? (Planning on permatex hi temp silicon)
I was planning on using Permatex Aviation #3 on the crank case.

Cheers

 

[SparkieBoat]

Re: 91 175 Intruder Cylinder Heads

I use the black gasket maker, it high oil resistance. but I would assume that what you planned to use would work fine.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

Here's some pics of the rough bore.

Cleaned up the tops of the pistons tonight while I'm waiting for the correct socket to undo the conrod bolts.
I had a sneaking suspicion that this motor had been stripped down before and it was confirmed when I discovered that one of these cylinders was already 030 oversize. Luckily it's not the one causing my concern atm.

Now I only need to get the other 5 cylinders bored and honed to match.

 

[SparkieBoat]

Re: 91 175 Intruder Cylinder Heads

it is best for all cylinders to match for sure.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

it is best for all cylinders to match for sure.

Exactly!!

I have built/rebuilt a number of car engines for road and race use and I would never think of only doing 1 bore and piston. Yet it seems to be common practise in the boat world, I just don't get it. Any engine builder knows that a balanced engine will perform better and last longer.

 

[SparkieBoat]

Re: 91 175 Intruder Cylinder Heads

too many shysters in the outboard world...I am currently rebuilding a motor that was supposed to be a fresh total rebuild, I got from a local crook.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

OK Status so far.

Block going in for machining today.
All parts ordered.

Only complication so far is the 1 oversized cylinder has signs of wear, looks like the ring has picked up on the port. Hopefully deburred and honed and it will be OK, fingers crossed. I gave it a quick hone and it's much better but lets see what the experts say.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

So after a long wait the block is back from machining.

It's been so long I have forgotten which direction the pistons should face.
I know the Oil hole in little end faces up.
Pictures of the port and startbord pistons in block, with markings visible (No Rods fitted).

The skirt cut outs seem to be identical.

Does the EXH stamp face into the centre of the V or out?

 

[boobie]

Re: 91 175 Intruder Cylinder Heads

Edit.

 

[car1568]

Re: 91 175 Intruder Cylinder Heads

OK Folks, I have got this thing back together and it fired up and run well on the ears in the drive way.
I am running a pre mix of 50:1 for break in, which turned out to be an engine saver.
I dropped it in the river and took it out and the thing coughed out the carbs and stalled. Put this down to not being run for a while, primed the line up again and hit the elec primer during start and away it went. Idle out through the 4 knott limit was about to open it up and the oil horn came on (Thank f#ck for premix). Hit the primer on the oil line and the horn went off. This happened a few times and I'm putting this down to the system needing to beprimed.

Now for the bigger issue, a number of times the motor would miss and cough through the carbs and stall. Each time I reprimed with the bulb and it would fire back up. Note the bulb had no pressure in it. I have deduced so far that it's a fuel issue (Call me a rocket scientist) but I'm not sure where to start on this, I have no visible leaks in any of the lines. I did notice after wards that I have a crack in the red lever for the fuel primer and when activated fuel came out. I am ordering a replacement for this but I'm not sure that this is the main issue.

I'm looking for a few items to investigate before splashing out on a new fuel pump.

Cheers