Ƙungiyar sandar haɗawa ta ƙunshi jikin sandar haɗawa, babban murfin kai na sandar haɗawa, ƙaramin sandar haɗi, ƙaramin sandar ƙauye, babban sandar haɗawa da babban sandar ɗaukar sandar haɗawa da kuma ƙullin sandar haɗawa (ko sukurori), da sauransu. Ƙungiyar sandar haɗawa tana fuskantar ƙarfin iskar gas daga fil ɗin piston, juyawar kanta da ƙarfin inertia na ƙungiyar piston. Girma da alkiblar waɗannan ƙarfin ana canza su lokaci-lokaci. Saboda haka, sandar haɗawa tana fuskantar matsi, tashin hankali da sauran nau'ikan nauyi. Haɗin dole ne ya sami isasshen ƙarfin gajiya da tauri. Ƙarfin gajiya bai isa ba, sau da yawa yana haifar da karyewar jikin sandar haɗawa ko ƙullin sandar haɗawa, sannan ya haifar da babban haɗari ga injin gaba ɗaya. Idan tauri bai isa ba, zai haifar da nakasar lanƙwasa na jikin sandar da kuma nakasar decircular na babban kan sandar haɗawa, wanda ke haifar da niƙa na piston, silinda, bearing da crank fil.
Jikin sandar da ke haɗa ta ƙunshi sassa uku, kuma ɓangaren da ke haɗa ta da fil ɗin piston ana kiransa da sandar da ke haɗa ta ƙaramin kai; ɓangaren da ke haɗa ta da crankshaft ana kiransa da kan sandar da ke haɗa ta, sannan ɓangaren sandar da ke haɗa ƙaramin kai da babban kai ana kiransa sandar da ke haɗa ta.
Domin rage lalacewa tsakanin sandar haɗin da fil ɗin piston, ana danna siririn bututun tagulla mai bangon waya a cikin ƙaramin ramin kai. Ana haƙa ko niƙa ramuka a cikin ƙananan kawunan da bushings don ba da damar feshewar ta shiga saman mating fil ɗin bush-piston.
Jikin sandar da ke haɗawa dogo ne, ƙarfin da ke cikin aikin ma babba ne, domin hana lanƙwasawa, jikin sandar dole ne ya sami isasshen tauri. Saboda wannan dalili, jikin sandar da ke haɗa injin abin hawa galibi yana ɗaukar sashe mai siffar 1. Sashe mai siffar 1 zai iya rage nauyin a ƙarƙashin yanayin tauri da ƙarfi. Ana amfani da sashe mai siffar H don injin mai ƙarfi. Wasu injinan suna amfani da sandar da ke haɗa mai ƙaramin kai don allurar mai don sanyaya piston. Dole ne a haƙa ramuka a cikin jikin sandar tsawon lokaci. Domin guje wa yawan damuwa, jikin sandar da ke haɗawa da ƙaramin kai da babban kai suna haɗuwa ta hanyar sauyawa mai santsi na babban baka.
Domin rage girgizar injin, dole ne a iyakance bambancin yawan kowace sandar haɗin silinda a cikin mafi ƙarancin iyaka. Lokacin haɗa injin a masana'anta, galibi ana ɗaukar gram a matsayin na'urar aunawa bisa ga nauyin ƙasan sandar haɗin, kuma ana zaɓar rukuni ɗaya na sandar haɗin don injin ɗaya.
A kan injin nau'in V, silinda masu dacewa a ginshiƙan hagu da dama suna raba fil ɗin crank, kuma sandar haɗin tana da nau'i uku: sandar haɗin layi ɗaya, sandar haɗin fork da sandar haɗin kai ta farko da ta biyu da kuma sandar haɗin gwiwa ta biyu.
