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Post by scooter7878 on Aug 28, 2021 19:35:38 GMT -5
105 compression is not enough the engine will not make good power with that compression
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vacationer
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Post by vacationer on Aug 28, 2021 22:36:02 GMT -5
Should I drain the old oil (to check for fuel) before or after I retest for compression?
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Post by scooter7878 on Aug 29, 2021 1:30:41 GMT -5
Do the wet test first if it it washed down with fuel the compression will come up. Discount the fuel hose to carburetor and vaccume hose from fuel petcock before doing compression test to stop any extra fuel from going in cylinder. If compression doesn't come up any u have valve train issues and no point changing oil. If it comes up more than 5 psi y can try changing oil and recheck if not better u got worn rings or cylinder
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Post by GrumpyUnk on Aug 29, 2021 8:28:35 GMT -5
Have the valve clearances been checked? They don't need a lot, but they do need a little to keep the valve free to make good contact with the seat. The clearance may prevent the valve seating, and thus prevent it from sealing, which would tend to lower the compression.(and possibly let the valves get too hot and fail). The valves transfer heat(exhaust mostly) to the valve seat whenever they are closed. Yup. Fractions of a second, but it apparently adds up and if the valves do not touch well enough to make good contact, they will likely fail.(burn) tom
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Post by scooter7878 on Aug 29, 2021 8:45:33 GMT -5
Have the valve clearances been checked? They don't need a lot, but they do need a little to keep the valve free to make good contact with the seat. The clearance may prevent the valve seating, and thus prevent it from sealing, which would tend to lower the compression.(and possibly let the valves get too hot and fail). The valves transfer heat(exhaust mostly) to the valve seat whenever they are closed. Yup. Fractions of a second, but it apparently adds up and if the valves do not touch well enough to make good contact, they will likely fail.(burn) tom . I believe I had him check it but there's been a lot back and forth so I don't remember but pretty sure I asked him about that
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vacationer
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Post by vacationer on Aug 31, 2021 12:21:21 GMT -5
Okay I put some oil down and only got one try in before the battery died. Got up to 125 though! Feeler gauges should be arriving today, so I'll take the head off when the rain stops and measure the valves as well as check for carbon buildup. Then I'll change the oil for good measure and takes her out for a test. If I'm still SOL, I guess I'll order a new piston head and maybe take a look at the timing belt.
Am I missing anything?
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Post by scooter7878 on Aug 31, 2021 13:45:57 GMT -5
If it came up from 105 to 125 ur problem lies in the piston rings or cylinder wall. U can try changing oil than put some oil down spark plug hole like u did. Crank it over a few times with plug out than install plug and drive see if it gets better if ur oil was fuel fouled or cylinder was washed down it will be better if not u need a cylinder if it came up to 125 the valves are not ur issue. It was either washed down with fuel causing low compression or u got worn cylinder/ rings. Try the oil down cylinder and oil change and drive if it's not better with that get a cylinder and I would get a head also just to start fresh. If u want to try reuse head when u have it apart lmk and I'll tell u how to check head for cracks and valve seal but there cheap enough I'd just get a kit
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vacationer
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Post by vacationer on Aug 31, 2021 18:25:07 GMT -5
So I opened up my oil tank and found that there was no oil. This made sense because I'd forgotten that all the oil leaked out last week and I'd neglected to refill it. So I refilled it, put some more through the spark plug hole and retested compression. Couldn't even get to 100.
The feeler gauges came so I decided to go ahead and measure valves. Bottom was good, top was .0011 so I fixed it and put the cover back on. Tested for compression again, no change. Took her out and couldn't get more than ~13mph.
Looks like amazon has the piston head for cheap, so I'll get that.
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vacationer
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Post by vacationer on Aug 31, 2021 18:29:22 GMT -5
Strike that, I'd rather keep the head.
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Post by scooter7878 on Aug 31, 2021 19:29:35 GMT -5
When u get head off get a can of carb cleaner from auto parts store. Hold head so the valves are facing down and fill the intake port with carb cleaner. When u spray it in tilt head slightly to help fill the port with cleaner and only lightly press button on carb spray u don't want a powerful stream u just want it to come out slowly and fill port without blasting all over. Be sure before u fill port that the valves are dry in the underneath as u are looking for any wetness seeping from the valve so dry it good u can spray bottom of head with cleaner first but shake it and let it all dry before testing. U should see no wet stain drip or anything coming from valve with the port filled repeat on exhaust side. Also wire brush the head lightly in-between the two valves and clean and look for any cracks in between the valves on the head.
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Post by scooter7878 on Aug 31, 2021 19:33:57 GMT -5
Scooters to go on e bay has 50mm airsal high compression Pistons and a cylinder for 60 bucks that's what I use his stuff is nice the cylinder is machined well and the domed piston makes more power bc of slightly more compression. The piston is also lighter than other 50mm piston by a good bit which is much easier on the stock crank less weight going up and down at high rpm is a big plus. He also ships same day and us very helpful. Any questions u have he responds right away. It's a quality Kik and it makes good power in a 50mm that's the kit I always buy u will be happy
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Post by scooter7878 on Aug 31, 2021 20:26:14 GMT -5
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Post by scooter7878 on Aug 31, 2021 20:27:14 GMT -5
This is another good kit it's a tiwan kit 52mm hc piston but it's harder on ur crank
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vacationer
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Post by vacationer on Aug 31, 2021 21:29:20 GMT -5
Lol I bought a piston and rings on Amazon for $10. Honestly, that's all I can afford right now. But that should be enough to know if a new piston really is the solution, right?
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Post by scooter7878 on Aug 31, 2021 21:59:24 GMT -5
That night work for a little while the problem with that is at the very least the cylinder needs to be honest and de glazed for the rings to seat properly the cross hatch pattern from honing the cylinder acts as kinda a file on the rings to help file down the rings to seat properly and that's assuming the cylinder walls aren't warped or out of round if the cylinder walls are warped or if the cylinder is out of round if it does work it won't work for long and probably won't have the best compression and possibly burn oil but even if cylinder is good without honing the cylinder u won't get proper ring seat and will at the best burn some oil and possibly be slightly low compression ur running a fine line with that it might work ok for a bit or might not. Y have spent a lotta time and money going at this it kinda doesn't make sense to play around to possibly save 40 bucks u believe even if it works it's not gonna work good and it's not gonna last too long but that's up to u. At the very least u can probably find a cylinder and piston in Amazon for 30 bucks u would be better off with that than just a piston
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