kiwisuzuki1100nz Posted March 27, 2021 Share Posted March 27, 2021 Quick question. Is it ok to lap in slabbie valves with a light lapping paste? Read a bit that says no, dont do it and other posts where people do. Quote Link to comment
TonyGee Posted March 27, 2021 Share Posted March 27, 2021 i think the all depends on how bad they are. ? Quote Link to comment
HWB Posted March 27, 2021 Share Posted March 27, 2021 1 hour ago, kiwisuzuki1100nz said: Quick question. Is it ok to lap in slabbie valves with a light lapping paste? Read a bit that says no, dont do it and other posts where people do. No, you need to marry the valve to the seat properly, so coarse grit paste until you have a uniform seat all around, then fine paste to finish off Quote Link to comment
kiwisuzuki1100nz Posted March 28, 2021 Author Share Posted March 28, 2021 Sorry a bit more context. I read the valves and or seats have a thin hardened layer and that lapping them in can wear through the layer so shouldnt be done. Sounds like most do lap the valves in. Quote Link to comment
dupersunc Posted March 28, 2021 Share Posted March 28, 2021 8 hours ago, kiwisuzuki1100nz said: Sorry a bit more context. I read the valves and or seats have a thin hardened layer and that lapping them in can wear through the layer so shouldnt be done. Sounds like most do lap the valves in. Modern engines have coating on the valves so its a no no. If you've just had you seats re-cut, it's a no no as the seats will be crisper than you'll get with grinding paste. If you have an old oil boiler with signs of pitting or uneven seating then yes lapping them in will help, and is worth while. 1 Quote Link to comment
MeanBean49 Posted March 28, 2021 Share Posted March 28, 2021 (edited) Head upside down with plugs in, pour some petrol in the combustion chambers and watch for a bit, if they empty then they are not sealing and could do with lapping in. Whether you need to start with coarse and then have to do again with fine will depend on how bad they are. I generally find 99% of the time fine on its own will do the job Edited March 28, 2021 by MeanBean49 2 Quote Link to comment
Buzuki Posted March 28, 2021 Share Posted March 28, 2021 14 hours ago, kiwisuzuki1100nz said: Sorry a bit more context. I read the valves and or seats have a thin hardened layer and that lapping them in can wear through the layer so shouldnt be done. Sounds like most do lap the valves in. On oil cooled engines only exaust valves are with hardened surface , and that surface is not so thin at all , so you can lap all valves with no problems , personally I found that by exaust valves ordinary grinding paste was to soft so finally I have to use very hard diamond based paste to complete the valve job . 1 Quote Link to comment
Gixer1460 Posted March 28, 2021 Share Posted March 28, 2021 Just for balance, I haven't lapped ANY valves since I owned a Mini Cooper in the 90's! New valves with fresh cut seats or re-used valves back in their original holes, fit, gap, forget - job done. 2 Quote Link to comment
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