long rod crank in an 86 engine

louis mielke · Post by **louis mielke** » January 15th, 2011, 4:25 pm

I've search quite a bit, even drilled down through several pages of the Drive Tech section and I can't really find any info on using a spacer plate to run the newer long rod crank in an 85/86 engine.

Does anyone have an experience with this and can chime in anything I need to watch out for and be mindful of?

I have my new crank, the spacer plate and several different thinknesses of base gasket, I'm still waiting on my 86 top end to come back from newcomb.

Any advice would be appreciated. My biggest concern is that there's going to be a lot of bottom end volume that wouldn't normal exist. I'm going to match the bottom of my cylinder and the spacer plate so i don't think the flow into the transfers will be that disturbed.

Please anyone with knowledge help me out. Thanks in advance.

rsss396 · Post by **rsss396** » January 15th, 2011, 4:53 pm

If your spacer and 1 gasket equals 5mm than your port timing and cylinder head squish will not have changed.
Don't worry about the extra crankcase volumn it's no different than the 87-01 motors.
The long rod will help with piston wear

100hp honda · Post by **100hp honda** » January 15th, 2011, 6:52 pm

ya what rsss396 said.

might need to mod head stay slightly. pipe brackets may be off alittle also but maybe not enough to cause any issues. cylinder studs may be a tad short. carb/airbox alignment will slightly change. i never put a spacer on the hondas, just a few things i would double check.

louis mielke · Post by **louis mielke** » January 15th, 2011, 10:48 pm

Engine is going in this.

It's built on a 01 frame and had custom head stay brackets made.I also bought the longer studs for this build and some other odds and ends from the newer year engine to swap in. Pipe will fit fine, if not better than before. Can you spot what CR500 parts are in there? It's 60% CR500.

I'm building a dune engine and putting my MX engine on the shelf for the season.

Thanks for the replies!

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » January 16th, 2011, 6:38 am

Why not stay short rod?

louis mielke · Post by **louis mielke** » January 16th, 2011, 1:23 pm

The main thought was parts availability. I was given the impression the short rods are short on supply if not discontinued so I just bought a new crank.

If I was misinformed on that info, well then I was wrong and now my reason has become, "jes cause" that's what I bought.

I was also given the impression that long rod would smooth out power delivery and make my trike more enjoyable to ride (let snide comments commence) for longer durations. Its decent for a 4-5 laps in our outlaw class motos but on long trail rides it can feel pretty harsh by the end of the day. This engine is meant specifically for a dune trip I'm taking in feb/mar.
(yep eastcoast meets westcaost, from maryland going to the imperial sand dunes in cali)

I know in the atc250r, the long rod vs the short rod, the long rod engine just seems to have a little more punch in the bottom end compared to the short rod. It was explained to me that long rod was basically a longer lever and therefore put better leverage on the crank pin and thus created the "feeling" that th engine had a little more in the sack. Also the long rod changed the angle the force was applied to the wrist pin on the piston which caused a less harsh "push and pull" in the bore.

I'm sure someone might say its all BS but it made sense in my head so I went with it.

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » January 16th, 2011, 5:31 pm

The short rod motors rev up fast, but beyond that part. I haven't run it to see what's changed in power but the port timing is deffinately different for the two

100hp honda · Post by **100hp honda** » January 16th, 2011, 6:19 pm

with all things eqaul except the rod, i doubt theres much power difference either way. it probly does rev up alittle faster, "alittle" is the key word. cant recall anyone complain about any year cr500 motor revving slow however.

im thinking it was a longevity thing. cr500 pin is so low on the skirt, a rod with less angle puts that much less thrust in that area.

if you look at the 550 motor i think it will make sense. 82 stroke with 140mm rod. alot of angle so ktm put the wrist pin 8mm higher to lessen force against the weakest part....... the skirt.

honda basically accomplished the same thing. instead of changing pin height they lengthened the rod.

these are my ideas why. it makes perfect sense to me.

100hp honda · Post by **100hp honda** » January 16th, 2011, 6:31 pm

honda pistons crack enough as it is. imagine even more thrust load in the skirt area. would it reduce piston life by 1/2 ? 1/4 ? i dont have that answer but it sure wouldnt make things any better

http://www.youtube.com/user/500bigbore · Post by **Roostius_Maximus** » January 17th, 2011, 7:53 am

I have a bridgeless short rod motor with a vertex in it, I turn the piss out of it.
Ask Paul Stoffers what rod he prefers.
Ask Danny Graves what he thinks of them

I'm considering making the engine for my new AF short rod

Nodge · Post by **Nodge** » January 17th, 2011, 8:04 am

Love the short rod motor.
I've had 3 of them.

pstoffers · Post by **pstoffers** » January 17th, 2011, 9:11 am

To the short rod......

maddog1927 · Post by **maddog1927** » January 17th, 2011, 10:55 am

Am I correct that the short rod is no longer available, oem or aftermarket, or are they still / back in production. Just wondering.

http://www.youtube.com/user/500bigbore · January 17th, 2011, 11:17 am

they were back as part# 13200-ka5-690, it needs 2 washers 13202-ka5-741 with it

BannedCR500Riders.com

long rod crank in an 86 engine

long rod crank in an 86 engine