Can anyone shed a bit of light on the lapping subject.



I have recently rebuilt an engine and had to replace two plates as they where right on the edge of tolarance.



I have read that the housings can be lapped to reduce the depth of wear on them, but i have also read that the housings are coated (hardened) so is there a max amount that can be taken off?



Also is it possable to sort of DIY lap your plates or is it a job for an Engineering shop?



Thanks



Chris

 

i wouldnt diy the lappign, yes it does have a coating. if you lap them you should ptu some sort of a coat on teh surface, peopel do run them without the coat thought i amnot sure how much teh seals last that way.



only lap it if you absolutely have to do it, even some wear on the housing is not goign to be bad, i rather use one that is slightly worn out then lap it.



also if its nto alpped right the bearign surface and the lapped surface are nto gonan be perfectly parallel and that will cause some faster bearing wear

 

The plates are nitrided, this treatment is only so deep into the metal (forget how deep exactly) so you can only take off a minute amount of material before the plate is either useless or really needs treating again. What with the expense and hassle of lapping and the fact that you still are likely to have an 'inferior' plate a lot of builders replace rather than lap. And no, its a specialised grinding process not a DIY job.

 

https://www.nopistons.com/forums/ind...howtopic=36853



the pre 79 motors were not nitraded, just like a post 79 lapped motor would be. the nitrading does add durability; something like 2x the miles, but if your housings are shot then it cant really hurt.



on the 86-02 engines the key thing is the water seal groove depth

 

Racing beat heat treats them after lapping. They say its good if not better than stock.



GregW

 

We lap every engine we build unless the plates are almost perfect. If the plates are wore to the minimum then the nitride surface is already worn off in the low areas. We currently don't have a source to have the plates nitrided again but are working on it. We have mildly ported N/A engines with 70,000 miles on them. No problems at all. I feel you end up with a better overall engine if you lap the plates but the again its my opinion.