Honda TRX250R Forums banner

1 - 20 of 32 Posts

·
Registered
Joined
·
63 Posts
Discussion Starter · #1 · (Edited)
Hi guys it's been a while since I last posted.
Surprisingly enough on ebay I found NOS con rod big end A-B-C bearings, washer plates and A and C pins for my 1983 CR250 crankshaft. Even found a NOS KA4 I con rod.
So I'm thinking of rebuilding my crank with these NOS parts. My big end pin is A from what the " I " stamped on the end of it tells me. So I'm guessing the bearing is A Toyo Red.
The KA4 I con rod still is too wear limit specs so shouldn't need to replace it.

My question is when my machinist presses out the A pin should it be replaced with a B pin and vice versa go to a B Toyo Blue bearing?
Another question is my 1982 spare crank has a S7 conn rod. What's the difference from the KA4 I rod?
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #2 ·
Here's the data on A B C
Thought my one mark pin was a A but maybe it's 2 marks together.
64261
Screenshot_20200718-101259_Chrome.jpg
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #3 ·
So I ended up buying a ProX 1978-2001 Cr250r connecting rod kit.
Getting It installed trued and welded next week.
64459
 

·
Registered
Joined
·
13,278 Posts
Hi guys it's been a while since I last posted.
Surprisingly enough on ebay I found NOS con rod big end A-B-C bearings, washer plates and A and C pins for my 1983 CR250 crankshaft. Even found a NOS KA4 I con rod.
So I'm thinking of rebuilding my crank with these NOS parts. My big end pin is A from what the " I " stamped on the end of it tells me. So I'm guessing the bearing is A Toyo Red.
The KA4 I con rod still is too wear limit specs so shouldn't need to replace it.

My question is when my machinist presses out the A pin should it be replaced with a B pin and vice versa go to a B Toyo Blue bearing?
Another question is my 1982 spare crank has a S7 conn rod. What's the difference from the KA4 I rod?
You really need to measure the crank pin bores of both sides of the crankshaft to determine the correct new crank pin diameter to use. The interference fit is specific, and somewhat critical to the crankshaft.

At BDT we use a Sunnen PG-800-S Gage, can read in .000050” increments, yes 50 million…a misguided member here on .NET tried to argue with me about needing a gage that can read .000050”, well you need that kind of accuracy to hold .0001” & inspect interference fits of bearings, crankshaft bore, and rebuild to OEM specifications.

Do a search on here for pictures of the BDT Sunnen Gage, and BDT crankshaft re-builds as well as how to properly inspect a new or rebuilt crankshaft between centers using three indicators.

Then double check the new pin diameter to match the correct interference fit or press fit. That is the correct way and approach that will give you a new assembly back to OEM just like Honda originally assembled the crankshaft.

To insure the pin stays secure, after the crankshaft is fully aligned back to Honda specifications using between centers and three indicators; you can TIG weld the Pin on each side by forming two small equal weld arcs approximately 120 degrees total, and perpendicular to the Pins center line…this is an option, and really not needed if the correct pin to crankshaft pin bore interference fit is adhered to.

Carlos
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #6 ·
Thanks Carlos, that good info..
If it wasn't for this Covid going on I'd have my crank delivered to you in a heart beat.
So it might be a good thing to have this ProX pin tig welded into my crank just to be secure what ever the clearances average out to.
I had a chance to buy a NOS OEM 1983 CR250R crank for $500 and it's still for sale. Decisions decisions....
Good to have a spare crank.
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #7 · (Edited)
@acecarlos
This ProX con rod kit I have I noticed the big end pin is capped off on each end. Is this for better crankcase compression?
So when I get that pin tig welded would these caps need to be welded too? I don't know how thick they are and whether their pressed in or soldered?
BTW, upon inspecting the kit I of course accidentally scattered the 16 roller bearings so without thinking I picked them up with a magnet. Not a good idea! So I had to order a demagnetizer off of Amazon, Lol.

Willard.
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #8 ·
Wow that’s a hell of a saw. Always interested in these builds although I know nothing about hot saws. Some cool stuff.
Very competitive sport, these Honda hotsaws must be in the highest state of tune. They have no cooling system and are allowed 1 minute of warmup time. They must be pulled started and be at WOT into the first cut.
To make things even more difficult three cuts must be done within 6 inches of marked off wood.
 

·
Registered
Joined
·
13,278 Posts
Competition Saws are Awesome Machines...:)

The caps do not get welded, only the pin, and it's important to TIG weld as I described to avoid distorsion and alingment issues after welding.

Carlos
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #10 ·
@acecarlos
Thanks for the info. My 1978-2001 CR250R ProX rod kit has a 59.75mm long pin. My 1983 CR250R crank is 64mm wide.
1984 and newer CR250R cranks are 60mm wide so the welding will need to be done a bit inside the pin bore on each side.
Dave Moore developed this cooling ring for welding Honda cranks.
64465
 

·
Registered
Joined
·
453 Posts
Willard, another source for a ton of information is LED performance in Gresham, Oregon. Arlan has been building hotsaw engines for years and I believe he even sponsors a few people in the sport. Give him a call and chat with him, I'm sure he could share some of his wisdom.
Loren
 
  • Like
Reactions: scrappy

·
Registered
Joined
·
13,278 Posts
Willard:

This is how it's done at BDT, ask other builders to show you their setups, then you can decide who to talk to;

Crankshaft Rebuilding at BDT Motorsports

Note on the BDT crankshaft, the added Heavy Metal, and the Balancing holes at different depths & locations at top. At BDT we truly balance our crankshafts, I am sure no one else is doing this level of re-build & balance.

When you stop at BDT, I can show you the Dynamic Balancer…

64467


64468


Carlos
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #14 ·
Willard, another source for a ton of information is LED performance in Gresham, Oregon. Arlan has been building hotsaw engines for years and I believe he even sponsors a few people in the sport. Give him a call and chat with him, I'm sure he could share some of his wisdom.
Loren
Loren, thanks for your input . I haven't spoken to Arlen but I have years of following his hotsaw builds through other competitors .
The trend with LED is building big bore Honda hotsaws which I have no interest in.
I have decided to stick with the light switch power band of a CR250 short rod 261.
Plus my YZ125 and cr250r engines is a very different concept from the norm where I converted these right hand ignition engines to run in reverse crank rotation with the engine laying horizontal with the carb up exhaust underneath. Many more benefits then the usual vertical cylinder hotsaw design has.

And for short 5 second bursts of top end power the reverse rotation actually has improvements in power and less vibration.
Even though the major piston skirt thrust is now on the hot smooth large exhaust side wall, there is very good exhaust port seal on the large area exhaust side of the piston.
The con rod angle on the downward power stroke has greater leverage rotating the crankshaft.
The straight upwards compression stroke angle produces a longer more complete bigger compression of fuel charge.
I'm on my 3rd year now of R&D on my design.
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #15 ·
Willard:

This is how it's done at BDT, ask other builders to show you their setups, then you can decide who to talk to;

Crankshaft Rebuilding at BDT Motorsports

Note on the BDT crankshaft, the added Heavy Metal, and the Balancing holes at different depths & locations at top. At BDT we truly balance our crankshafts, I am sure no one else is doing this level of re-build & balance.

When you stop at BDT, I can show you the Dynamic Balancer…

View attachment 64467

View attachment 64468

Carlos
@acecarlos , thankyou that is a wealth of good information there.
I hope to stop in your shop in the near future soon.
My '83 Honda crankshaft is a good candidate not having the tin can covering. Only 2 aluminum stuffer plates inside the webs.
Willard.
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #17 · (Edited)
64472
@acecarlos
This ProX con rod kit I bought BTW, upon inspecting the kit I of course accidentally scattered the 16 roller bearings so without thinking I picked them up with a magnet. Not a good idea! So I had to order a demagnetizer off of Amazon
So I get the demagnetizer and it got the 16 roller bearings low enough that my compass needle barely moves. The rod doesn't appear to effect the compass, same with the plate washers must be stainless steel, the top bearing even had some magnetism but the wrist pin sure does. May need to get a stronger demagnetizer.

I don't think the pocket magnet did this to the whole kit. I wonder if shipping through International customs ex rays would magnetize this kit? Or at the factory in Japan?
How big a deal is this guys? I don't want possible metal particles in the crankcase sticking to these bearings.
 

·
Registered
Joined
·
13,278 Posts
View attachment 64472
So I get the demagnetizer and it got the 16 roller bearings low enough that my compass needle barely moves. The rod doesn't appear to effect the compass, same with the plate washers must be stainless steel, the top bearing even had some magnetism but the wrist pin sure does. May need to get a stronger demagnetizer.

I don't think the pocket magnet did this to the whole kit. I wonder if shipping through International customs ex rays would magnetize this kit? Or at the factory in Japan?
How big a deal is this guys? I don't want possible metal particles in the crankcase sticking to these bearings.
"Guys"....crickets, LOL

Good catch Willard; I will bet you most builders don’t de-magnetize. I am sure the ‘boys’ at MacDizzy would agree.

At BDT we have an industrial de-magnetizer, it is somewhat of a “big deal”. Leaving magnetism on rolling elements is a “big” no-no; it will trap/catch fine metal particles & dust and increase wear noticeably.

Carlos
 

·
Registered
Joined
·
63 Posts
Discussion Starter · #20 ·
@acecarlos
My San Francisco rescheduled October trip with the family doesn't appear to be happening. Canada USA border is still closed and very little chance it will open anytime soon this year.
Yes I'd love to see your dynamic balancer in action.
 
1 - 20 of 32 Posts
Top