Author Topic: '48 LS Engine rebuild  (Read 2304 times)

Online Greybeard

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Re: '48 LS Engine rebuild
« Reply #60 on: 21.06. 2022 13:31 »
Sparks in the open air are a guide, HT does strange things under compression.
I remember using a testing and cleaning machine for plugs. There was a sand blaster section and a test section. The plug could be seen through a little window. When the plug was energised you could see a nice blue spark. Compressed air was blown onto the plug and the pressure was increased. If the plug was no good, the increasing air pressure would stop the plug from sparking.  I found this picture.
Greybeard (Neil)
1955 Golden Flash, sprung frame
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A Distinguished Gentleman Riding his 1955 Plunger Golden Flash

Offline fffcycles

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Re: '48 LS Engine rebuild
« Reply #61 on: 21.06. 2022 14:53 »
Thanks guys, I have new pick-ups, leads, caps and plugs installed and it ran quite well for two sessions of 10-15 minutes while setting the carb. Tried going down the road but it just would not go and carb leaked gas continuously so changed the float chamber, lowered the fuel level with an extra washer so things are good but now it does not fire on the left cylinder.
I have used the plug testers a lot, army workshops did not have them but every garage I worked at after that had them.
I should have another set of plugs delivered today, I will swap leads over and I am going to check compression properly again (finger in the hole is not a proper tool) as I have had head gaskets blow at start before.
There is something I have missed here and I will find it. I am hoping this one puts a smile on my face as I have another ‘48 waiting for rebuild and I want to feel it will be worth it.
Meantime it is worth airing these problems among like-minded riders.
Frank
Frank P
1948 A7 Long Stroke, a collection of BSA D1/B44/B50/A65 from the 50's thru 70's, Ariels/Nortons/Triumphs and a smattering of Japanese

Offline fffcycles

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Re: '48 LS Engine rebuild
« Reply #62 on: 22.06. 2022 13:28 »
Hell, I said a finger down the hole was not a good tool. 75/ 116 lbs compression left/right so off with the head and see what has gone wrong. I suspect a sticking valve, broken rings? I will see what is up in a day or two, have to take my wife for surgery this morning (not too serious) and that is more important for now.
Frank P
1948 A7 Long Stroke, a collection of BSA D1/B44/B50/A65 from the 50's thru 70's, Ariels/Nortons/Triumphs and a smattering of Japanese

Offline Swarfcut

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Re: '48 LS Engine rebuild
« Reply #63 on: 22.06. 2022 20:16 »
 Easy stuff  first. Tappet clearance...if it's not what you expect it's the valve/guide or a mis -placed pushrod. Or simply a poor locknut. Rocker boxes off to check freedom of movement of the rockers on the shafts.  Leakage test on valves- as a quick test put an airline on the plug hole and listen, cylinder set to TDC, valves closed. Custom adaptor useful here*. Ring problem unlikely, but worst case jug has to come off.

 Swarfy

 * Made one years ago from old plug, steel tube, airline connector. Used to hold valves closed to change valve stem oilseals on OHC vehicles without major dismantling. Beats the old rope trick.

Offline fffcycles

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Re: '48 LS Engine rebuild
« Reply #64 on: 22.06. 2022 22:51 »
Yes, take it in stages and I have an air line adapter for my compression tester with quick disconnect. Done a few jobs like that myself. Just a process of elimination and tracking down the fault.
Just to add insult to injury the back tire went flat on the last ride up and down the block, just have to laugh!
Frank P
1948 A7 Long Stroke, a collection of BSA D1/B44/B50/A65 from the 50's thru 70's, Ariels/Nortons/Triumphs and a smattering of Japanese