Go Back  RCU Forums > RC Boats > Speed - RC Nitro Boats
Reload this Page >

Con Rod ID please. K&B 3.5 outboard

Notices
Speed - RC Nitro Boats For all your rc nitro fuel burning boating needs.

Con Rod ID please. K&B 3.5 outboard

Old 08-19-2007, 05:51 PM
  #1  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default Con Rod ID please. K&B 3.5 outboard

I have 5 con rods and 4 of them are different one is not in the picture. I'm pretty sure two types are K&B but I'm not sure about the others. Any help on what they are would be great! Who made them, and about how old they could be.

The one picture has 4 from left to right, two say K&B right on the rod and look to be cast. The next is an I beam shape. The third is what I believe to be the round K&B one.

The last one is in my engine and I don't have a picture. It's a rectangle, and the corners are chamfered. They look to be that way from the manufacture.

Thanks
Attached Thumbnails Click image for larger version

Name:	Yw67647.jpg
Views:	35
Size:	74.4 KB
ID:	745293  
Old 08-19-2007, 10:36 PM
  #2  
Ron Olson
My Feedback: (1)
 
Ron Olson's Avatar
 
Join Date: May 2002
Location: Kalamazoo, MI
Posts: 18,688
Likes: 0
Received 20 Likes on 17 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

All of them appear to be K&B rods but one might be an RPM as they used to make replacement con rod's for the K&B's.
Old 08-19-2007, 11:25 PM
  #3  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Any Idea which is the newest, or strongest? I"ve been told it's the round one, but it looks to be the smallest of the bunch, so it hat be confused.
Old 08-19-2007, 11:33 PM
  #4  
Ron Olson
My Feedback: (1)
 
Ron Olson's Avatar
 
Join Date: May 2002
Location: Kalamazoo, MI
Posts: 18,688
Likes: 0
Received 20 Likes on 17 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

A lot of people like the tubular one but they all look strong to me.
The engines have evolved over the years. I found this out with my K&B 7.5 OB's as the cases and strokes were different between models.
What we need is a real K&B expert in here to help you out some more.
Old 08-19-2007, 11:57 PM
  #5  
topfuel4430
Senior Member
 
Join Date: Nov 2005
Location: Decatur , GA
Posts: 259
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

The two on the left are the oldest, the round one on the right is the second oldest, and the "I" beam or "H" beam rod is the newest. Ive had the most success with the round rods, but the "H" beam work well also.

~James
Old 08-19-2007, 11:59 PM
  #6  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Thanks yet again James!

any clue about the rectangular one with the corners slightly chamferd at 45deg. (looks like it's factory done) (not pictured) ?

One other question while I'm at it. A parts engine I have has a cyl. head for the short glow plug, and the bowl is a hemispherical shape. Then I have two other heads both for the longer plug, and both have a second smaller hemispherical cut deeper not much bigger than the plug. Any Idea which is better, or are they about the same?
Old 08-20-2007, 12:19 AM
  #7  
jetpack
My Feedback: (1)
 
jetpack's Avatar
 
Join Date: Oct 2002
Location: Hobart, IN
Posts: 2,477
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Head Buttons: The single chamber is for high nitro/low compression setups, the other is a double-bubble for high compression/lower nitro setups is what I have been told. OPS engines of Italy was similar with their head button designs and would supply the US market (which is nitro hungry) with the large, single-dome head button and its European (mostly straight alky based) with the double-bubble head. The double bubble head should have a larger squish band area than the hemi head.

Con-Rods: I have come across three types - The cast which is actually forged aluminum and has the K/B logo on it, the other is machined aluminum - very simple flat beam type with tool marks, no chamfers and the last is the tubular rod which I think is aluminum but could be titanium - it is VERY light and strong but I have had them fold at the big end and loose bushings. There was an aftermarket company called "RPM" which produced very good rods that were similar to the flat beam style, but think they were chamfered along the sides to decrease its air drag and carried no logo.
Old 08-20-2007, 05:00 AM
  #8  
topfuel4430
Senior Member
 
Join Date: Nov 2005
Location: Decatur , GA
Posts: 259
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Hi, the single bubble head came on the earlier model 8935 and 8906 engines. The volume of that head is around .18-.20cc. The double bubble heads were the latest version from K&B and mostly came on the newer 8907, although there were a few overlap years, where you might have found just about anything on a given motor. These overlap or transition years make it very difficult to keep up with what was what on the engines as they came from the factory.

Basically, the double bubble head button is worthless. Way too much volume, even with lower nitro. The burn pattern with that head is not centered, nor as compact as it should be. The burn pattern, shape, and volume of the older, single bubble head is MUCH better.

I agree with Jetpack, it sounds like the rod not picture could be a RPM rod. They are good also, but are no longer made. If you have the option, I would run the RPM rod first, then the Round rond, then the I beam rod. The casted rods dont hold up well, but do provide nice aluminum chunks throughout the motor when they come apart.

Hope this helps, ~James
Old 08-20-2007, 09:19 AM
  #9  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

That helps a ton! thanks James and Jetpack! Next time I open back up my one engine I'll get a picture of the rod to see if you guys think it's an RPM.

The engine with the single bubble head and the rod in question is new (to me. cyl appears to have very little if no run time). It had a gold flywheel and carb on it and the previous owner did say he took the SS air cooled head off it. Funny part is it came with the SX style muffler. Sounds like I got a frankenstein engine. Would it be worth it to put on the SX style head?

Thanks again
Ken
Old 08-20-2007, 09:48 AM
  #10  
topfuel4430
Senior Member
 
Join Date: Nov 2005
Location: Decatur , GA
Posts: 259
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Hi Ken, plenty of guys are succesful with air cooled heads. I personally have never liked them, except on a MAC engine. The SS and SX heads are identical, except for the color of anodizing.

You could always try it and see what you think. Be careful not to overheat it. With an aircooled head, they like to run rich first, then after a lap or two they will lean down where they need to be when they get heat in the engine. The line of hot enough and too hot, is too thin for my liking, and thus the reason I prefer water cooling, as I can control the amount of flow. If you want a turo cut head, such as the SS or SX style head, I would recommend getting Keeley turbo head for the K&B. They work great, and are used in conjustion with the water cooled water jacket.

~James
Old 08-20-2007, 07:59 PM
  #11  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

I've heard of the Keeley turbo head before, but in my searching I have not found a source. Does anyone know where I can still pick one up?
Old 09-02-2007, 04:51 PM
  #12  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Ok, so here is a pic of the last unidentified K&B 3.5 con rod. Is it a RPM rod? thanks

sorry pics are blury, it's hard getting a good pic up close.
Attached Thumbnails Click image for larger version

Name:	Wu59674.jpg
Views:	23
Size:	161.2 KB
ID:	755361   Click image for larger version

Name:	Cx76626.jpg
Views:	19
Size:	159.5 KB
ID:	755362  
Old 09-02-2007, 07:00 PM
  #13  
jetpack
My Feedback: (1)
 
jetpack's Avatar
 
Join Date: Oct 2002
Location: Hobart, IN
Posts: 2,477
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Here's the three that I have in my stash, all are K&B. Try and compare it to the machined one of the group?
Attached Thumbnails Click image for larger version

Name:	Pn38055.jpg
Views:	25
Size:	56.9 KB
ID:	755449  
Old 09-02-2007, 10:35 PM
  #14  
RaysonCraft
Member
Thread Starter
 
Join Date: Nov 2005
Location: Washington Terrace, UT
Posts: 56
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Thanks for the picture jetpack,

The round one is easy, so is the one with the raised K&B on it. your other one has squared off edges, where the one I tried to get a picture of has 45 deg chamfers on all the corners, once again, they are way to smooth and nice to be from someone doing it, it's got to be factory.

The picture is so bad at showing it. It makes the sides look almost square, but the 45 deg chamfers almost meet on the thin edge (hope that made sence).
Old 09-07-2007, 04:59 PM
  #15  
moparbarn
 
Join Date: May 2007
Location: winchester, va. VA
Posts: 176
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

your rod still in the motor sounds like a rpm rod to me, from the description. i was finally able to buy one in the original, sealed package, so i FINALLY know what they look like. when i bought that one, i discovered i had been GIVEN one by a friend getting rid of his k&b stuff. the I or H beam rod has not given me any good service. i can count the life in runs one 1 hand. the very light/flimsy rod is my favorite. high nitro, turbo cut cranks&heads, no cooling, small props/high rpms don't seem to bother it. i'm still running the first USED one i tried. so far, i can't hurt it. i'll bet it's been in 5 or 6 engines this year. and i like to run the pee out of them[>:]. i'm saving the rpm rods until after my experiments, and settle on next year's racing setup. from everything i hear, they are supposed to be the best. if not, i have about 6 of the round ones-i'll get by.
Old 09-08-2007, 01:09 AM
  #16  
jetpack
My Feedback: (1)
 
jetpack's Avatar
 
Join Date: Oct 2002
Location: Hobart, IN
Posts: 2,477
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

Mopar, which one are you calling the light one you like? Is that the round tubular one or the flat machined one thats in the pic i posted?
Old 09-08-2007, 09:52 AM
  #17  
moparbarn
 
Join Date: May 2007
Location: winchester, va. VA
Posts: 176
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

the one in the middle. the round/tubular one. looks all weak and spindly, but lasts and runs better than any other stock rod. guess it just doesn't have enough weight to create centrifical force strong enough to hurt it?
have you weighed the rods? i'll have to get out the reloading scale tonite.
Old 09-08-2007, 10:09 AM
  #18  
jetpack
My Feedback: (1)
 
jetpack's Avatar
 
Join Date: Oct 2002
Location: Hobart, IN
Posts: 2,477
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Con Rod ID please. K&B 3.5 outboard

I suspected that but wasn't sure.

I haven't weighed one but I can tell you the only one I've been able to BEND (should have exploded!) is the one where I lost radio power (due to a cracked battery tray) and my boat hit the bank and flipped on its back, leaned out and made a 10 second peak rpm shreek until the bottom end folded over lost its bushing. They really ARE light though - almost seem hollow. I got curious one day to see if they are, and took my bent one and tried to cut it with a file, and the file said NO WAY. Very hard stuff for its weight. After I realized it was that hard I gave up and considered it to be solid titanium.

Attached Thumbnails Click image for larger version

Name:	Rp42111.jpg
Views:	29
Size:	149.6 KB
ID:	758913  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Manage Preferences - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.