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Chamer66
  • Rank:XL Board Member
  • Posts:7
  • From:United Kingdom

Date Posted:05/24/2018 6:07 AMCopy HTML

Firstly hi as this is my first post.
Looking to build an XL 250 motor for MX. What's the biggest bore (don't mind boring out the cases) that's realistic with the standard rod, and what sort of compression, valves etc.While keeping the motor reasonably reliable?
Thanks in advance

1oldgoat #1
  • Rank:Gold Member
  • Posts:140
  • From:USA

Re:XL250 for MX Biggest bore

Date Posted:05/29/2018 4:30 AMCopy HTML

 Well there is a few things you can do.

First you can install the larger 350 valves in the head which with some port clean up works real well. The 350 camshafts can be run as well as springs. Have the original rockers hard welded and your good to go!

In days long past various bore/stroke combinations could be had to bring you up to 340cc, with a 290cc option being popular. Sadly you have to get creative with parts sourcing with the smaller Honda these days. Large bore piston kits do pop up now and then on ebay. Piston pin diameter prevents any 350 pistons to be used. 


David

Chamer66 #2
  • Rank:XL Board Member
  • Posts:7
  • From:United Kingdom

Re:XL250 for MX Biggest bore

Date Posted:05/29/2018 5:26 AMCopy HTML

 Cheers once again. Been chatting with Davey and he uses an XT350 piston. So may look in to that one?
John



Go soothingly on the grease mud ... as there lies the skid demon! ...






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