250 thrust washers are they needed ??

In regards to another thread I had the same question. The newer Wisco piston have much less distance between the two journels of the wrist pin mounting hole s So do we need these spacers

Well yes. I thought maybe we could run the longer wrist pin bearing like you can do on the 390 an leave the thrust washer out. No leave them in. The spacers in the 390 are not really thrust washers they just keep smaller width std beariing on track. In 250 these are true thrust washers.

But looking at 250 I beileve the size of ports compared to even open bike needs the thrust washers for stability as in keeps everything tidy , straight and aligned in that 250 barrel even with piston journals so much narrower than the old Mahle. Maybe just thinking out loud ( in writing ) anyway i in regards to another thread. These washer are hard to find

It depends on the clearance between the piston and the small end of the con rod. Husqvarna sets the con rod centering within the piston; ie piston centered con rod as opposed to crank centered like most other engines. The con rod would float from side to side without properly shimming the clearance. This is not unique to the 250. The other engines have this in common. If the clearnce between the small end and inside wall of the piston are large, clearance divided by 2 and each spacer should be .001-.002 smaller to allow for thermal expansion.

As I have a modelmaker lathe in my workshop I would make them as needed.

I am starting a programming school so when I make enough money I will be looking for a CNC Mill and CNC Turning center for proving out programs. I am not above using Cafe Husky projects as student required projects. I like to teach with useful and real life occurrences in manufacturing as those were projects I saw early in my toolmaking career.

On 500s with mahle pistons and 2mm narrower than original yet top quality smallend bearings i installed 1mm thrust washers on either side. These were reputable items supplied from 2t manufacturers in Holland.
Both engines had a washer disintegrate at around 30hrs, coughing the pieces through transfers and boost ports with total destruction the results.
Even the wrispins were grooved where the washers situated.
Subsequently ive run the extra 2mm tolerance without the washers and zero failure after 100hrs plus.
Pull inlet manifold and reeds, check by cranking at btdc for dwell and play every 20hrs. Should be none as when new.
Ps. There are some really bad smallends on the market as well and ive seen dwell and tolerance on new ones. There should be none.

Husqyhamm - wow very interesting feedback.

I have never used washers on my Husky engine restorations. Mostly Wiseco pistons kits. No problems at all experienced in many years racing.

hi all,
i am in the midst of a top end rebuild on a 1979 cr390 and realized the piston to small end rod clearance is 2 mm shorter so the original spacers do not fit. with out the spacers the play will be 2mm on either side. i have tried to find spacers that are 2mm thick, but like said previously they are extremely hard to find. could i fit a wrist pin bearing that is 2mm shorter and use the 3mm spacers that i already have.

from what i read above it seems that maybe the 2mm on either side is not an issue and can forego the spacers altogether.
look forward to your thoughts.

This thread is 2.5 yrs old call Vintco they will help you out. You can start your own thread on you 390, I'd like to see it. Chris
And what HuskyHamm said!

I had the same issue with both my 1978 390's (same top end as the 79).
I used a Kawasaki small end bearing that is slightly wider than the Husky one. It still leaves the required clearance. The bonus as far as I am concerned is the the small end rollers get more oil as they are not shielded by the washers and you can see the end of the rollers. I have done many miles on both of mine with zero issues. The 390 Auto runs very hot due to the nature of the auto box, not even a hint of trouble when I have checked it.

Thank you! Will order one of them!

The best bet is to use the widest small end bearing that will go in the piston gap. The old washers did a great job of not giving the small end bearing enough lubrication!!!

Andy.