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Compression loss.....after a few tanks?

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Old 09-18-2005, 10:22 AM
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eye one
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Default Compression loss.....after a few tanks?

So trying to fine tune the Collari after 8 or 9 tanks I noticed it would cut out after it got up to temp, around 220-240. Thinking it could be the LSN too lean, or maybe the glow plug is too hot.

Low and behold I can rotate the flywheel with one finger. Yeah there is a resistance, but it can still turn over with just one finger.

It's never really gotton hot (260 max), and I have taken every precaution possible to keep it clean and maintained. Always set it to BDC while breaking it in, use after run oil when it would sit, never ran without a clean filter, and haven't even ran it in dirt. Oh, and it has been running rich.

Why would it lose compression so easily, I don't get it. Or is normal on this big block to be able to turn it so freely? I can't imagine how I could have scored the piston and sleeve but this would explain the thing cutting out and difficult to start when hot. The head is on tight, I even sealed the backplate and carb with RTV sealant (they say it's not neccessary but it's a habit)

Maybe the removal of a head shim would help? What else should I look at. Makes no sense, hoping someone will tell me I am over reacting & it's normal, and to keep tuning.
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Old 09-19-2005, 08:39 PM
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Default RE: Compression loss.....after a few tanks?

you could try changing out the glow plug and washer it could be you're not getting a good seal around there.
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Old 09-19-2005, 09:30 PM
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Default RE: Compression loss.....after a few tanks?

Does it still make good power? And does it start easily? If so then I wouldnt worry about it too much.
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Old 09-20-2005, 08:13 AM
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Default RE: Compression loss.....after a few tanks?

Yeah it starts easily (the one-way bearing slips though) and it runs real strong. I am still getting use to it, I am starting to think it's more of a tuning issue. I will try a cooler plug and richen the LSN more. Just surprised with the lack of compression, another Collari owner mentioned they can turn theirs over easily with one finger when cool too.
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Old 09-20-2005, 08:57 AM
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Default RE: Compression loss.....after a few tanks?

ORIGINAL: eye one

Yeah it starts easily (the one-way bearing slips though) and it runs real strong. I am still getting use to it, I am starting to think it's more of a tuning issue. I will try a cooler plug and richen the LSN more. Just surprised with the lack of compression, another Collari owner mentioned they can turn theirs over easily with one finger when cool too.
Keep an eye on the one-way bearing. Dont let it slip too much. The residual fuel left left in the engine or after-run oil is leaking on the the one-way shaft (normal). Its a good idea to spray it out (the one-way shaft) with motor spray once in awhile. The compression loss is normal. Ever run an 8th scale on-road engine from JP? Pinch is no good and we dont consider and engine fully broken in until there is no pinch at all. Dont be fooled by the hype that tight compression is good. As long as your not suffering blow-bye you'll be ok.

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Old 09-20-2005, 02:55 PM
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Default RE: Compression loss.....after a few tanks?

Right on, thanks for the reply. Others have mentioned the same concerning the compression and the Collari. I guess other big blocks are similar huh? Always thought a loss of compression equates to the symptoms I am having and indicate time for a re-build.

Good to know, thanks. Now to just get some cooler plugs.
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Old 09-20-2005, 04:32 PM
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Default RE: Compression loss.....after a few tanks?

Try some quality fuel too. The new Werks fuel is awesome. Cooler temps and more run time. Look for a write up on it soon in one of the magazines. Dyno numbers speak the truth. Just be prepared to make some engine adjustments when switching over to the new fuel. I went 4-5 hours leaner on the top end. You dont want to switch up you and your buddies fuel bottles if your running different brands. The engine will go way.....lean and may casue damage.

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