2.0 top end rebuild, waste of time? Options

[machina]

I really want to make our next race weekend with the SCCA in about 1 month.

The 1.7 is on its 9th life. I am amazed how this little motor just keeps going and going after 30 years and god knows how many miles. I have run 7 races and 2 test days with the motor and it won't quit. Finish in the top 1/3 in my group too.

Anyway I have the 2.0 now and was thinking of doing the top end and putting on 40 IDF's.

I would have the heads done at HFM and use a set of 96's from brad or maybe mahles.

How do I know if the bottom end of the motor is OK? I have read that running carbs with the stock cam loses power and I have read you can gain a bit.

What Think?
dr

[ArtechnikA]

How do I know if the bottom end of the motor is OK? I have read that running carbs with the stock cam loses power and I have read you can gain a bit.

rod bearings have a hard life in our motors. "As Long As" the heads and cylinders are off, have a look at the rod bearings and mike the crankthrows. if they're decent, and there are no other indications of main bearing issues (excessive thrust, for instance) and the cam lobes look good, you might be more inclined to believe the mains are good too. if the rod bearings show signs of abuse, i'd think you'd have to be a little skeptical about the mains too.

while the rods are out is a good time to have them reconditioned and balanced if you're inclined to do such a thing.

since the OEM injection doesn't really show any indication of excessive leanness over its operating range, i wouldn't think there's that much to be gained by changing from injection to carbs with the stock cam. maybe if freshly ported heads can flow more air at the stock rev ranges, and if increased compression (power) results in a requirement for more fuel, there could be some gains, i suppose ...

[machina]

As Long As" the heads and cylinders are off, have a look at the rod bearings and mike the crankthrows. if they're decent, and there are no other indications of main bearing issues (excessive thrust, for instance) and the cam lobes look good, you might be more inclined to believe the mains are good too. if the rod bearings show signs of abuse, i'd think you'd have to be a little skeptical about the mains too.

I am totally green.

Can you outline how to mike the crankthrows and check for excessive thrust?

Thanks,
dr

[Jake Raby]

Split the case....

[thesey914]

before you remove the rods I read somewhere that if the rod slowly drops under it's own weight then this is a good indication that the bearing is ok.
Otherwise use a micrometer with enough clearance for 50mm and measure the crank where you removed the rod.
Or you may find it easier with some digital vernier calliper. Check the figures you measured against the factory tolerance values.

-J

[RocknRollFrenzy]

use a micrometer, its much more accurate. with calipers its far to easy to have them twist/slide a little without noticing it. digital calipers can be re-zeroed aslo, which can lead to inaccuracies. all you have to do is have a little grime on the blade when you turn them on, and your measurement is off.......little carry-over from a past life as a machinist. (IMG:style_emoticons/default/wink.gif)

[machina]

Split the case....

I want to split the case but have a tight deadline.

Also, I am kind of worried about what to do with the crank, all the main bearings, etc.

Your video is great but I am still not sure exactly what has to be done with the case, crank, etc. does it all get sent out to machine like the heads?

I figured I could run the top end rebuild for a couple races while I do a full rebuild on my other motor.

dr

[Mark Henry]

I would say the cam/lifters will have the most wear of anything.

Keep beating on the 1.7 and do the 2.0 right. (IMG:style_emoticons/default/smash.gif)