diving into a 345 rebuild.

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diggum

Member
Well upon removing the motor from my Scout it has become apparent that the rear main seal is toast and I May need new rings due to the exessive smoke comin from the Scout.

I have rebuild an engine before but not one of these... But before I embark upon this journey... Im curious if there is a typical machine shop regimine for these motors. Im assuming 3 angle valve job heavier valve springs , port n pollish heads... And anything that needs repaired. Is there anything else... Please guide me oh wise ones.
 
Check the cam bearing and make sure the cam is not flat. Bad cam bearings and a flat cam results in low oil pressure and the timing gear to be chewed up, and the engine dying. In previous cases, an engine that I got going sounded fine, but when taken apart, the whole cam was flat and timing gear was destroyed. And the rocker assembly was destroyed due to the oiler ports on the rocker being clogged.
 
diggum said:
well upon removing the motor from my Scout it has become apparent that the rear main seal is toast and I May need new rings due to the exessive smoke comin from the Scout.

I have rebuild an engine before but not one of these... But before I embark upon this journey... Im curious if there is a typical machine shop regimine for these motors. Im assuming 3 angle valve job heavier valve springs , port n pollish heads... And anything that needs repaired. Is there anything else... Please guide me oh wise ones.
Click to expand...

You need to decide what you want as far as performance out of it. The typical hot rod upgrades won't do much really. To satisfy your urge to poor money into your 345, you can do a mild port smoothing with most effort put into the valve bowls, guide bosses and removing the exhaust port bump. That's about it. It will never be a screamer. Put the most mild cam you can buy in it and make sure it is installed per the cam card. That requires you getting familiar with degreeing a cam, if you are not already.

I assume it is a 345e with the flat top pistons. Pay close attention to maintaining the compression ratio. If you go with a composite (not the thin steel) head gasket. Make sure to remove the thickness difference from the block deck. Only use stock compression height 1.891 (center of the piston pin to top of the piston crown) pistons like silvo-lite. Most of the others are destroked and have a shorter compression height.

Of course completely disassemble the rocker assemblies including the end plugs. Inspect for wear and replace as needed. The assemblies are available rebuild in the IHPA store.

Valve/head rework should use the normal 30/45/60* angles to set margin widths and locations. No more is needed.

From a machine work and new parts perspective, it needs to come apart and be measured. You May be able to get away with a re-ring and refreshing of the other parts. However if your rings are really wasted, you will need to bore it.

Post up here with what you find and we will point you in the correct direction.
 
Ok thanks ! Gonna tear it down n take it to the machine shop first . Make sure I don't need diff sized bearings before I order my rebuild kit . Was thinking of boring .20 over but after your suggestions I'll determine engine wear n tear first ! Thanks again
 
As far as what I'm looking for out of the engine , not much reliable better gas mileage, I really like camping and fishing , maybe a lil more romp n stomp ... But nothing crazy .
 
Ok , machine shop results have come back , one cylinder is pretty scored up , needed anew valve seat ... But that's it as far as what's needed . Exhaust ports will be ground , block n heads resurfaced , line bored ,3 angle valve job ... Other than that I haven't seen or heard of anything else being done . But I'm not trying to build a big hp motor either .
 
Line bore is tricky on a gear-drive cam motor like these. You'll be moving the crank closer to the cam. This isn't a problem with a chain or belt driven cam, but it will change the clearance in gear driven arrangement. Hard to believe this engine actually needs that procedure.
Also, if one cylinder is scored up pretty bad, it would need to be bored (along with the others to be even). Did you mean the exhaust valve in one cylinder is hashed? If the bores are within spec, a light hone and new rings would be a great cost-saver. Hopefully that's the case.
Show some pics!
 
Sorry about no pics ... I can show pics of the tear down but machine shop was still working on it when I went ... I don't have any pics of the good stuff . Yes cylinders will be bored .20 over to compensate for damage , exhaust ports will have the jump removed for better flow , if the line bore hasn't been done I'll ask machinist to hold back for clearance issues . He said they had rebuilt one for 2500 not long ago , I assume he has an idea of what he's doing but I could just be too trusting
 
You mention line boring. Don't. I've not ever seen an sv of any of its four popper twins that needed it.
Also by design the process of line boring moves the main bearing center line up in the block. This makes the cam and crank closer together. The timing set will have to be remachined to work. Really not possible. I've dealt with fixing that. Not fun.
 
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