Rod slots???

[gselite2000]

I read about "Rod Slots" being cut when having Ruck work a block. What do these rod slots accomplish?

I have a block with him now, and if there is a lot of worth to it, I can have him do it before he sends it back to me.

Scott

[us1]

If its not an HP block there are huge gains. The gains are less with an HP block because the slots are already somewhat cut.

[gselite2000]

it is a 260 block. I run the crap out of my engines, so I was curious if it will at anything, or help it last longer.

Scott

[us1]

It will run better all around if material is only removed to enhance flow up the boost ports. Removing too much material only reduces the crankcase compression. This gives you a reduction in low-end and acceleration for more top end power.

[Prof. O/B]

It will run better all around if material is only removed to enhance flow up the boost ports. Removing too much material only reduces the crankcase compression. This gives you a reduction in low-end and acceleration for more top end power.

I think John hit it pretty well on. When he says "boost port", he is talking about cutting one (1) slot into the behind-the-liner ports (B.T.L.) only. This would be proper, as they are the "velocty ports" of the engine. While not limited to, they are the most important ports in controlling low-end power. The Charge moves very easily out of the crankcase into this port area because it is a direct feed. It is not governed by "Dynamic' charging nearly to degree as are the large "transfer" ports. Dynamic charging increases with the rise in volumetric efficiency at which point the larger transfer ports become more efficient.

A reduction in low in low-end power comes exactly from where John said it does, i.e., by decreased primary (crankcase) compression. However this is not the only reason for a lost in botton-end power, another is that of charge diversion, the charge that should be destined for the B.T.L. ports is diffused into the bottom window of the larger transfer port (lower, relative to the world) as would be the case for example, of a double-rod slotted engine). The larger transfer, because of its shear size and the low availability of charge mass at lower RPM is ill-equipped to handle this diversion. Or in other words, the port is simply too lazy to deal with the charge flow at low RPMs. I'm not saying it does not move fuel, for surely it does, I'm just saying it is doing so in less than an efficient manner. A manner that could be best described as a saturated port, releasing fuel of large droplet size, unlike what would be occuring through the B.T.L ports.

But once again, John is probably right, you may see an increase in top-end numbers. That would be because the charge has more availabilty to the "bottom window" of the lower transfer port when higher volumetric efficiency becomes more pronounced. Having said that, if more is available to the lower transfer, it could only be assumed that less would be available to the upper transfer. What are we to do now? Cut a third rod-slot to create a more efficient feed to the bottom window of the upper transfer? And in doing so, create an even greater reduction in primary compression. Having posed this conundrum, I will retire and let the more creative minds work out the minor details. However, please be kind enough to stay on topic.......Prof. O/B:)

[Jay Smith]

Be carefull "hogging" out rod slots out I've seen bottom end torque suffer because of created volumn produced by removing too much material...

my opinion,

[Prof. O/B]

Be carefull "hogging" out rod slots out I've seen bottom end torque suffer because of created volumn produced by removing too much material...

my opinion,

See, I got my first bite already!!! LOL............The Instigator:)

[gselite2000]

the explanations are so far over my head, and as Half Fast says, the Mercury engineers did know something about these engines, I think I will leave my block as-is.

Scott

[86vintage]

I have a 1995 steel bore that I will be putting a seven pedal front half, forged Wisecos and pinned.

John - the pistons are coming from you.
Did you get those stupid rods yet?

Does it pay to clean up the casting lines and sharp edges.
Wanted to lightly blend the castings and the sharp edges at the bore and intake port. Just do a nice clean up - not remove much material.
Match all six to be exact?
I'll be looking at those transfers tonight.
Happy New Year!
James - 86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[us1]

I have a 1995 steel bore that I will be putting a seven pedal front half, forged Wisecos and pinned.

John - the pistons are coming from you.
Did you get those stupid rods yet?

Does it pay to clean up the casting lines and sharp edges.
Wanted to lightly blend the castings and the sharp edges at the bore and intake port. Just do a nice clean up - not remove much material.
Match all six to be exact?
I'll be looking at those transfers tonight.
Happy New Year!
James - 86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif
Removing the flashing in the intake track reduces turbulence increasing air flow. On a
carb motor it help keep the fuel atomized as well. If you are talking about blending the
steel liners into the block ports you will be changing the port timing in the process. I am
out of town in Las Vegas right now so I am not sure if they came or not. I'll be back at the
shop on the 4th.

[Prof. O/B]

the explanations are so far over my head, and as Half Fast says, the Mercury engineers did know something about these engines, I think I will leave my block as-is.

Scott

Scott, I sorry I "muddied the waters" regarding your post. I wished to present a theoretical question, nothing more. Yes, you are correct, the Merc Engineers know exactly what they are doing. They wish to make a motor that produces approximately 260 H.P. The real question is whether you wish to make more H.P. As John stated earlier, the Drag Motor's expose more of the behind-the-liner ports than is done on the 260s. Increasing the flow to the B.T.L. port area, exactly as John has described would be appropriate. You aren't making that drastic of a change. If you were advancing the intake port timing you would have concerns of altering the fuel curve, etc. But you are not, just a simply flow improvement............Prof. O/B :)

[Instigator]

Was just going to post this question.

Letting a pizza get cold while I read this :cool:

So boost only huh?

Thanks Prof, gald to have you back!!

You too Mr. Marles!

Can/will either of you Wizards shed light on the "Black Art" of port roof angles/changes/effetcts from???
I'll love you for ever :)

Gary

[86vintage]

Back on the subject of rod slot width. I have a steel liner 2.5 that I am installing a 7 pedle front half. I bolted it up last night with the dowel pins in place and all the mating surfaces meet perfectly no steps - NICE!

I was going to clean up just the bottom of the rod slots. Not touch the port openings up at the exit side of the transfers. The Professors got me thinking about all that you have stated about the transfers behind the liners? Could you Plunge cut with an end mill from the reed area staight to the small transfer port? Or were you talking about something else.
I used to open the entrance to the transfers as much as possible with all the earlier porting on 2 stroke motorcycle race engines that I used to do.
The motorcycle engines never had rod slots, used to be wide open, but then again they didn't come on the pipe till about 7-8,000!

John mentioned the race blocks had wider rod slot openings - can any one give me a width dimension? My steel bore slots are aprox .980"
Looking at the Opening of the transfer ports at the bottom, looks like I can raise the opening, an easy couple of 100 thousands, to give that transfer charge a little added boost! can any one give me some good pionters in that direction as far as how much is good??http://forums.screamandfly.com/forums/images/icons/icon10.gif
Thanks,
James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[Instigator]

The Professors got me thinking about all that you have stated about the transfers behind the liners? Could you Plunge cut with an end mill from the reed area staight to the small transfer port? Or were you talking about something else.
I used to open the entrance to the transfers as much as possible with all the earlier porting on 2 stroke motorcycle race engines that I used to do.
The motorcycle engines never had rod slots, used to be wide open, but then again they didn't come on the pipe till about 7-8,000! Thanks,
James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif
And excellent questions James!

[Prof. O/B]

Back on the subject of rod slot width. I have a steel liner 2.5 that I am installing a 7 pedle front half. I bolted it up last night with the dowel pins in place and all the mating surfaces meet perfectly no steps - NICE!

I was going to clean up just the bottom of the rod slots. Not touch the port openings up at the exit side of the transfers. The Professors got me thinking about all that you have stated about the transfers behind the liners? Could you Plunge cut with an end mill from the reed area staight to the small transfer port? Or were you talking about something else.
I used to open the entrance to the transfers as much as possible with all the earlier porting on 2 stroke motorcycle race engines that I used to do.
The motorcycle engines never had rod slots, used to be wide open, but then again they didn't come on the pipe till about 7-8,000!

John mentioned the race blocks had wider rod slot openings - can any one :) give me a width dimension? My steel bore slots are aprox .980"
Looking at the Opening of the transfer ports at the bottom, looks like I can raise the opening, an easy couple of 100 thousands, to give that transfer charge a little added boost! can any one give me some good pionters in that direction as far as how much is good??http://forums.screamandfly.com/forums/images/icons/icon10.gif
Thanks,
James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif


James, just to get our jargan straight. We usually call our behind-the liners ports the "fIngers" and the "booster". We do not regard them as "Transfer Ports". This is a carry-over from the days when Merc actually had Fingers and boosters with the piston-ported motors. If you want to get technical, the correct name for B.T.L. ports would be - "Primary" the largest port, 180 deg. from the exhaust port (what we call the "booster"). The other two smaller ports would be the "secondary" (the fingers), respectively the "upper" and "lower" (that being relative to the world with a mounted motor). Yes, it is a strange world we live in. What we call the "transfers", are the largest ports, 90 deg. of, and adjacent to the exhaust port. Probably doesn't make a lick of sense to a Biker.

As you have noted, yes. The Lower "finger" port does pretty much line up with the middle of rod slot. Yes, you can shoot straight-in with an end mill to achieve better flow. Just bear in mind there are some thin spots in this area. Feel around a little, you will find them pretty easy.

Generally speaking, what most consider a rod-slot cut is to, using a vertical mill and compound angles, cutting underneath the seal ring in a diagonal manner, from approximately 1/2 way across the cylinder-floor into the corner of the rod slot where the "booster" port is located. I personally perfer not to run-out as far to the center of the cylinder floor as most, it's a waste of, and mis-direction of the charge flow and you are futher decreasing crankcase compression.

As far as the "top" of the lower windows of the transfer ports, on a Drag motor, they are approximately 4-1/32" from the top of the deck. On the "top" of the window in front of the B.T.L. ports, they are approximately 4-9/16". You can cut them with the sleeves "in", but it is very difficult (as in impossible) to recreate the bevels that exist on the back side of the sleeve. None-the-less, raising them will increase charging.

I have no problem with you widening the lower transfer port windows. But you should not do so where the "tabs" at the bottom of the sleeves line-up with the tabs on the piston. The problem with that is you are obviously "under-mining" the surface where the piston tabs must run on. If you do that, more of the thrust of the piston is placed-up on a higher point on the piston. That point being, the span between the tabs on the intake side of the piston. That's not good, because you are effectively making the piston try to control thrust at a higher point up on the piston. The skirts of the 2.5 LTR are already to short. Remember, that the stroke on the 2.0 Ltr, 2.4 Ltr and the 2.5 Ltr are the same. Bore diameter is increasing, skirt length is not. As you look at one of your Bike pistons, and compare the bore diameter to the length of the skirt, you are going to find the relationship very skewed on an outboard. This is the primary reason we have to run such sloppy piston to bore clearance on our outboards when compared to bikes. The drag blocks use a bigger end mill at the crankcase half, I' don't remember what size it is, I never left one at that size long enough to measure it...................Prof. O/B :)

[86vintage]

Profesor,
Have you ever heard of Kevin Cameron. I have been porting motorcycles since I was 14 Oh that was 34 years ago. Man I hate to date myself. Had the pleasure of having a Superflow 110 and a Dynojet Dynometer. I specialised in the 4 stroke - 4 valve heads on 750 and 1100 cc Superbikes. But I started on 125cc motorcross bikes, then build many fully ported Yamaha 350 and 400cc 2 stroke twin cylinders and my street bike bike at 19 was a three cylinder suzuki GT-750 (Waterbuffalo) that I ported, milled heads, enlarged intakes and installed larger Mikuni carbs, with three expansion chambers. Man you would have liked the sound of that at 11,000 redline.
I have build 100s of race engines and have held a number of championships for myself and for other drivers. Well now I retired from building motorcycle engines proff. 10 years ago and now work in R&D for the Medical Industry. I found speedboating 4 years ago and learned to fine tune 115 hp inlines. Was encoraged to move on to the V-6 due to there great potential of increased HP. Last year got a 1995 2.5 EFI steel sleeved motor fresh water, nice clean motor. Last year the only Mod I did was a Bracato SVS, steamwheel and EGT. Had a great year living most its life at 6,000 rpm on my 16.5 Chris Craft Caper. Had fun trying to hang on to that thing at 70 mph. Since then I have got two more 2.5 steel sleeve motors I am building. One I have got a 7 pedle front half and I am building a super light 17 foot Sidewinder with a pad and some other mods like making it center console, some airo work like the Allison's. This fall I attended the CT River run and hung out and watched a built 2.5 making passes and swaping props and the crackle of that motor and the sound of that boat at speed had me hooked! So hear I am rambling on about my new addictionhttp://forums.screamandfly.com/forums/images/icons/icon10.gif. And yes I understood and apreciated all that you spoke of, in regards to the primary and boost ports.
Take care,
James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[Tom Foley]

Does anyone have any decent photos of modified rod slot areas from their blocks ?

[86vintage]

I typed in "rod slots" and found some - I need to get to work now otherwise I would find them for you. But in your search and reading you will learn alot!
Good luck!

James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[Tom Foley]

Profesor,
Have you ever heard of Kevin Cameron. I have been porting motorcycles since I was 14 Oh that was 34 years ago. Man I hate to date myself. Had the pleasure of having a Superflow 110 and a Dynojet Dynometer. I specialised in the 4 stroke - 4 valve heads on 750 and 1100 cc Superbikes. But I started on 125cc motorcross bikes, then build many fully ported Yamaha 350 and 400cc 2 stroke twin cylinders and my street bike bike at 19 was a three cylinder suzuki GT-750 (Waterbuffalo) that I ported, milled heads, enlarged intakes and installed larger Mikuni carbs, with three expansion chambers. Man you would have liked the sound of that at 11,000 redline.
I have build 100s of race engines and have held a number of championships for myself and for other drivers. Well now I retired from building motorcycle engines proff. 10 years ago and now work in R&D for the Medical Industry. I found speedboating 4 years ago and learned to fine tune 115 hp inlines. Was encoraged to move on to the V-6 due to there great potential of increased HP. Last year got a 1995 2.5 EFI steel sleeved motor fresh water, nice clean motor. Last year the only Mod I did was a Bracato SVS, steamwheel and EGT. Had a great year living most its life at 6,000 rpm on my 16.5 Chris Craft Caper. Had fun trying to hang on to that thing at 70 mph. Since then I have got two more 2.5 steel sleeve motors I am building. One I have got a 7 pedle front half and I am building a super light 17 foot Sidewinder with a pad and some other mods like making it center console, some airo work like the Allison's. This fall I attended the CT River run and hung out and watched a built 2.5 making passes and swaping props and the crackle of that motor and the sound of that boat at speed had me hooked! So hear I am rambling on about my new addictionhttp://forums.screamandfly.com/forums/images/icons/icon10.gif. And yes I understood and apreciated all that you spoke of, in regards to the primary and boost ports.
Take care,
James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif
I remember Kevin as I purchased some cranks for my 76 RD - 400 when I worked at Orient Express Motorcycles in Freeport , NY . Kevin was writing for Cycle magazine at the time and Water Buffalos were running 180 mph on the banking at Daytona ! I used to tune many street GT - 750 's as wellas gt 550's , 350 's , etc , The Suzuki had more room for improvement due to the angled cylinder placement and consequent larger transfer area (over the Kawasaki's ) sure do miss street legal fast two strokes ! (RZ -500 Gamma )

[Prof. O/B]

I remember Kevin as I purchased some cranks for my 76 RD - 400 when I worked at Orient Express Motorcycles in Freeport , NY . Kevin was writing for Cycle magazine at the time and Water Buffalos were running 180 mph on the banking at Daytona ! I used to tune many street GT - 750 's as wellas gt 550's , 350 's , etc , The Suzuki had more room for improvement due to the angled cylinder placement and consequent larger transfer area (over the Kawasaki's ) sure do miss street legal fast two strokes ! (RZ -500 Gamma )


It is apparent that Kevin in now too old to be "trainable" in his new found love of outboard engines.:) Ha! Ha! Perhaps there may be a few burning embers left from his "glory days". That's about the only thing that ever really scared me in this business, someone who had "good fundamental 2-stroke knowledge" becoming a competitor. So all effort should be made to discourage the ole fella from any future endeavers. :) ....Prof. O.B

[86vintage]

No Kevin is some one I look up to very much and has quided me over the years when needed. Enjoy reading his monthly articles in Cycle World.
Your knowledge reminds me of him. He has a similar character of not giving you the straight answer but guides you in the right direction to form your own ideas and direction.
No you dont have to worry about me competing in the marina race engine world. I had many years in the race engines business. My carreer path has changed. And now I can enjoy the self satisifying challenge of building motors for myself again, to Satisfy that need for speed!! http://forums.screamandfly.com/forums/images/icons/icon10.gif
I was rambling on last night about the sound of a 2.5 on a STV doing passes. That brought back love of a fine tuned rocket ships.
Can't afford those tickets on the street anymore. So the way I look at it is High performance boating is the best way to go fast and not end up in JAIL!
Take care,

James
86vintage http://forums.screamandfly.com/forums/images/icons/icon14.gif

[86vintage]

Skip from Orient EX bought my Dynojet Dyno and sold it to someone in England?? 11 years ago. Skip took the retail business of Orient EX over just before I was getting out of the Motorcycle Business. The Orient Express team always took good care of mehttp://forums.screamandfly.com/forums/images/icons/icon14.gif, good people. I forgot the original owners name, he had a good reputation of building some real fast motors!
Ok back to Rod slots and Primary and Secondary ports!
I see the need to remove just the right metal from the right spot, so I don't loose to much of that crankcase compression.
Oh yes the BLACK ART of knowing were to remove just the right amount of material so the engine doesn't fall flat on its facehttp://forums.screamandfly.com/forums/images/icons/icon9.gif.
Take care,

James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[Tom Foley]

Skip from Orient EX bought my Dynojet Dyno and sold it to someone in England?? 11 years ago. Skip took the retail business of Orient EX over just before I was getting out of the Motorcycle Business. The Orient Express team always took good care of mehttp://forums.screamandfly.com/forums/images/icons/icon14.gif, good people. I forgot the original owners name, he had a good reputation of building some real fast motors!
Ok back to Rod slots and Primary and Secondary ports!
I see the need to remove just the right metal from the right spot, so I don't loose to much of that crankcase compression.
Oh yes the BLACK ART of knowing were to remove just the right amount of material so the engine doesn't fall flat on its facehttp://forums.screamandfly.com/forums/images/icons/icon9.gif.
Take care,

James
86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif
The original owners names were Jack O'Malley and Steve Bearman . I left in 83' after being service manager of the Hempstead store. Jack died a few years ago of a heart attack in the shop . I learned a lot there and met some lifelong friends including George Babor of BPM Racing engines who resides in Fl . He actually built most of the engines at the time I was there . Sorry for the thread diversion !

[86vintage]

sorry to hear about Jack. I'll send you a line tonight.
James
86vintage