Timing Chain fit issues

Hello all. Have a little dilema here. I have a 2000 FC 501 Berg which I have not yet ridden(AUHHHHG that hurts, bought it back in November 2002). Seems that the people I got it from rebuilt the motor and when I recieved it there was no Spark. After some used ignition modules did not fix it and then a new module that lasted two seconds I replaced both the module and stator to get the fire. After firing up the bike it ran for three minutes and while idling she decided to threw a big flame out the pipe. The timing chain snapped. Apparently a nut fell off the auto-decompession lever. I had a professional mechanic take her down and when reassembling he can not get the right timing chain tension. Seems that with all the stock parts the chain is way too tight. When adding a link the tensioner does not have enough to firm her up enough. He even tried an earlier tensioner to no avail. (I am thinking the tension is what may have caused the chain to break in the first place). Anyhow hoping to pick some brains from what seems to be a wealth of a knowledge base. Thanks

John B

Hi John,
Somewhere around 1997 Husaberg deleted the cylinder base gasket and increased the main case cylinder base height in order to maintain the same deck clearnace. Since the engine had been rebuilt by ATK prior to your receipt it is indeed possible that you have a mismatch of parts. (If I recall Frank White did have Husaberg inventory spanning several model years)

If you do have a base gasket installed remove it. This alone should net you the proper chain slack. If no base gasket is found simply have .020" - .040" turned from the cylinder base.

Upon reassembly confirm your cam timing and insure proper valve to piston clearance exists.

Hope this helps.
Kindest Regards,
Dale

Thanks Dale. If this is the case should the increase in compression be any concern? The scoot seams to be a pretty high compression to begin with.

buckwheat said:

Thanks Dale. If this is the case should the increase in compression be any concern? The scoot seams to be a pretty high compression to begin with.

Click to expand...

Compression ratio should prove of little concern with a mere reduction of .020" - .050" in cylinder height. Any increased detonation sensitivity from the compression increase will be more than offset by the redcuction in squish clearnace.

Piston @ TDC should be flush with the cylinder top. Such will provide an installed deck clearance of roughly .050".

Kind Regards,
Dale

...squish clearnace.

Please explain.

By removing the base gasket wouldn't this result in the piston traveling further up the cylinder thereby decreasing squish clearance (the gap between the piston and head at top dead centre)?
:?

removing the base gasket does increase the compression by a very small amount. you will be well below the quoted figures at present and by removing the base gasket you will be getting to the factory figures and it should be of no concern.

what is squish? it is a ring around the outside of the combustion area whereby the manufacturers try to get the piston to come up and go flush to the head. by having this all the way around the outside and say 8mm wide you actually make the combustion flame happen on top and in the middle 80mm of say a 100mm piston.

this fools the combustion into finishing more quickly in a small area and therefore we don't need as much ignition advance. i'm sure you knew that a small combustion chamber is more efficient than a big cylinder. squish has to be as small as is safe to work but if it's more than 1mm when running then it starts to be ineffective. it needs to be around .040" = 1mm.

recently in a lost post i mentioned how good the factory squish was because i could still read the digital code for the piston that was printed in ink in the squish band (called band because it goes around the circumference) i once felt tipped on the edge and it was still there at the end of the season.

no combustion takes place in the squish band area at TDC.

squish clearance is therefore closer-as desired. if you read lineweaver's comments more closely you'll note that he says that if the piston is flush with the top-there will be the desired .050" squish gap and not for instance .080"-.100" which renders the squish ineffective and therefore non-existent.

he's basically saying that it'll come good, stop worrying, you can get on with it.

Taffy

First let me thank all who responded with this chain tensioner dilema. One thing that still puzzles me though is this. The bike had and still has no base gasket so even if this 2000 bike has a pre 1997 cylinder then the chain should be too loose not too tight due to the shorter cylinder or so I would think. Dale thanks for the comments of "SQUISH" as it makes clearer to me and others what this is. Looks like .040 might be comming off the base and like you say I'll need to check the valve clearance. I suppose the piston's valve indents would need some machining if this clearance is not adequate. Do you happen to know what the clearance should be for a 2000 FC 501? Still very puzzled though why this is happenning. Sounds a bit unique. Speeking of unique I would like to say that the loyalty to the bike is something unheard of. With all the dealership, part issues and the like, you guys defend this ride like no tommorrow. Hope someday soon I will get to ride this steed and experience what you all have. Hats off to the operaters of this site as well. Thankyou and I will gladly donate to the cause.

yes it's a good idea to check piston to valve. if you can just get it together enough now to check: what you need to do is put a blob of plasticine in each valve pocket on the piston, smear it with oil so the plasticine stays with the piston and not both.

put head on and set with just a coupla head bolts in etc. turn engine over once, strip and measure plasticine depth where the valve had touched it. you'll have around 4-5mm and you need a minimum of around 2mm.

to measure it i use the 'foot' of a vernier.

i don't think you'll have any trouble.....


Taffy

Hi John,
Early Husaberg engines could aquire quite a large tolerance stack.
What you are experiencing is not unheard of.

My suggestion:
With the head and head gasket removed bring the piston to TDC. Measure the piston protrusion / recession. If positive subtract from .050". if negative add to .050". The sum will be your rough deck clearnace (aka squish clearance). Adjust as required to obtain a minimum deck clearance of .040". Remove just enough cylinder base material to accomplish your objective. Mock up assembly and check clearances as per instructions supplied by Taffy.

Notes:
To avoid cylinder plating damage remove material only from the cylinders base. Be advised that when you alter deck height in this fashion cam timing will be affected and should also be confirmed. I have safely run a minimum valve to piston clearance of .060".


Hope this helps.
Best Regards,
Dale

Well just a follow up on my cam chain tension issue. It seems that the boys at Nevada Cycle suggested modifying the earlier tensioner (steel) to achieve the proper tension. I guess you can cut off part off the tensioner. Has any body heard of this? Curious as ever.

Hi Buckwheat,
As per our phone conversation:
It sounds to me as if they are attempting to install a post 2000 tensioner in a pre 2001 engine. If this is the case simply have them cut the crimping from around the aluminum button and remove said button. They will then have a pre 2001 tensioner in hand.

Hope this helps.

Kind Regards,
Dale