right opening-rpm of clutch, red spring

[jaki]

Hello,

I changed the engine of my max II from 425ccm 16Hp Tecumseh to 993ccm 35Hp Briggs. Both 4Stroke nearly same rpm max.

both belt pulleys are from the old engine. Original springs in them.

The new engine makes 3600rpm max. Then the max goes about 45mph.

The cluch is from the 1980s. I think Salisbury 770 clutch. The engraved text says 5000rpm max, but not at wich rpm it is fully engaged! if you look at the clutch when you give throttle it is fully engaged before the engine turns ist max. rpm.

My problem:

When im driving and start accelerating the engine first revs up and then the Max starts to get faster till it reaches top speed. If i then hit lose ground (plowed field) the rpm stays the same but the clutch goes back to slower translation/Speed but the engine has still lots of power. I can hit max rpm of engine but the Max won´t reach more Speed than about 15mph due too the not fully engaged clutch on crankshaft.

My question:
would the "legendary" red spring make my performance better? Would not rev the engine so high to get fast in rough terrain. It has enough tourque but i can´t use it...
is the red spring softer?

Clutches are lined up correctly and lenght of belt is also right.

Does anybody know when These old clutches are fully engaged? New clutches on new Max II are fully opened at 1700 says the Internet.

Would be very Kind if anybody can give me some tips,

Thanks, Jakob

[hydromike]

Jakob, the very first thing I'd look at is the drive clutch. Remove it from the engine and take it apart completely to check for broken springs and the condition of the roller weights. Too often, these clutches see decades of duty without ever being cleaned, service or repaired. It's not uncommon at all to have one or more broken springs and have rollers that are either flat sided, or bushings so worn that they won't budge. A 770 (or 780) series clutch is only held on to your crankshaft with a 1/4" keyway after removing the bolt holding it on. It'll slide off, even if it takes a bit of persuasion. After that, remove the three bolts that hold the cover on. Nothing is under tension at this point, so you can do this safely and easily.

This is a first critical step before you go putting a red spring band-aid on the problem. That could actually make your situation much worse if the drive clutch isn't operating at peak efficiency...

Let us know what you find out...

::EDIT:: I could have answered a couple more questions. The red spring is a bit stronger, meaning that it resists being twisted and compressed in the secondary (driven) clutch a bit longer. The idea is that in some heavier machines, the engine rpm must be higher to engage the spring, meaning that the engine is making a bit more power at lower vehicle speeds. When you drive through loose, more resistant terrain (mud, loose soil, or up a hill) the secondary clutch "downshifts" more quickly with the red spring than with the stock (usually green) spring. The engine rpm actually increases since the gear ratio has increased. This is helpful on heavy machines that are making less power (maybe a 16hp Max IV loaded down or a Super Swamp Fox, for example). With a 35hp Max II (), I doubt you'd gain a lot with a red spring whether or not your drive clutch is working correctly. I run the red spring on two heavier machines (the Swamp Fox and a 980 Hustler) because they're heavy and use 26" tires.

The 1700rpm speed you're quoting is when the clutch STARTS to engage, not full engagement. This is to allow the engine to make some power before it's under load. The full engagement is going to depend on the load the engine is seeing, but in all of my experience with big fat 4-stroke machines, the stock 780 drive clutch (when in good working condition) is all I've ever needed in the most difficult terrain.

When it comes to tuning the two stroke clutches though... I gotta guy.

[jaki]

The 35hp feel very good in the light Max, thats true
But can´t bring all the tourque and power to the wheels now...

How Long do your belts last normally? got 20hrs on the first one till it fell apart. Most time driving on hard gravel and loose soil.

The ATV got completely rebuild last Year june. Had every thing apart, even Transmission.
I opened the clutch like you said. can´t find broken springs. I lifted up the three arms with the rolls on them one by one and checked the rolls for theire clearance. They turned freely and had not much play.
Can´t find any damaged or wornout parts.

I´m now thinking of changeing to softer springs. Maybe I can add some extra weights to the arms...
Anyone has done that bevore?

greetings from Austria,
Jakob

PS: pictures of the complete rebuild in the gallery

[ARGOJIM]

If this engine is mounted, here is the problem.

[Nubs]

Off by a mile if it is..

[Toys4Me]

Belt also looks a little narrow.

[jaki]

@ ARGOJIM
Do you mean the engine is to big and to strong for that belt-clutch setup?

@ Toys4Me
If the clutch on the engine is on ist "fastes" Position, the clutch on the T-20 is fully engaged. If I put a longer belt in, it would not open the front clutch complete.

I used a 28x9mm belt. I think a 30x10 would also fit. I tested that by holding it to the transmission-pulley in ist closed Position.

The fist belt fell into thousands of pieces after 20hrs

[wfo]

it looks as though the clutches are misaligned causing the belt to twist. and set up should be with an 1.25 wide belt with that h.p.

[ARGOJIM]

WFO the clutches pictured probably require the 1-3/16" belt. Which looks to be 30mm.

Jaki, look at picture and then check yours, a simple check would be to lay a straight edge in the driven with out the belt and it should end up just off center of drive clutch.

[jaki]

I lined up the engine to the transmission like in the manual, which says the same like your picture. I had the engine and belt running to controll if ist really straight.
The line up of the clutches is not the problem!

Is the belt to small to transfer 35hp from the engine to the transmission?
What Hp do you run on this belt size and how long do they last?


I even tought of a harder spring for the clutch on the transmission to get more pressure to the sides of the belt. With this setup, i think the clutch on the engine will engage to top Speed at higher rpm due to more resistance to open the transmission-clutch.
Maybe need then to upgrade the engine clutch to a lower rpm setup?



IMG_2843.jpg

[Toys4Me]

I've always ran 1.25" wide belts. Are you sure the belt tension is correct? If the belt is to loose the clutches wont operate correctly.

[ARGOJIM]

I'd suggest getting a belt sent over there from Max, yes it's costly but gives you proper sizing to find locally later.
Noticed you belt was 28mm which looks to need to be 30mm, also looks to be 9mm and that looks to need be in the 15-22mm range from what is listed for various belts, then of course the length needs to be proper for where you engine sits or engine set to where belt fits.
The thickness and taper of the belt are clutch specific for proper engagement, so with a narrow/thin/improper angled belt you'll get improper action and short life span of the belt as well as possibly grooving the clutches from accelerated wear.

If you could find a listing for a factory replacement with the mm's listed you could always source it locally.