Author Topic: Model 21 Briggs AP Class  (Read 4656 times)

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Offline Honda92

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Model 21 Briggs AP Class
« on: August 30, 2016, 08:38:18 pm »
Has anyone on here been running the 21 cube ohv briggs in the ap class? And if so, how have have they been holding up?

I've been reading a few past threads about them and the possibilities, but there hasn't seemed to be much said about them on here lately. Has there been a billet rod developed for these?

Offline birdman_express

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Re: Model 21 Briggs AP Class
« Reply #1 on: August 30, 2016, 11:12:28 pm »
Should be the large journal and use the AVS rod.

This is taken from the ARC website:
Fits the standard Model 31 "AVS" crankshaft with the 1.498" crank pin.
It will fit the journal of both the AVS 31 and the Non-AVS OHV 31 models.
The rod is about .020" longer than stock, which should bring the piston
up to the deck height with the standard piston.

This should also be the same with the 21.
Marc Baker

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Offline Honda92

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Re: Model 21 Briggs AP Class
« Reply #2 on: August 31, 2016, 08:42:37 pm »
Thanks for the info!

So same length rod as a 31, just a shorter stoke crank

I'm looking to get the powerbuilt model 21 w/o the balance system (as opposed to the Intek) and boring and sleeving to a 31 piston size if possible.

The cam must also be the same as in the 28 and 31 ohv?

Haven't been able to get my hands on one of these motors yet to really examine them. Have just been looking at illustrated parts sheets... but hopefully soon!!

Offline Mowerpar

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Re: Model 21 Briggs AP Class
« Reply #3 on: September 20, 2016, 12:20:23 am »
stock rod is way shorter than a 28,31,33

Offline leman

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Re: Model 21 Briggs AP Class
« Reply #4 on: September 25, 2016, 09:09:42 pm »
Thanks for the info!

So same length rod as a 31, just a shorter stoke crank

I'm looking to get the powerbuilt model 21 w/o the balance system (as opposed to the Intek) and boring and sleeving to a 31 piston size if possible.

The cam must also be the same as in the 28 and 31 ohv?

Haven't been able to get my hands on one of these motors yet to really examine them. Have just been looking at illustrated parts sheets... but hopefully soon!!

Yes the cam is the same as the 28/31 ohv's.  I use the solid gear cams from the older engines in mine.  I have been running one for 3 years now with no problems (I had a few due to my own errors assembling it...)  Rocket Ron sells a kit to stroke it with a different stock crank in it.  Im up to 29.8 cubic inches with one of the kits he offers.  It is quick to say the least :)
Nick Lema
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2014... No more DNF's :D

Offline Mowerpar

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Re: Model 21 Briggs AP Class
« Reply #5 on: October 02, 2016, 09:05:11 pm »
The 28 crank does fit and ron does have a rod for it. Like anything it will ake a bit of work to make it work.  The only thing i dont like is the not so nice rod to stroke ratio.

Offline Honda92

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Re: Model 21 Briggs AP Class
« Reply #6 on: June 25, 2017, 11:59:27 pm »
Yes the cam is the same as the 28/31 ohv's.  I use the solid gear cams from the older engines in mine.  I have been running one for 3 years now with no problems (I had a few due to my own errors assembling it...)  Rocket Ron sells a kit to stroke it with a different stock crank in it.  Im up to 29.8 cubic inches with one of the kits he offers.  It is quick to say the least :)

Appreciate the info!

Quicker than the 8hp Briggs and Tecumseh flatties??


 

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