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Engine Swap (b27 to b25) cluster question!

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    Engine Swap (b27 to b25) cluster question!

    Hello, I recently had an engine swap done on my 1987 325e. Swapped out the m20b27 engine with an m20b25 from a 91' 325i. I still have the original 325e cluster in the car.

    So everything in the cluster works except for the tach. My understanding is that for everything to work I have to swap in a later model 325i/is cluster? Is it a simple "plug and play?"

    My other option is to send out the cluster to be refurbished and have the tach properly set to the higher RPM. I am thinking of sending it to e30_dad.

    Just wondering what my options are, I am trying to keep this on a budget, haha.


    All E30 clusters are compatible electrically, all you would need to do is swap in a 7k tach and a 325i coding plug, the whole cluster does not need to be swapped. You will need to swap parts from a same generation cluster though.

    If your tach does not work, it could be the tach signal wiring to your cluster. Also a dead SI board inside the cluster is a very common part to fail and this will cause no tach operation.

    If you are going to have your cluster refurbished, send it to us. I do not consider E30_dad to refurbish clusters but more of "repair" them using known good used parts. This is because he does what it takes to get the cluster working again but the cluster can still fail prematurely. I know this because we used to refurbish parts for him about 7 years ago until he would take our quality control stickers off and use his own, telling people he was the one that did all the work. Now we are not affiliated in any way. Bavarian Restoration takes a far different approach and we actually refurbish them.

    This main difference between him and us is the refurbishing of the SI board, at least. He replaces the batteries and capacitors only, which is a huge mistake. There are about 20+ transistors and voltage regulators on the SI board which are also 30+ years old and some of them fail. When you swap in new SI board batteries without changing these transistors, it can lead to permanent failure of the SI board and we sell refurbished ones for $800 so its best to have it refurbished right the first time around to avoid a costly replacement. We replace all batteries, capacitors, transistors and voltage regulators for a truly refurbished product. This is why replacing the batteries only is a terrible idea.

    When we first started this business we would change only the batteries and capacitors like him. After receiving many returns that same year, we starting changing all the transistors and voltage regulators. 9 years later and we have not had any SI board returns after refurbishing multiple hundreds of them.

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      Thank you so much Gregs very informative. Also, the work you guys do at BavRest... Wow! Will definitely consider you if the cluster stuff is too much for me or when i inevitably need a full refurbish.


        This issue isn't your cluster, the real issue is your wiring. You need to jump two wires in the glove box area to get your tach working again. It's been almost 7 years since I did mine, but I had the same issue after swapping a M20B25 in my 87' 325e. Search around on here you'll find the thread.

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        1992 325i-S50 Swap

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        1991 325i Convertible Laguna Green (SOLD)
        1987 325i (SOLD);1992 M tech 2 Convertible (SOLD)
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        1992 325i Convertible Schwarz (SOLD)
        1992 318i Convertible Project-Finished (SOLD)