Compression problem on a evo 1340

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Jan 27, 2019 | 10:37 AM

rawmalta

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From: clevedon

Compression problem on a evo 1340

Have a weird problem on a 93 evo 1340, bought it for a project and started it up for the first time today, running like crap. Checked ignition and fuel all OK, checked compression front 100psi and rear 0 psi. Took the rocker cover off to see the movement and seemed ok, checked the compression again 100psi on the rear now, put the cover back 0psi. So with the cover on I get 0psi and when I remove it I get 100psi, what's going on.

Jan 27, 2019 | 10:42 AM

Kingglide549

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From: Viet Vet, crossroads

I would guess you have a rocker hanging up on the inside of the cover.
Is it a stock cam in there?

Jan 27, 2019 | 10:49 AM

rawmalta

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From: clevedon

It's a stock cam and I was looking at the top cover to see if there was any markings but I can't see anything.

Jan 27, 2019 | 10:56 AM

Kingglide549

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From: Viet Vet, crossroads

Take the rocker box back off look it over. Set it back on only with a couple fastener loose so it stays in pace but really loose .
Spin engine over plugs out with rear wheel- in high gear, see what you hear and see.
(obviously, you will have to have the back end jacked up a couple inches.)

Jan 27, 2019 | 02:19 PM

bustert

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or you could start it and then loosen the cover screw a tad each till you hear a noise. you then could use a mechanic stethoscope to localize the area. if the cover is clamping movement, you probably will not get much marking turning at crank speed or less. another trick is to machinist dye the cover and any contact area will show up.
grins and giggles, swap cover.

Jan 27, 2019 | 02:35 PM

TwiZted Biker

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From: Niles Canyon Ca.

Had a few after market rocker box's that needed clearencing on evo's or the exhaust spring retainers wound hit. What this sounds like , you have a valve hanging open.