Yfz Athena 480cc

[Terse]

The BB trend has taken off and with the cost of building and tuning I thought I'd post a topic about some things to look at and watch out for when using the Athena brand 480cc kits.

First Athena uses shorter cylinders then OEM jugs. This may not be an issue when using their pistons and gaskets but needs to be taken into account none the less. Shorter cylinders affect the deck height of a motor. Deck height and piston combos have an affect on squish. Proper squish makes great power, to tight a squish makes piston to valve contact a good possibility.

Here is a random side by side of OEM and Athena 480cc jug. Notice the difference in skirt cut outs. Nothing major just a FYI.



Here is a picture of a OEM YFZ jug ('06) next to a new Athena jug. Notice how the Athena jug is shorter!



What this does is alter the cam timing to make the motor retarded to give it more top end. Big bores normally will give you a broader TQ curve and some extra HP. By retarding the timing on a BB it is a way to cheat the engine dynamic physics to gain some extra HP and TQ. Also the major thing to watch out for when using their cylinders is with after market pistons. Namely custom pistons. I believe CP shelf pistons will be this way too, but for the record this is with the Venom custom CP brand 98mm pistons. Most (if not all) custom designed piston alter the squish to achieve more HP. They tighten the squish up to improve compression with out making large domes that will interfere with flow during the cam over lap phase. Great piston designs, but they are designed with the OEM jug heights and gasket thicknesses in mind. I run a 98mm Venom piston with my 98mm Athena jug and these two items combined need a little more fore thought into the build. With Athena running shorter deck height jugs and pistons running tighter squish you MUST use thicker base gaskets to raise the deck height to achieve proper squish clearances. If not the piston will be taller at TDC the then actual deck height of the jug! Here is a picture of what I am talking about.

This picture is the Venom 98mm piston and 98mm Athena jug with OEM base gasket...



That is negative squish clearence. Meaning the piston at TDC is TALLER then the cylinder.

This picture shows a straight edge across the top of the piston at TDC. Notice how the straight edge is sitting on the outer edge of the piston and not on the cylinder deck!



That is a VERY bad thing. That will increase your compression in this case a good .5 points and lead to piston to head contact or piston to valve contact. Never a good thing. If you only had the raised compression alone, in this case it will lead to blown head gaskets.

Here is a picture of the same Venom 98mm Piston and 98mm Athena jug with a thicker then oem base gasket. Ron Woods makes thicker then OEM base gaskets. They are what I ran for my build. Notice now how the straight edge is resting on the cylinder and not on the piston.



Here it is with out the straight edge. Notice now how you can see that the piston is at TDC and NOT above the deck height of the cylinder.



For those wanting to know how to measure squish like this.... place the piston on the rod (no rings). place the base gasket on the case halves. Lower the jug over the piston. Lay a straight edge over the piston and cylinder parallel with the wrist pin to negate as much piston deflection (rock) since the rings are not installed. Slide a feeler gauge under the straight edge and the piston. Measure your given clearance and adjust if needed. If you do not have tight enough clearance use a thinner base gasket. Cometic makes thinner then OEM base gaskets. If you are to tight run a thicker base gasket. I run .027" of squish this way. Some folks run .030" of clearance. Less squish or tighter squish = more compression and power at the risk of more maintenance, More or looser squish = less compression and less likely to blow head gaskets.

Hope this helps some folks when building their BB motors.

[kb motorsports]

Thanks for sharing eric
Most guys who buy the Athena kit are on a budget and wouldn't consider the 275.00 Venom piston. The Athena kit is designed to be a simple bolt on that adds power and reliability to the YFZ. The Stock Athena piston and cylinder has been great with us and our customers... I've had mine for a long time and no sign of wear! I'm really impressed with my gains (wr crank/ athena 98mm )

The only thing I dislike about Athena is the customer service department.

Again thanks for the find--- If all goes well I may be in the market for a Venom piston if my stock athena piston lets me down anytime soon.

[Terse]

Athena piston has some great designs. 2 ring design.. 1 comp then the oil scraper rings. Nice piston top design for cross flow. Piston skirt coatings. Now it also has some disadvantages too. Most of which come with pistons that are not expensive. Everything comes down to money. Better pistons cost more money.

I referenced this with my Venom custom cut CP brand piston as that is what I am running. However I bet that all CP pistons will have tighter squish clearances built into them. A lot of people recommend CP brand pistons to customers looking for a little bit better design and the possibility of more power. I want these people to be aware of this potential component combo that will require a little bit more fore thought. I would hate to see uninformed people buy these kits and install different pistons and end up starting them up and ruining a bunch of good parts.

I did buy a off the shelf Athena 98mm big bore kit for my yfz and ran it this way for over a month. With the exact cams, carbs, intake, pipe as before with my stock bore. It pulled strong and still made good TQ. When I removed the piston and looked it and the cylinder over I saw hardly any wear and the piston looked great! The piston had minimal wrist pin journal wear and the side skirt coating was still on.

When it is all said and done how can I judge something or give my opinion of something with out actually trying it out? :)

There are better ways to make power using the 98mm Athena kits and when altering a "kit" with other components people must understand that there maybe some things they need to take into account. That is what this thread is about. I want to help share my findings so maybe somebody won't make a simple mistake that could have been avoided. These are my finding with my motor. Other people who have gone this route before have found the same things.

I will always recommend Athena brand kits, but with cliff notes with certain builds. :)

[blue fire]

Thank you tersejr
Great post, great info

[nicker71]

thanks tersejr, good info but what squish does the stock yamaha motor have?

[Terse]

thanks tersejr, good info but what squish does the stock yamaha motor have?[/b]

Not sure but if I were to guess .030"- .040"

[bbiii]

Good info Eric keep up the good work Bro....

[Extent Racing 21]

any oppinions on other things to do when installing athena on your quad, ect what size carb, +1 valves, what grind cams. Like me, i have 187+2.5 webs, if i put the Athena on, would these still be the best cams for my application? Also how much hotter does your quad now run?

[Terse]

any oppinions on other things to do when installing athena on your quad, ect what size carb, +1 valves, what grind cams. Like me, i have 187+2.5 webs, if i put the Athena on, would these still be the best cams for my application? Also how much hotter does your quad now run?[/b]

Thanks Bobby.

"Best" is a difficult word... what is best for one is not best for another.... However IMO your cam choice was good. I gained 2.5HP by boring my stock carb out to a 41.5mm so I would surmise that a larger carb on a larger cc motor would only benefit the motor. Just remember that bigger is not always better when it comes to carbs. The bigger the carb the the more HP you will get in the upper rpms with less low end and off idle punch. On big bores cam choice becomes a key role in making power. The idea is to fill the cylinder and when the inside becomes larger you may need larger carbs to fill that larger area at the same velocity. +1 valves are a give and take. If done correctly you get some decent gains in power. If done incorrectly you will loose velocity and slow up the incoming cylinder charge. SS valves can be harder on the valve train and wear guides faster, rev slower from the extra weight (doubt it is noticeable on the butt dyno) and you will need to replace the valve springs to control the heavier valves. Cost vs. gain becomes an issue on that case.

A key piece to freeing up HP is to use lighter weight parts or in the case of big bores where the piston is larger... find companies that make their BB pistons close to the same weight as OEM. That way it does not impede the motors ability to rev like stock. CP brand pistons are very good at making power and keep the motors fast rev nature.

Key things about motor building are simple....

Keep things clean. Make sure gasket surfaces are clean of oil and grease to create the best seal possible.

My motor runs very strong! I ran the Athena jug/ piston pump gas, 2.5's cams, 41.5 carb, FCI, stock valves and 9" Nmotion and now the things I change are the +1 valves and springs and the piston, and it is ALOT stronger then before! I am very happy.

[bbiii]

Eric have you put it on the Dyno yet to see what you gained from the BB kit?

[Terse]

Eric have you put it on the Dyno yet to see what you gained from the BB kit?[/b]

HaHa... you ask?! Of coarse! I put it on the Okie dyno. Problem was I had to use a old head gasket for that trip and it was leaking some oil out by the exhaust. I am tearing it down again tomorrow and installing the new (correct) gasket that came today and then taking it up to JJones so he can take it to Utah with him and run it on the KBR dyno back to back with his Should be interesting.

[bbiii]

cool can't wait to hear the result's

[Terse]

cool can't wait to hear the result's[/b]

I think we all decided to go to Okie for the 20th :) It will be back on the dyno again.

[bbiii]

Cool we will be in spot #18 behind don's shop.

[Terse]

We'll have to stop by and say HI!

Hotter now? Not really. I ran it in Okie and the temps were in the high 90*'s like 98* so I took it easy when the motor temp gets to warm. When I ran it locally on the MX track it never got above 200* motor temp. Which for my motor, stock bore or BB, is normal motor temp. (even with a leaking head gasket)

[DOZER520]

Thanks tersejr for this post! I have learned a lot from it. I am one of those guys who is looking to get all of the performance I can with a limited budget. So an Athena jug makes sense to me. I will make improvements over time to my motor - like going to a better piston so this is very helpful in my case. thanks

[mxthunder]

Dont you also have to account for the amount that the base gasket compresses when you torque down the head bolts?

[Terse]

Dont you also have to account for the amount that the base gasket compresses when you torque down the head bolts?[/b]

Yes.

[mxthunder]

Also, I guess, rod stretch, and vavle stem stretch at high RPMs

[Terse]

Also, I guess, rod stretch, and vavle stem stretch at high RPMs[/b]

Technically all of that is figured into the squish and deck height measurements. The manual I think calls for .040" and anything less then .020" will with rod stretch, gasket crush, and used parts with greater clearances will be tight enough for the piston to hit the head or valves.