re-bore or not re-bore?

[xrvirgin]

this is going to be a quick question,,

my XR400 is loosing compression, the last time it did this it was the rings sticking in the groove's on the piston,
so I'm thinking should i have it re-bored or should i bite the bullet and go for the 440 kit?

ATV unlimited do a full kit (barrel, piston, rings, clips, pins, top end gasket set) for about £250ish.

would this be a better route to down as if i did go for the re-bore, i could probably spend nearly that on a piston, rings, gaskets, and so on?

[AIRWOLF]

Don't go to 440. . . . . short answer.

[xrvirgin]

i take it its not a good idea to go with the 440 kit?????

what would be a good re-bore size while still keeping stability on the cylinder wall?

[jasonbc]

i take it its not a good idea to go with the 440 kit?????

what would be a good re-bore size while still keeping stability on the cylinder wall?

yeah look at this a 440 kit with a few other bits













The only reason 440 kits get fitted are because it's cheaper than getting the job done properly. What you've just seen is the result of metal fatigue in the rod and over-revving with the 440 kit. Every bike i've known to have a big bore kit fitted has **** it's load drastically. Don't go down that road it aint worth the hastle. Testament to the motor though, if you look at the secind photo (i know its small) but the 2 faces have polished each other, which means it had run rather fu**ed for a while before the motor let go...........................

Don't rebore to a bigger size for about £70 you can get a new liner pressed into your exhisiting cyclinder

[416cc]

this is going to be a quick question,,

my XR400 is loosing compression, the last time it did this it was the rings sticking in the groove's on the piston,
so I'm thinking should i have it re-bored or should i bite the bullet and go for the 440 kit?

ATV unlimited do a full kit (barrel, piston, rings, clips, pins, top end gasket set) for about £250ish.

would this be a better route to down as if i did go for the re-bore, i could probably spend nearly that on a piston, rings, gaskets, and so on?

Low compression can be valves seats as well as piston & rings...I presume the valve clearances are ok...? Does the bike drink much oil? Is the spark plug fouled with oil burning? Can you do a leakdown check? This would tell you whether it was valves or piston rings. Are you running fully synth oil?

I have a 416 Wiseco kit in my XR...the piston is the same weight as the OEM slug so there's no added strain on the rod. The compression ratio was bumped up to 10.25:1 so I added an extra base gasket to reduce this slightly. It gives an extra bit of zap but I never over-rev the engine...it's not meant for continuous high revs as valves tend to drop, with disasterous consequences.

[xrvirgin]

damn, see what you mean with the stress of over reving the motor with the 440 kit on, must have been some serious metal failure from the rod top.