Author Topic: Stroker cranks and big motors for luhojs. (Read 9728 times)

Sam Green Racing · « **on:** January 14, 2011, 12:25:19 am »

Luhojs, a new member posted about a stroker motor that he was building and said he would start a thread on the build.
Member Jon Weeks posted this info in reply.

I need a lot more thinking done to the motor. I am still in the large chunks phase. The crankshaft for instance: I haven't checked what the rod angle is going to be with stock rods. I don't even know yet what rods to use. I have got no idea what he CR is going to be. I think it will clear the cylindersleeves but I haven't checked. I don't know how to compensate for the needed extra cylinder length. I could make an aluminium strokerplate from a base gasket pattern but maybe there are more elegant solutions. and so on.
I might start a new topic just to try and get some info from fellow enthusiasts

As for the head it will defeniately need a valvejob with bigger valves and of course porting. I don't know yet what the best combination with this cam is.

Big thing is I want it to be as they did it in them days. A dragbike that takes the win on sunday and you ride to work on monday..

[/quote]

Slightly off topic, but definitely in response to previous comments: Automatic cranks have the exact same stroke as the clutch versions. The primary chain changes but using gold wing clutch baskets, you can make it work. The real factory stroker crank is the '79-'82 Honda 900F. You don't want to use the '82 1100F crank due to cam chain issues. You'll gain 6mm in stroke. You can make a metal spacer for the bottom of the cylinders and use stock length rods and/or use shorter DOHC Honda 750 rods (4?mm shorter) The SOHC case must have some slight relief for the "stroker" counterweights. The ignition used is stock points plate/advancer unit from the older bike that the DOHC crank end is modified to use. Seals aren't the same for the crank ends. You'll have challenges to modify the 900F crank to kick or electric start. It's a lot easier to weld up your stock crank to increase the stroke. Ape can help with that. The torque increase in the midrange is very noticeable.
The stock rods don't break with a torque converter. Clutch SOHC 750's drag raced do break rods especially with heavier pistons (aka bigger). The shock loading of sticky rubber and grabbing clutches can break stock rods especially as you significantly increase horsepower. Hondamatics don't have as much shock loads when drag racing. The stock rods stretch with bigger, heavier pistons. The piston pins will start rattling in oval holes in the small ends of the stock rods. I've got a set that I replaced shortly before it would have put metal on metal somewhere.... The DOHC 750 Honda rods are better, but still not designed for racing.
Sam, you need to start working on your reactions - No, not catching the flask before it hits the floor! We're not trying to improve your wrist or elbow motions, but your fingers need to be on time. I'll find an online practice tree somewhere and post the url here.
I'm booking my flight this week. At least one of us is crazy here!

Hondamatic
[/quote]

And the latest offering from APE that we must not tell anyone about

http://forums.sohc4.net/index.php?topic=82261.0

Sam.

jaguar · « **Reply #1 on:** January 14, 2011, 11:06:01 am »

thought one of the reasons for using the DOHC 900 crank was the better chains?

I too am trying to learn more about stroker and big bore motors for one of my builds.

read here about using cb1100r rods once?

jweeks · « **Reply #2 on:** January 20, 2011, 12:23:02 pm »

jaguar,
Let's not mix primary and cam chains. Yes, the primary chain is very strong. To run a clutch with a Hondamatic or 900F crank, you need the early Gold Wing clutch parts to mate up with the Hondamatic primary chain.
Stroke your 750 with a 6mm increase from the 900f crank or 5mm from Ape. Various length rods will bolt to the "stroker" cranks. What budget, what rod angles, etc. will determine what you use. The cam chain changes if you use the 900f crank. Creativity will help whip up cam gears for the 900f cam chain. Either way, your midrange improves greatly!

Jon Weeks

Steel Dragon Performance · « **Reply #3 on:** January 21, 2011, 02:45:20 am »

Are the 750 twin cam cranks the same as the 900f's, other then the stroke, so that a guy can use them to fit the cases and cam chain mock up ?

jweeks · « **Reply #4 on:** January 21, 2011, 08:15:52 am »

I'd guess so. Never checked the 750 crank counterweights against the 900f ones. The clearancing of the cases for the crank might be a little different. It's just a small amount of grinding, not affecting strength significantly. Cam chain should be the same. I don't recommend the DOHC 1100f crank because it's the same stroke as the 900f, just uses a bigger, heavier cam chain.

Hondamatic

luhojs · « **Reply #5 on:** January 22, 2011, 08:29:59 am »

First off: thanks to SamCB750A for starting this topic.

I was wondering if there is choices in the stroke. I have seen 5mm and I believe also 6mm. Obviously there is a a limit where the crank runs out of flesh. How much would that be?
The other thing I like to know more about is how the increased rod angle has an effect on piston life. Sinde the rod angle increases I presume the force on the load side of the piston also increases which leads to accelerated wear.
This would be even more so with shorter rods to make up for the increased stroke.
Is this noticeable at all? I understand strokers are not meant to travel around the globe without an overhaul but I'd like to get some idea on the lifespan of a stroker motor.

One more thing I was wondering is how shorter rods influence the tuning. They have less "hang time" around TDC which will need different timing perhaps a different timing curve and thus a timing system capable of changing curves
Any thoughts on this?

754 · « **Reply #6 on:** January 22, 2011, 08:58:00 am »

Crank is out of flesh stock..
Welded up and remachined to accomplish the stroking. Unless you can do it with drop in reasonably priced facrtory parts, it is usually pricey..

Go to a fresh 970 or 1000cc, or get a 80 or a 100cc increase by stroking.....let your wallet decide..

JLeather · « **Reply #7 on:** January 24, 2011, 04:36:18 pm »

I believe the DOHC750 rods are only ~1.5mm shorter than a SOHC750 rod. Combined with a spacer you might be ok, although you can't get much spacer in there before you're out of slack on the cam chain.

jweeks · « **Reply #8 on:** January 25, 2011, 04:18:49 am »

Yes the side loading increases. I used stock length steel rods on my 6mm stroker (900F crank). Had a spacer made for the bottom of the sleeves. The improvement in piston rings should make several thousand miles probable, depending on how you use it. If you're racing, use a leakdown check to determine how things are sealed internally. Usually, you go with bigger bore pistons with your stroker crank. The bigger the bore, the more advance you need to give enough time for flame travel across the combustion chamber. The advance curve can be played with using a digital ignition box and your laptop. Experimenting on a dyno will fine tune your power with custom advance curve plots. Don't expect major gains there. It's called fine tuning for a reason. I picked up 4 tenths on my dragbike going to the 900F crank with my 73mm big block already there. It's mostly improvements in midrange torque that I got. Good luck with your plans!

Hondamatic
aka: Jon Weeks

jaguar · « **Reply #9 on:** January 25, 2011, 02:17:53 pm »

you used dohc or sohc rods?

Steel Dragon Performance · « **Reply #10 on:** January 25, 2011, 09:58:54 pm »

Jon , what kind of times in quarter mile with that set up ? and were to find cam sprocket and crank seals.

Steel Dragon Performance · « **Reply #11 on:** January 25, 2011, 10:09:17 pm »

Would you lighten the 900 crank to stock sohc crank weight for drag racing ?

mec · « **Reply #12 on:** January 26, 2011, 01:08:24 am »

Quote from: Steel Dragon Performance on January 25, 2011, 09:58:54 pm

and were to find cam sprocket and crank seals.

this could help:
http://forums.sohc4.net/index.php?topic=54803.0

mec

jweeks · « **Reply #13 on:** January 26, 2011, 06:32:49 am »

I'm surprised at the interest! SOHC stock length aftermarket steel rods. I've had it on a chassis dyno once before the rings had seated. I run the F head with some very good porting. 34mm CV carbs. No, I didn't extensively lighten the 900F crank. From the charts, it's around 1180cc. Motor was built for Hondamatic bracket racing. I must have midrange torque when drag racing a 2 gear bike. It made 99 horsepower at the rear wheel at 7,500 rpm and 98 horses at 10,500 rpm. Remember that the torque converter eats a lot of horsepower. 20% would be a good guestimate of the converter loss. It runs high 10's in the quarter at 124 mph. Drag chassis with fiberglass body. About 620 lbs with me on it.
Seals for the 900F crank were easy. Use the seals that fit the crank in the 900F! The 750A seals give you an oil leak on the ignition end.
Cam gears were made up of SOHC cam gear centers and the outer toothed section of the 900F cam gear. Four spot welds to hold it together without distorting it much. Reading the articles on how others have done it shows that they didn't realize that you can get cam chains in multiple lengths without a master link. That's what I did with mine. Used a cut stock chain to determine how many links that I needed for the motor and ordered it.
Challenges are fitting correct cam chain and primary chain tensioners. You will have to do some machining/fitting to make anything work correctly. Hope this helps!

Hondamatic

Steel Dragon Performance · « **Reply #14 on:** January 26, 2011, 05:10:37 pm »

Thanks guys for the advice and info. Sounds like it could be a really fun project to do.

JLeather · « **Reply #15 on:** January 26, 2011, 06:57:29 pm »

I'm curious about these longer one-piece cam chains. Any more info on where to come up with those? I wanna run some CB900 rods in my next 836 with a base spacer.

MRieck · « **Reply #16 on:** January 26, 2011, 07:55:52 pm »

Quote from: JLeather on January 26, 2011, 06:57:29 pm

I'm curious about these longer one-piece cam chains. Any more info on where to come up with those? I wanna run some CB900 rods in my next 836 with a base spacer.

DID will make those I figure.

jweeks · « **Reply #17 on:** January 27, 2011, 05:19:35 am »

Mike's right. DID makes 412 style cam chains that fit the 900F. That chain also fit many other bikes and ATV's. You can get just about any reasonable length in 2 link increments. (ie: 88 links, 90 links, 92 links, etc). Major bike parts suppliers should be able to help you.

One other thought for the big displacement strokes - The 900F crank is 6mm more. It can be rewelded and reground for more stroke just like what APE did with the cb750 cranks. My 6mm increase isn't the limit of the cases. Just a thought for those who want a lot of torque....

Jon Weeks

bear · « **Reply #18 on:** January 30, 2011, 01:52:10 pm »

Working with a dodgy memory I think we used a cam sprocket from a CB250N.
A cam adjuster from a YZ400F.
And the barrels where sand cast for us by an old bloke some years ago.
We have two motors one is is rated at 124rwhp, the other at 135rwhp.

Cheers,
Brian

bear · « **Reply #19 on:** January 30, 2011, 01:58:01 pm »

Not real good at posting pics, here's more (I hope)
Cheers,
Brian

jaguar · « **Reply #20 on:** January 30, 2011, 04:53:26 pm »

bear
that was in a bored and stroked SOHC4?

any more info in the build?
what did you run for rods and pistons?

bear · « **Reply #21 on:** January 30, 2011, 09:11:55 pm »

Quote from: jaguar on January 30, 2011, 04:53:26 pm

bear
that was in a bored and stroked SOHC4?

any more info in the build?
what did you run for rods and pistons?

Yep.
DOHC 1100 rods first up and Carrillo's now.
We had some issues with fatigue with the Honda units, but I don't think that would be a problem normally.
XR250R pistons in our big motor and RC45 pistons in the small motor.

Cheers,
Brian

bear · « **Reply #22 on:** February 01, 2011, 04:43:51 pm »

We are pulling the little motor tonight.
Need to replace a couple of bent shift forks.
The old girl is starting to breath a little heavy, she was pumping a good 300 to 400ml into the breather tank at the Island.
No complaints though, two seasons without any major issues is pretty good

If anybody's interested I will have a crack at posting pics.
Should I start a new thread Sammy?

Cheers,
Brian

Steel Dragon Performance · « **Reply #23 on:** February 01, 2011, 05:07:30 pm »

I would like to see inside. You had to do some machine work on the pistons ?

JLeather · « **Reply #24 on:** February 02, 2011, 04:43:32 am »

I'm definitely interested in the tear-down and rebuild pics too. One of these days I gotta do a really big NA motor

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Author Topic: Stroker cranks and big motors for luhojs. (Read 9728 times)